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Fire Service Manual, Volume 1, Fire Service

1. Electrical fires are not included in this system of classification see this Chapter Section 6 2 In the following Sections the general principles of extinguishment particularly in relation to fire fighting foams are reviewed for each of the above classes of fire 6 1 1 Class A fires Class A fires are those which involve solid materi als usually of an organic nature such as wood cloth paper rubber and many plastics Some manufacturers of AFFF AFFF AR FFFP FFFP AR and SYNDET foams state that their products may be used as wetting agents at between 0 1 and 3 concentration to assist in the extinc tion of class A fires For these fires AFFF AFFF AR FFFP and FFFP AR may be used at low and medium expansion while SYNDET foams may be used at low medium or high expansion There are said to be advantages in the use of wet ting agents when fires become deep seated In these conditions water can be slow to penetrate A wetting agent that reduces the surface tension of the water is claimed to greatly improve penetration to the seat of these types of fire When a wetting agent is employed a deep seated fire is predomi nantly extinguished by the cooling effect of the water mix rather than by the smothering effect of any foam that may be produced Surfactant based foams display some wetting agent properties but are more expensive than products sold purely for their wetting agent char acteristics From time to time a fe
2. Issued under the authority of the Home Office Fire and Emergency Planning Directorate Fire Service Manual Volume 1 Fire Service Technology Equipment and Media Firefighting Foam Technical HM Fire Service Inspectorate Publications Section Issued under the authority of the Home Office Fire and Emergency Planning Directorate Fire Service Manual Volume 1 ji Fire Service Technology RETURN OR RENEW ON OR BEFORE THE LAST V DATE STAMPED BELOW 2 RENEWALS MAX Equipment and Media FINES ARE PAYABLE ON ANY ITEMS FIRE SERVICE COLLEGE RETURNED LATE TO aes ee Firefighting Foam Technical THE FIRE SERVICE COLLEGE LIBRARY MORETON IN MARSH GLOUCESTERSHIRE GL56 0RH 01608 650831 Ext 2338 _library fireservicecollege ac uk The Fire Service College 7 Jor AVIV i 1 6 MAY 2000 FiRt SERVIGE COLLEGE MORETON IN MARSH GLOS GL56 ORK Pone oF os HM Fire Service Inspectorate Publications Section London The Stationery Office Crown Copyright 2000 Published with the permission of the Home Office on behalf of the Controller of Her Majesty s Stationery Office Applications for reproduction should be made in writing to The Copyright Unit Her Majesty s Stationery Office St Clements House 2 16 Colegate Norwich NR3 I1BQ ISBN O 11 341188 X Cover photograph The Fire Experimentation Unit Half title page photograph West Midlands Fire Brigade Printed in
3. The application of foam by projecting it over the sides of a storage tank and directly on to the surface of the contained fuel Measurement of the acidity to alkalinity of a liquid on a scale of 1 to 14 A pH of 7 is neutral like that of pure water a pH of ts very acidic a pH of 14 is very alkaline This term is generally used to describe any liquid which destroys standard foams although it actually refers to liquids whose mole cules possess a permanent dielectric discharge e g Alcohols ketones Most polar solvents are water miscible The lowest temperature at which a foam concentrate 1s fluid enough to pour This is generally a few degrees above its freezing point Preburn time Premix solution Primary aspirated foam Proportioner Protein P foam concentrate Relative density Secondary aspirated foam Security Shear strength Slop over Solution transit time Specific gravity a ae ee The time between ignition of a fire and the commencement of foam application A mixture in correct proportions of a foam concentrate and water Use of this term generally implies that the foam is stored in a premix form as in a portable foam fire extinguisher or as foam solution in a fire appliance water tank Finished foam produced from foam solutions that are passed through purpose designed foam making equipment See secondary aspirated foam A device where foam concentrate and water are mixed to
4. The mass per unit volume of a material mass Density volume See Bund area The discharge rate of a high expansion foam generator measured in cubic metres min m min of foam at a stated expansion ratio The time taken for a percentage of the liquid content of a finished foam sample of a stated depth to drain out of the foam For low expansion foam times taken for 25 of the foam solution to drain out are usually given for medium and high expansion foams 50 drainage times are usually given The ratio of the total volume of finished foam to the volume of foam solution used to produce It Expansion ratio volume of finished foam volume of foam solution used to produce it A finished foam foam solution or foam concentrate that forms a spreading thin aqueous film on the surface of some hydrocarbon liquids Film forming fluoroprotein These are fluoroprotein foam concentrates which have the ability to form an aqueous film on the surface of some hydrocarbon fuels Firefighting Foam Technical 83 Finished foam Flammable liquid Flashback Flashpoint Flow requirement low and medium expansion Fluoroprotein FP foam concentrate Foam Foam concentrate Foam dry Foam generator high expansion Foam generator low expansion Foam making branch foam making branchpipe FMB Foam monitor Foam solution Foam wet 84 Fire Service Manual The foam as applied to the
5. in higher viscosity 4 i 8 Fire Service Manual Firefighting Foam Technical 89 o S ee Published by The Stationery Office and available from The Stationery Office mail telephone and fax orders only PO Box 29 Norwich NR3 1GN Telephone orders General enquiries 0870 600 5522 Fax orders 0870 600 5533 www itsofficial net The Stationery Office Bookshops 123 Kingsway London WG2B 6PQ 020 7242 6393 Fax 020 7242 6412 68 69 Bull Street Birmingham B4 6AD 0121 236 9696 Fax 0121 236 9699 33 Wine Street Bristol B51 2BQ 0117 926 4306 Fax0117 9294515 9 21 Princess Street Manchester M60 8AS 0161 834 7201 Fax 0161 833 0634 16 Arthur Street Belfast BT1 4GD 028 9023 8451 Fax 028 9023 5401 The Stationery Office Oriel Bookshop 18 19 High Street Cardiff CF1 2BZ 029 2039 5548 Fax 029 2038 4347 71 Lothian Road Edinburgh EH3 9AZ 0870606 5566 Fax 0870606 5588 The Stationery Office s Accredited Agents see Yellow Pages and through good booksellers 15 ISBN 0 11 341 188 9 780113 411887
6. Burnback resistance is the ability of a foam blan ket to resist destruction from direct contact with heat and flames Such contact occurs during initial foam application where the foam blanket will be continually covering and moving against flame It can also occur once successful foam application has been achieved from a small area of sustained burning or from a new ignition source Burnback resistance 1s one of the main properties assessed when testing the firefighting performance of foams Usually once a test fire has been extin guished the burnback resistance of the foam 1 Expansion Test Foam Solution 2000cc Foam 2000cc Weight of a given Volume of Foam Solution Expansion Weight of same Volume of Foam 2 Drainage Time Test 25 of Liquid content of Foam Figure 4 1 Diagram showing tests to determine foam properties 1 Expansion test 2 Drainage time test Firefighting Foam Technical 5 blanket is assessed Either a small area of foam is removed and the fuel underneath ts re ignited or a flame is continuously played on to a small area of the foam blanket The measurement made is known as the burnback time This is the time taken from re igniting the fuel or applying flame to the foam blanket until the re involvement in flame of an area of the surface of the fuel Often it is the 25 burnback time that is quoted for the burnback resistance of foams This is the
7. Working slows down the foam stream within the branch due to the energy required to produce foam Consequently the more a foam is worked within a branch the less the distance it can be projected 4 3 Foam Flow Fluidity Finished foams that rapidly flow across the surface of fuels and around obstructions can lead to quick flame knockdown and control of a fire This can be particularly important in aircraft or vehicle crash fire situations where there is a significant risk to life Critical shear strength 1s a measure of the degree of stiffness of finished foam and gives an indica tion of its ability to flow Shear strength is mea sured by a paddle type torsion wire viscometer These are specialist items of equipment and are not suitable for routine fire service use Shear strength figures can only be reliably compared if the same type of measuring equipment and measurement methods are used However these measurements do not provide a reliable indication of the fire fighting capability of foams 28 Fire Service Manual Protein and fluoroprotein foams tend to be stiffer and hence they give higher shear strength mea surements than SYNDET AFFF AFFF AR FFFP and FFFP AR finished foams However the shear strength of finished foam also depends on the amount of working provided by the branch used to produce the foam see above Secondary aspirat ed equipment will produce foam of low shear strength while primary aspirated eq
8. imens Unfortunately the range and type of test speci mens that are tested varies widely as does their susceptibility to the effects of the substance For most foam concentrates only the foam manu facturers toxicity information is available very few independent tests have been carried out Toxicity testing can be very expensive to perform Consequently some foam manufacturers do not provide comprehensive values others provide val ues for a small or wide range of test specimens including algae water flea often Daphnia Magna and fish often either rainbow trout or fathead Firefighting Foam Technical a7 minnow However it is extremely difficult to compare the toxic effects of foam concentrates unless the same specimens test conditions and toxicity measurement criteria are used A review of firefighting foam concentrates carried out by the Water Research Council on behalf of the National Rivers Authority during 1994 Reference 6 concluded that all of the toxicity data they col lected from various sources particularly manufac turers indicated that none of the foam concentrates were of high acute toxicity to test specimens They found that most foam concentrates were tested on water flea or fish although indications were that testing on algae would have produced results for a more sensitive species From the data they collected some SYNDET foam concentrates appeared to be the most toxic and all of the pr
9. International and European standards have been produced for procure ment of all types of foam concentrates which meet minimum performance requirements for general firefighting appli cations DEF STAN 42 40 specifies requirements for foam concentrates for controlling and extinguishing hydrocarbon fires in aircraft ships and vehicles as well as for general purpose use The standard covers P FP AFFF and FFFP foam concentrates DEF STAN 42 41 specifies requirements for alcohol resistant foam concentrates for controlling and extinguishing fires where solvents and products containing solvents are bulk stored The standard covers AFFF AR and FFFP AR foam concentrates when used at 6 concentration The International Civil Aviation Authority ICAO specify performance standards for foam concentrates in their document Airport Services Manual Part 1 9137 AN 898 which supports the requirements to be met by Airport Fire Services to be compliant with ICAO Annex 14 Volume one Aerodrome Design and Operations The UK Civil Aviation Authority CAA has adopted the ICAO foam standard in its guidance docu ment Civil Air Publication 168 Licensing of Aerodromes ULI62 covers foam producing equipment and liquid foam concentrates used for the production and discharge of firefighting low expansion foam UL is unique in that it is the firefighting system that is approved including the foam making branch and not the foam co
10. Large scale fire tests have been carried out in the UK to establish whether lead free petrol conform ing with current British and European standards would present any problems to the fire service using their standard low expansion foam equip ment and techniques Reference 7 The results showed that providing brigades follow the Minimum Recommended Application Rates given in this Manual no problems would be expected when using good quality AFFF or FFFP against petrol formulations permitted by current and likely future standards However FP gave poor Firefighting Foam Technical 71 extinction performances against lead free petrols containing oxygenates although its burnback per formances were better than either AFFF or FFFP d Water miscible Class B Liquids Polar solvents and hydrocarbon liquids that are soluble in water water miscible can dissolve nor mal firefighting foams Such liquids include some petrol alcoho mixtures gasohol methyl and ethyl alcohol acrylonitrile ethyl acetate methyl ethyl ketone acetone butyl alcohol isopropyl ether isopropyl alcohol and many others Water miscible class B liquids such as some polar solvents require the use of alcohol resistant type foam concentrates for firefighting and for vapour suppression These foams form a polymer mem brane between the water miscible and the foam blanket which virtually stops the destruction of the foam and allows vapour suppression and
11. Storage at constant low temperatures in the order of 10 C will help to extend the shelf life of foam concentrates When stored under the conditions recommended by the manufacturer most foam concentrates should last at least 10 years and some should remain in good condition for considerably longer The condition of stored foam concentrates should be checked on a regular basis see Chapter 3 Section 3 4 pipe sen Order of Use Wherever possible foam concentrates should be used in the order in which they were manufac tured delivered This will help to prevent prolonged storage of foam concentrates and unwanted effects such as sedimentation and sludge that may occur with age Writing the delivery date on the contain ers is a simple way of keeping track of the age of the foam concentrates Some manufacturers print the date of manufacture on the container labels 2 2 6 Storage Containers and Bulk Storage Manufacturers often advise that their products should be kept in original sealed containers to help to maintain the concentrates in good condi tion These are often 20 or 25 litre cans 200 litre drums or 1000 litre containers If original containers are not used then the advice is to ensure that the storage containers are kept full and sealed to prevent evaporation and oxidisation of the foam concentrate due to the chemical reac tion of the concentrate with air The use of pressure vacuum vents in storage tanks are als
12. e Pre induction Units This system employs two induction units A pre induction unit is installed near a hydrant and draws Firefighting Foam Technical 6l Low Pressure Flexible ring in normal position maximum orifice Controlled flow using 4 5 litres min MARIC valve Fixed regulator set for 4 5 litres min at low pressure Fixed regulator set for 4 5 litres min at high pressure concentrate from a reservoir to produce a concen trate rich solution generally in the region of one part water to two parts foam concentrate This is fed to a specially designed self inducing foam making branch It is at the branch where the required concentration is achieved By using two stages of induction and making use of the pressure and flow from a separate hydrant a much lower pressure loss 1s experienced across the inductor in the branch However the pre induction unit must be accurately matched to the foam mak ing branch When using 75mm diameter hose and large mont tors the distance from a pre induction unit to the monitor can be in excess of 750m f Direct Coupled Water Pump These usually consist of two positive displacement rotary pumps a water motor and a foam concen 62 Fire Service Manual High Pressure Figure 5 24 Principle of operation of one type of metering device Maric valve Flexible ring rolls down tapered seat under pressure decreasing orifice gi
13. foam produced expansion ratios are sometimes in excess of 1000 1 can quickly fill large enclosures Often flexible ducting is required to transport the foam to the fire Due to its volume and lightness high expansion foam is more likely than low and medium expansion foam to break up in moderate ly strong wind conditions Reference 1 The equipment used to produce secondary aspirat ed foam is often standard water type branches and nozzles although there are some specifically designed large capacity nozzles available The foam produced in this way is not well worked see Chapter 4 Section 4 2 has a very low expansion ratio and short drainage time and tends to be very fluid These properties combined with the film forming nature of the foam concentrates used can result in a finished foam blanket that can quickly knockdown and extinguish fires of some liquid hydrocarbon liquid fuels This ability can make them ideal for use in certain firefighting situations such as aircraft crash rescue However the foam blanket tends to collapse quickly so providing very poor security and resistance to burnback Secondary aspirated foam can be thrown over a greater distance than is possible with primary aspi rated low expansion foam This has resulted in equipment being designed specifically to project secondary aspirated foam into large storage tank fires Manufacturers of this equipment recommend the use of film forming foam concentrate typ
14. systems and other equipment Mixing of incom patible foam concentrates is also likely to lead to poor firefighting foam being produced with an associated reduction in firefighting performance Consequently the ground rules to ensure that incompatible foam concentrates are not mixed together are as follows Do not mix together different types grades brands or concentrations of foam concen trate without first consulting the manufac turer s All possible adverse effects such as reduced shelf life formation of sludge reduction in firefighting performance etc should be explored with the manufacturer and understood If the manufacturer s agree to this mixing it is likely that the resulting foam concentrate mixture will tend to exhib it the least effective properties of each of the foam concentrates mixed When changing over from one type of foam concentrate to another especially in bulk storage or fire appliance tanks first ensure that all of the old type has been removed and the tank and equipment have been thor oughly cleaned and dried before refilling Ensure that the new foam concentrate is compatible with the material of manufacture of the storage container The chemical properties of foam concen trates can change with time and storage conditions Consequently even a new batch of the same brand and grade might cause difficulties when mixed with older stock especially if deterioration of the old stock ha
15. those with short drainage times are often referred to as being of poor quality while those that are dry 1 e those with long drainage times are referred to as being of good quality However there is no overall definition of a good quality foam This really depends on which foam is being assessed and its intended use On some fuels AFFFs and FFFPs rely on being wet to assist in the formation of a film on the 9 9 surface and for quick cooling It can also assist in giving them quick control and knockdown capa bilities P and FP finished foams are often better used dry to provide acceptable knockdown and extinction performance and good burnback resis tance If used too wet by applying them via poor foam making equipment for instance these foams are likely to give very poor firefighting perfor mance Applying them too dry will result in very thick foam being produced which does not flow very easily and again results in very poor firefight ing performance As part of the routine checking of the operation of a foam making system expansion ratios and drainage times of the finished foam can be mea sured and compared with previous measurements Figure 4 1 shows the basic principles of measuring low expansion foam expansion ratios and drainage times The current British Standards for foam con centrates see Chapter 3 should be referred to for exact details of equipment and test me
16. 3 4 Most physical property tests are relatively simple and inexpensive to perform Consequently manu facturers are more likely to carry out physical property tests than carry out fire tests as part of their quality control procedures However physi cal property tests do not provide any useful infor mation regarding the firefighting performance of foam concentrates A wide range of physical property tests are carried out as part of standard approvals processes the fol lowing physical property tests are most often included 3 2 2 Specific Gravity Relative Density Specific gravity or relative density is a measure of the ratio of the mass of a given volume of foam con centrate to the mass of an equal volume of water This is normally measured with the temperature of the foam concentrate and water at 20 C Specific gravity can be used to determine whether a foam concentrate has been diluted or over concentrated 3 2 3 pH acidity alkalinity pH is a measurement of the acidity to alkalinity of a liquid on a scale of to 14 A pH of 7 is neutral e g pure water a pH of is very acidic a pH of l4 is very alkaline Measurements of pH help to give an indication of the corrosion potential of the liquids Section 2 2 3 3 2 4 Sediment Sludge Sediment is a measure of the amount as a percent age by volume of undissolved solids contained in the foam concentrate Sediment is also sometimes known as sludge Excess
17. 64 64 64 64 65 65 vil 55 5 5 2 5 5 0 General Refractometer Method Flow Method Chapter 6 Categories of Fire and the Use of Firefighting Foams 6 1 6 1 1 6 1 2 6 1 3 6 1 4 6 2 6 3 6 3 1 6 3 2 6 3 3 6 3 4 6 3 5 6 3 6 Against Them Classes of Fire Class A fires Class B Fires a General b High Flash Point Water immiscible Class B Liquids c Low Flash Point Water immiscible Class B Liquids d Water miscible Class B Liquids Class C Fires Class D Fires Electrical Fires Types of Liquid Fuel Fire General Spill Fires Pool Fires Spreading Fires Running Fires Other Terms Chapter 7 Application Rates 71 General 12 Critical Application Rate 73 Recommended Minimum Application Rate 7 3 1 General 7 3 2 Fires Involving Water immiscible Class B Liquids 7 3 3 Fires Involving Water miscible Class B Liquids 7 4 Optimum Application Rate 73 Overkill Rate 7 6 Continued Application Rate References Further Reading Glossary of Terms Firefighting Foams Vill Fire Service Manual 65 66 66 69 69 69 70 70 71 71 12 72 72 72 72 I2 73 173 73 74 74 i 15 75 75 75 19 17 rz 71 78 79 80 1 Firefighting Foam Technical Firefighting Foam Technical Chapter Chapter 1 Introduction 1 1 General Firefighting foams have been developed primarily to deal with the hazards posed by liquid fuel fires Water is used for most
18. FFFP FP P and SYNDET are Newtontan liquids The application by any appropriate means of a firefighting liquid that does not mix the liquid with air to produce foam i e aspiration does not occur The term non aspirated foam is often used incorrectly to describe the product of a foam solution that has been passed through equipment that has not been specifically designed to produce foam such as a water branch However the use of this type of equipment will often result in some aspiration of a foam solution This is because air is usually entrained into a jet or spray of foam solution as it leaves the branch as it travels through the air due to the turbulence produced by the stream and or when it strikes an object This causes further turbulence and air mixing There is sufficient air entrained by these processes to produce a foam of very low expansion often with an expansion ratio of less than 5 1 Consequently the term secondary aspirated foam is preferred in these cases see alSo primary aspirated and secondary aspirated foam As the rate of flow of non Newtonian pseudo plastic liquids increases their viscosity decreases and so they flow more easily Consequently getting them to flow initially can be difficult but once flowing their viscosity reduces to a more acceptable level Many alcohol resistant foam concentrates such as AFFF AR and FFFP AR are considered to be non Newtonian pseudo plastic liquids Oil repellent
19. For Checking Foam Solution Concentration as Produced by Foam making Equipment 5 5 1 General It is important that the whole foam making system is regularly checked to ensure that it works as expected and that the concentration of the foam solution produced is as required The following two methods can be used to check the concentra tion of foam solution The use of a refractometer Foam concentrate and water flow measurements On first inspection it would appear that the refrac tometer method is perhaps too difficult to use However once some experience has been gained in its use the refractometer method will prove Firefighting Foam Technical 65 more accurate and simpler to use than attempting to measure liquid flows especially if relatively accurate flowmeters are not available 55 2 Refractometer Method One method of checking the concentration of the foam solution is by the use of a refractometer When used for this application a refractometer measures the change that occurs in the direction of travel of light at the junction of foam solution with glass in terms of its refractive index There ts a Straight line relationship between refractive index and solution concentration A refractometer looks similar to a small telescope with an eyepiece at one end and a hinged prism box at the other They are available from laborato ry suppliers and are relatively easy to use with care They are widely used in manuf
20. combustion The vigorous application of emulsifiers directly to fires in petro leum based fuels is claimed by the manufacturers to result in rapid control and extinction In addi tion because the fuel molecules have been encap sulated they say that it is unlikely that re ignition will occur Emulsifiers have only recently been introduced and their performance relative to other foam concentrates and firefighting media has yet to be proven in the UK 4 6 Edge Sealing The term edge sealing relates to the ability of a foam blanket to seal against hot metal surfaces Hot metal surfaces can cause breakdown of a foam blanket due to the boiling off of its water content and increased vapour release from the fuel at the hot surface This can result in the inability of a fin ished foam to fully extinguish fires at this interface 30 Fire Service Manual Foams which have a good resistance to heat tend to exhibit good extinguishing performances and burn back resistance and therefore should have good edge sealing properties However when hot metal surfaces i e in excess of 100 C are encoun tered by a foam blanket destruction of the foam blanket is inevitable and steps should be taken where possible to cool these surfaces sufficiently to ensure edge sealing can take place This can be particularly important when fighting large tank fires 4 7 Foam Blanket Stability Drainage Time Drainage time is a measurement of the rate at which fo
21. e the worst case situation Forceful application is far more testing of the firefighting capabilities of the foam particularly its fuel tolerance Some standards specify that the foam making branch should be in a fixed position others allow it to be hand held Fixed branches are more likely to result in a repeatable fire test while the hand held branch is more realistic However hand held applications can result in variations in firefighting performance that can be attributed more to the Operators experience and tactics than the proper ties of the foam alone Fixed branches have the disadvantage that fire tests involving them will tend to favour the more fluid foams Generally the test equipment used during standard fire tests makes finished foams that have lower Firefighting Foam Technical 21 expansion ratios and much longer drainage times Consequently the foams produced are not realistic because they are more stable and better worked see Chapter 4 Section 2 than foams produced through fireground foam making equipment The test equipment only produces primary aspirat ed foam for use during the standard fire tests referred to in this Chapter of the Manual there are currently no standards available for directly deter mining the suitability of foam concentrates for fire service secondary aspirated use Under What Conditions are the Fire Tests Performed 3 3 8 Fuel foam solution air and fuel temperatu
22. factors involved in the manu facturing process To complicate this even further some manufacturers produce different grades of the same foam concentrate type for different mar kets and obviously for use at different concentra tions Consequently the information contained within this Chapter gives an indication of the typical char acteristics of each of the main types of foam con centrate Good quality foam concentrates may have better characteristics those of poor quality foam concentrates may be considerably worse These characteristics will in any case vary depending on the equipment and tactics used the size and type of incident and the fuel involved Some foam concentrate standards can help to dis tinguish good from bad quality products for certain applications However these standards need to be closely scrutinised to ensure that they meet the wide range of fire service requirements see Chapter 3 8 Fire Service Manual This Chapter provides information on each of the different types of foam concentrate and water additives mentioned above Information is also given on the storage and handling characteristics of foam concentrates However the manufacturers should always be consulted regarding the suitabil ity of materials used for the storage and handling of their products Protein Based Foam Concentrates 2 1 2 a Protein P Protein foam concentrates are liquids that contain hydrolysed protein with t
23. firefighting incidents However it is generally ineffective against fires involving flammable liquids This is because water has a density that is greater than most flammable liquids so when applied it quickly sinks below their surfaces often without having any significant effect on the fire However when some burning liquids such as heavy fuel oils and crude oils become extremely hot any water that 1s applied will begin to boil The resulting rapid expansion as the water converts to steam may cause burning fuel to overflow its containment and the fire to spread this event is known as a slop over Also the water that sinks below the fuel will collect in the container and should the container become full this will result in the fuel overflowing Finished firefighting foams on the other hand consist of bubbles that are produced from a com bination of a solution of firefighting foam concen trate and water that has then been mixed with air These air filled bubbles form a blanket that floats on the surface of flammable liquids In so doing the foam suffocates the fire and can lead to the knockdown and extinction of the flames The low density of firefighting foam blankets also makes them useful for suppressing the release of vapour from flammable and other liquids Special foam concentrates are available which allow vapour suppression of many toxic chemicals Water miscible liquids such as some polar sol vents can pos
24. flow rate to maintain the required foam concentration d Injection in to Pump Inlet Injection in to pump inlet systems as the name suggests involves the injection of foam concen trate in to the eye of the pump Injection is usually either by electric pump or by gravity feed For an electric pump system a regulator is used to control the amount of foam concentrate that can enter the high pressure side of the pump Consequently this can be calibrated to allow vari ous concentrations of foam concentrate to be used through one or two hosereels or a main line branch if necessary In the gravity fed systems precisely sized orifices are used to regulate the supply of foam concentrate into the pump Several orifices of different sizes can be included in the system These also allow different concentrations of foam concentrate to be used or for one or two hosereel branches or a main branch to be used in conjunction with the system e In line Inductors Hosereel in line inductors work in the same way as the main delivery types previously described in Section 5 3 of this Chapter However tests carried out on one hosereel in line inductor Reference 8 found that there was a pres sure loss in excess of 50 across the inductor 64 Fire Service Manual when the recommended jet spray branch was oper ated on jet When the branch was operated on spray the pressure loss across the inductor was in excess of 70 and when the effec
25. foam in contact with the liquid forms an icy slush which insulates and protects the upper layers of foam and which in turn acts by reducing the evaporation rate from the liquid A further important advantage is the relatively low amount of heat transmitted to the liquid by water draining from medium and high expansion foams Low expansion foam is not suitable since it increases the rate of evaporation from the liquid For a liquefied gas spillage any reduction in the rate of evaporation of the liquid is beneficial in that it limits the size of the flammable or explo sive cloud generated and hence reduces the possi bility of ignition 6 1 4 Class D Fires Class D fires are those which involve combustible metals such as magnesium titanium zirconium sodium potassium and lithtum Firefighting foams should not be used with water reactive metals such as sodium and potassium nor with other water reactive chemicals such as triethyl aluminium and phosphorous pentoxide Other metal fires are treat ed as class A fires but in general the use of media other than foam or water is found to be more suit able 6 2 Electrical Fires Firefighting foams are unsuitable for use on fires involving energised electrical equipment Other extinguishing media are available Fires in de energised electrical equipment are treated as either class A or B as appropriate see above 6 3 Types of Liquid Fuel Fire 6 3 1 General The classes of fire d
26. in identifying matched equipment This Section also includes information on methods that can be used to check the concentration of the foam solution that is produced by foam making systems 3 2 In line inductors An in line inductor 1s placed in a line of delivery hose usually not more than 60 metres away from the foam making equipment This allows the foam making equipment to be moved around rela tively freely without the additional need to move foam concentrate containers In line inductors employ the venturi principle to induce the concentrate into the water stream Note self inducing foam making branches also usually work in this way Water is fed into the inlet of the inductor generally at a pressure of around 10 bar see Figure 5 14 This passes through the smaller diameter nozzle within the inductor to a small induction chamber and then to on the inductor s large diameter outlet via a flow improver As the water enters the small nozzle its velocity increases dramatically causing its pressure to drop the venturi principle and the pressure in the induction chamber to fall below atmospheric pressure This partial vacuum sucks the foam concentrate through the pick up tube and into the low pressure induction chamber Firefighting Foam Technical 5 Foam concentrate Non return Water instantaneous inlet Figure 5 14 Principle of operation of an inline inductor A non return valve a ball i
27. it seconds Induction rate of inductor percent Flow rate of foam concentrate lpm Flow rate through foam making equipment Iom The flow rate through the foam making equipment should if possible be measured with a flowmeter If a flowmeter is not available then the flow rate information provided by the manufacturer will have to be used although this may not be particu larly accurate for normal fire service operating conditions The following is an example of the use of the above calculation A LX foam making branch operates with an in line inductor at 225 litres per minute at a branch pressure of 7 bar The inductor was timed to pick up 5 litres of foam concentrate in 45 seconds The induction rate of the inductor is calculated as follows Flow rate of foam concentrate 5 x 60 45 6 7 Ipm Induction rate of inductor 6 7 x 100 225 3 0 Firefighting Foam Technical 67 Q Firefighting Foam Technical Chapter Chapter 6 Categories of Fire and the use of Firefighting Foams against them 6 1 Classes of Fire In the UK the standard classification of fire types is defined in BS EN 2 1992 as follows Class A fires involving solid materials usually of an organic nature in which combus tion normally takes place with the for mation of glowing embers Class B fires involving liquids or liquefiable solids Class C fires involving gases Class D fires involving metals
28. it strikes an object This causes further turbulence and air mixing There is sufficient air entrained by these processes to produce a foam of very low expansion often with an expansion ratio of less than 4 1 To more accurately describe the different types of finished foam produced the terms primary or secondary aspirated are preferred Primary aspirated foam finished foam that is produced by purpose designed foam making equipment Secondary aspirated foam finished foam that is produced by all other means usually standard water devices Secondary aspiration will normally result in a poor quality foam being produced due to insufficient agitation of the foam air mixture That 1s to say the foam will generally have a very low expansion ratio and a very short drainage time see below However foam blankets with short drainage times can be advantageous if rapid film formation on a fuel is required see Chapter 4 Section 4 4 It is highly unlikely that a foam solution can be applied operationally to a fire in such a way that no aspiration occurs However should such circum stances occur then this would be referred to as a non aspirated application Some water additives such as wetting agents may be formulated so that they do not foam use of these types of additive would result in non aspirated application even through purpose designed foam making equipment 1 5 Foam Expansion Ratios 1 5 1 Ge
29. longer the foam making tube the better the working and mixing of foam solution with air This results in a more stable finished foam with drainage times that are longer than those produced by shorter foam making branches Large scale petrol fire trials have been carried out Reference 7 where the firefighting performance of a short LX foam making branch approximate length 0 5m and a longer LX foam making branch approximate length 0 8m were compared When these fires were fought with film forming foam concentrates both types of branches Firefighting Foam Technical 4 Table 5 1 LX foam making branches comparison of foam properties of long and short LX foam making branches Foam Foam Flow Expansion 25 drainage time making concentrate lpm branch Short AFFF iy 5 17 1 Lmin 43seeq Long AFFF 225 15 7 2min 35secs Short AFFF AR 225 14 2 3min 15secs Long w AFFF AR 2y 13 4 6min 4 secs Short FFFP 225 11 9 54secs Long FFFP 25 H7 ain Short FP 225 98 Imin l Long pooo 225 11 6 Imin l 5sec Notes to Table 5 1 Measurements taken form References 5 and 7 produced foams that gave simular knockdown and extinction times but the foam produced by the longer foam branches had much longer drainage times and gave significantly better burnback pro tection During these same fire tests it was found that the firefighting performance of FP foam was extreme ly poor when used through the short foam making branc
30. lpm and the by pass open the foam output is claimed to be 155 m min of finished foam with an expansion ratio of between 800 and 1200 1 Figure 5 10 Essential principles of a High Expansion Foam Generator Ducting Figure 5 1 A typical high expansion foam generator DEC Figure 5 12 Large HX foam generator stowed E A on foam tender right g Large plastic bins centre are for decanting foam Photo Northern ireland Fire Brigade WEC ducting Turbine shown dotted Control for shutting off water supply to discharge nozzles Rear View with fan duct removed By pass control to be in fully open position to discharge all water after passing through turbine Water discharge Plan View female coupling inlet Firefighting Foam Technical 49 One typical small water turbine driven HX foam generator weighs 16 kg and is claimed by the manufacturer to produce at 7 bar inlet pressure with a nominal flow of 245 Ipm 80 m min of fin ished foam with an expansion ratio of 330 1 5 3 Foam Concentrate Induction and Injection Equipment 5 3 1 General Foam concentrate induction and injection equip ment is used to introduce foam concentrate into the water supply in order to produce foam solution There is a need for this equipment to work accu rately in order to avoid wastage of foam concen trate and more importantly to help to
31. of the hose between the generator and branch and the size of the branch need to be carefully selected Such generators are used to a limited extent in the Fire Service A typical example has a recommend ed water inlet pressure of 10 5 bar and a nominal water requirement is 255 lpm It can be used with up to 60 m of 70 mm hose and a water branch with a 38 mm nozzle Larger sizes of generator are made but are generally used in fixed installations Firefighting Foam Technical 43 e Figure 5 Model 5A low expansion foam generator 5 2 5 LX Foam Monitors Primary aspirating LX foam monitors are larger versions of foam making branches which cannot be hand held They may be free standing and portable mounted on trailers or mounted on appli ances They usually have multiple water connec tions and may be self inducing or used in con junction with one of the induction methods described in Section 5 3 below They can also be found in fixed installations at oil tanker jetties and refineries or as oscillating monitors in aircraft 44 Fire Service Manual 610 mm Air inlet hangars Similar monitors are fitted to airport foam tenders often with adjustable jaws which allow the option of a flat fan shaped spray There are numerous LX foam monitors in use coming in a wide range of nominal flow and inlet pressure requirements One example has a nominal flow requirement of approximately 1800 lpm at an in
32. sediment can result in blockages and other serious problems with induc tion systems and other equipment 3 2 5 Spreading Coefficient Film forming foam concentrates are formulated to form an aqueous film on the surface of some hydrocarbon liquids Spreading coefficient is a measure of this ability This is determined in a laboratory by measuring the surface tensions of a solution of the foam con centrate and a hydrocarbon liquid normally cyclohexane In addition the interfacial tension is also determined by measuring the surface tension where the foam solution top and the hydrocarbon liquid bottom meet A calculation is then performed to determine the spreading coefficient of the foam solution The calculation is as follows Spreading coefficient Surface tension of the foam solution minus Surface tension of the hydrocarbon liquid minus nterfacial tension If the spreading coefficient is positive the foam solu tion will form an aqueous film on that particular hydrocarbon liquid and the foam concentrate is deemed to be film forming If the spreading coeffi cient is negative an aqueous film will not be formed and the foam concentrate is not film forming Note that although a solution of the foam concen trate may form a film on cyclohexane or what ever Firefighting Foam Technical 19 hydrocarbon liquid used this does not necessarily mean it will form a film on this or any other hydro carbo
33. suitability of a foam concentrate for a particular task the manu facturer of the foam concentrate should be con sulted to ensure that it can be used safely and successfully 2 16 Wetting Agents Wetting agents are liquids which when added to water in the required proportion reduce the surface tension of the water and increase its Firefighting Foam Technical 1 penetrating and spreading abilities They may also provide emulsification see Section 2 1 8 below and foaming characteristics Dedicated wetting agents are available although some manufacturers of film forming and SYNDET foam concentrates state that these too may be used as wetting agents Dedicated wetting agents are generally used at concentrations of up to 1 In addition some film forming and SYNDET foam concentrates intended for use at 3 on hydrocarbon fuel fires can be used as wetting agents at concentrations of between 0 5 and 3 0 Wetting agents are generally rec ommended for use in either non aspirated or sec ondary aspirated application through standard water branches Some dedicated wetting agents are also recom mended for use on class B fires Some limited tests Reference 3 have indicated that they are unsuit able for this type of application 2 1 7 Class A Foam Concentrates The term Class A Foam originated in the USA and is used to describe foam concentrates that are primarily intended for use on class A fires They have been in us
34. supply Spillages can also occur and the logistics of keeping the dams topped up need to be considered Debris may also enter the dams which may lead to block ages of the induction system Since the pick up system requires the con centrate container to be positioned very near to the inductor it may not be possible for a bulk supply to be positioned close r T enough to supply the inductor directly ed a Linkage Control pressure to control valve Downstream tapping Valve disc positioned by control valve From hydrant Even at smaller incidents where it is practicable to use foam concentrate drums it may be impossible to determine when the concentrate is about to run out This could lead to water being discharged onto the fire This may also occur whilst the pick up tube is being transferred when a container becomes empty Some firefighters adapt foam concentrate con tainers by cutting off the top so that the contents Firefighting Foam Technical 57 1 x 900 litres min inductor fitted with 27 litres min metering valve Foam solution to branchpipes 2 x 450 litres min inductors fitted with 13 5 litres min metering can be seen and topping up is made easier However this should be done with care because swarf produced when cutting off the tops can be picked up and can cause blockages of the induc tion system To overcome all of the above difficulties many
35. support of an effec tive risk assessment at the commencement of an incident is of the utmost importance to ensure that the correct foams equipment and tactics are selected and employed 2 Fire Service Manual 1 2 Historical Development of Firefighting Foams 1877 Chemical foam first patented by a British scientist 1904 First successful use of chemical foam Used to extinguish an 1 metre diameter naphtha storage tank fire in Russta Foam produced from mixing together large quantities of two chemical solutions 1914 Austrian engineers produce foam by introducing a powder into running water 1920s Protein foam concentrate first produced O along with equipment designed for the production and delivery of this first mechanical foam 1930s Development of early chemical foams with alcohol resisting properties The concepts of aspiration and proportioning were developed for mechanical foam systems much as we know them today Experimental work started on synthetic types of foam concentrate 1940s 3 Protein foam concentrates developed to offer space and weight savings over the exist ing 6 concentrates 1950s Low medium and high expansion foams could now be produced from a single synthetic foam concentrate First water miscible liquid resistant mechanical foam concentrate developed 1960s Fluoroprotein and AFFF Aqueous Film forming Foam foam concentrates developed Improved a
36. systems fixed on to appliances this requires the appliance to be taken off the run However one of the major advantages of round the pump proportioners is that their use does not result in pressure losses at the output side of the pump Rotating throat Foam solution outlet Ki J i Foam concentrate intet Flow scale 1 min Firefighting Foam Technical 55 To summarise the advantages of round the pump proportioners are relatively inexpensive although more expensive than in line inductors they can provide a variable accurate induction flow rate over a wide range can be used as a fixed or temporary system on appliances wide operating pressure and flow range do not cause the pressure drops in the delivery hose that are associated with in line inductors this allows foam solution to be supplied through extended lengths of hose The disadvantages are to maintain accurate concentration of foam concentrate the operator must continually calculate and adjust the foam concentrate flow rate foam solution is passed through the pump There 1s concern regarding corrosion of the pump and other associated areas thorough flushing after use is essential where the pump feeds more than one branch there is a need to match the pump output and the concentrate flow to take account of the number of branches in use at any one time pressure control valves are needed where water feed into
37. tackle class A fires AFFF foam concentrates are not recommend ed for the production of high expansion foam AFFF foam concentrates are of similar cost to FFFP foam concentrates AFFF is widely accepted for crash rescue fire fighting uses and on less volatile fuels such as kerosene and diesel oil It is widely used offshore secondary aspirated for helideck protection at a concentration of 1 Problems have been experienced when attempting to extinguish fires involving liquids with high vapour pressures such as hexane and high octane petrol where quantities of vapour have penetrated thin very low expansion secondary aspirated AFFF foam blankets AFFF foam concentrate is not particularly corro sive and contains no special corrosion inhibitors However its surface active agent content causes the concentrate to be more searching than water and therefore more corrosive Materials that should be considered for materials for storage con tainers and handling equipment are stainless steel GRP epoxy lined carbon steel and polyethylene Alcohol Resistant Foam Concentrates AFFF AR and FFFP AR 2 1 4 Alcohol resistant foam concentrates have been developed to deal with fires involving water mis cible liquids such as alcohols and some petrol blends containing high levels of alcohols and other similar fuel performance improvers 10 Fire Service Manual Two types of alcohol resistant foam concentrate are in genera use in the
38. the storage of the P FP FFFP and FFFP AR foam con centrates but was acceptable for the AFFF types Aluminium was found to be an excellent material for the storage of the AFFF type foam concentrates but unacceptable for any of the others GRP and epoxy coated materials were found to be accept 14 Fire Service Manual able for all but the SYNDET foam concentrate which produced severe damage in both materials in particular it caused the epoxy coating to peel away from the underlying steel The effects of corrosion will not only lead to the gradual or sometimes rapid destruction of the storage containers but it may also lead to serious chemical effects on the foam concentrates them selves possibly leading to poor foam production and firefigbting performance The corrosion and chemical effects can take many forms but a particularly serious consequence can be the formation of particles and very viscous products sludge in the foam concentrate These effects can lead to blockages and other serious problems with induction systems and other equip ment 2 2 4 Storage and Use Temperature Conditions Many P FP AFFF and FFFP foam concentrates are freeze protected for low temperature storage and use Some manufacturers state that some of their foam concentrates can be used when they are at temperatures as low as 29 C Some manufacturers produce both freeze protected and non freeze protected versions of their foam concentrates C
39. the United Kingdom for The Stationery Office TJ763 4 00 C50 5673 Firefighting Foam Technical Preface This manual Volume 1 Fire Service Technology Equipment and Media Firefighting Foam deals with technical aspects of foam concentrates stan dards and equipment This book complements the existing manual in Volume 2 Fire Service Operations Firefighting Foam These books replace The Manual of Firemanship Book 3 Part 3 Dear Chief Fire Officer Letter 2 97 Foam Application Rates The Home Office is endebted to all those who have helped in the preparation of this work in particular Mr Bryan Johnson BSc Home Office Fire Experimental Unit Mid and West Wales Fire Brigade Angus Fire Armour Ltd Williams Fire and Hazard Control Inc Civil Aviation Authority British Fire Protection Association Ltd Cheshire Fire Brigade London Fire Brigade Fire Service College Dr Tony Cash Northern Ireland Fire Brigade Home Office April 2000 Firefighting Foam Technical ill Firefighting Foam Technical Contents m a Preface Chapter 1 Introduction 1 1 General 1 1 2 Historical Development of Firefighting Foams 2 1 3 How Foams Extinguish Fires 3 1 4 Production of Finished Foam 3 1 4 1 General 3 1 4 2 Percentage Concentration 3 1 4 3 Aspiration 4 1 5 Foam Expansion Ratios 5 1 5 1 General 5 1 5 2 Equipment Used For Generating Different Expansion Ratio Fo
40. the suction side of the pump is high see below there are very small orifices within the system which can easily be blocked by debris or foam concentrate sludge 5 3 4 Pressure Control Valves A round the pump proportioner will only func tion correctly if the pressure on the suction side of the pump is less than one third of the pressure on the delivery side If this limit is exceeded when pumping from a hydrant for instance the back pressure acting on the outlet of the propor tioner will be sufficient to inhibit the induction of foam concentrate In extreme conditions where no non return valves are present water may feed back into the foam concentrate con tainer 56 Fire Service Manual To prevent this situation from arising a pressure control valve may be used with the proportioner The valve reduces the pressure in the pump inlet line to one fifth of the incoming pressure thus bringing it within the required limit under most of the operational conditions that are likely to be encountered The valve may be fitted as an integral part of the pipework system on an appliance or used as a portable unit inserted into the pump inlet line at any convenient position Figure 5 19 illustrates a typical pressure control valve Water under pressure from the hydrant passes through the valve over a movable butterfly This butterfly is connected to a hydraulic piston which receives pressure from both sides of the but terfly The a
41. these foams to water miscible fuels suitable for subsurface base injection They must not be used for base injection into water miscible fuels When used on non water miscible fuels control and extinction times are similar to those of conventional AFFF and FFFP foams with burnback performance similar to that of FP Extinction and burnback performance is considerably better when used primary aspirated 1 e using a foam making branch than when used secondary aspirated i e using a water branch very stable foam blankets with slow foam drainage times good at sealing against hot metal objects good burnback resistance good vapour suppression and the following disadvantages care is required in selecting the correct rate of induction due to the need to use at 3 concentration for hydrocarbon fuels and at 6 for water miscible fuels However some alcohol resistant foams are available that may be used at the same induction rate normally 3 for both hydrocarbon and water miscible fuels 4 15 Environmental Impact of Firefighting Foams 4 15 1 General Firefighting foams are the most effective means of extinguishing most liquid fuel fires In doing so they greatly reduce fire spread the air pollution potential of a fire and the amount of water that needs to be used to tackle the fire This in turn reduces the amount of contaminated water pro duced during firefighting operations and the environmental
42. 1992 6 SRDB Publication 9 87 Pilot Study on Low Expansion Foam Making Branchpipes B P Johnson P L Parsons 1987 7 SRDB Publication 22 88 Additives for Hosereel Systems Preliminary Trials of Foam on Small Scale lsopropanol Fires B P Johnson 1988 8 FRDG Publication 5 91 Additives for Hosereel Systems Trials of Foam On Tyre Fires B P Johnson 1991 80 Fire Service Manual FRDG Publication 4 94 A Comparison Of Various Low Expansion Foams When Used Against The Proposed ISO And CEN Standard Medium Scale 4 5M Hydrocarbon Fuel Test Fire B P Johnson 1994 Firefighting Foam Technical Glossary of Terms Firefighting Foams Note Not all of these terms have been used in this Manual of Firemanship but they have been included here for completeness Accelerated ageing Storage of foam concentrate at high temperatures to indicate long term storage properties of the foam concentrate at ambient temperatures Acidity See pH Alcohol resistant These may be suitable for use on hydrocarbon fuels and foam concentrates additionally are resistant to breakdown when applied to the surface of water miscible liquid fuels Some alcohol resistant foam concentrates may precipitate a polymeric membrane on the surface of water miscible liquid fuels Alkalinity See pH Application rate The rate at which a foam solution is applied to a fire Usually expressed as litres of foam solution per square metre of the fire surfa
43. 7 bar outlet pressure Typical sizes of inductor are 225 lpm 450 lpm and 900 lpm Consequently an inductor designed for a flow of 450 Ipm can be used with one foam mak ing branch requiring 450 ipm or two foam making branches each requiring 225 Ipm and so on It is important to note however that only one inductor should be used in any one hoseline For Instance two 225 lpm inductors must not be used in a Single hoseline to supply a 450 lpm foam making branch If this were to happen the combi nation of the pressure losses across each of the inductors would result at best in the delivery to the foam making branch of a very low pressure and low flow foam solution of incorrect concen tration Some inductors contain a bypass valve see Figure 5 14 which assists in enabling them to maintain induction over a range of inductor inlet pressures often 4 to 10 bar when using the correct foam making equipment In addition the bypass valve can help to minimise the pressure drop across the inductor and assist in overcoming some slight mis match problems caused by using inductors and foam making equipment of similar nominal flowrates but from different manufacturers However the accuracy of inductors containing bypass valves can vary considerably with pressure although they will tend to be slightly more accu rate at varying pressures than those without bypass valves see below Other inductors without the bypass will o
44. A liquid with a specific gravity of less than one will float on Water immiscible liquid A liquid that is not soluble in water water unless it is water miscible a specific gravity of more than one indicates that water will float on top of the liquid Water miscible liquid A liquid that is soluble in water Polar solvents and hydrocarbon liquids that are water miscible can dissolve normal firefighting Spill fire A flammable liquid fire having an average depth of not more foams see also alcohol resistant foam concentrates than 25mm Wetting agent A chemical compound which when added to water in correct Stability The ability of a finished foam to retain shape and form particu proportions materially reduces its surface tension Increases Its penetrating and spreading abilities and may also provide foaming larly in the presence of heat flame and or other liquids The 25 characteristics drainage time is often used as a measure for stability Subsurface injection See base injection Surface active agents A chemical ingredient of some foam concentrates Finished foams is stabilised by the addition of surface active agents or surfactants which promote air water stability by reducing the 4 liquids surface tension Most surface active agents are organic in nature and common examples are soaps and detergents Synthetic detergent These are based upon mixtures of hydrocarbon surface active SYNDET foam agents and may contain fluorinated su
45. LX foam making branches and monitors have been produced Some large output primary and secondary aspirat ing monitors are described in Volume 2 of the Manual These are primarily meant for applying foam to storage tanks The foam solution supply rates for these monitors can be in excess of 40 000 litres per minute In general the means of distinguishing between the capacities of different foam making equipment is either by the nominal flow requirement of the equipment litres per minute lpm and or the vol ume of the foam produced cubic metres per minute m min Usually for LX foam making Figure 5 1 FBSx MkII 225 litres min foam solution at 5 5 BAR Photo Mid and West Wales Fire Service 40 Fire Service Manual Figure 5 2 F450 450 litres min of foam solution at 7 BAR Photo Mid and West Wales Fire Service equipment it is the nominal flow requirement only that is used to classify them The use of this classi fication also aligns with application rates see Chapter 7 which recommend the minimum amounts of foam solution in litres per minute that should be applied to each square metre of fire area lpm m7 For MX and HX foam making equipment both the nominal flow requirement and the volume foam production are used to classify their output Generally the volume foam production figures specified by manufacturers will be those achieved when using SYNDET foam concentrates However film forming foams may a
46. Specification for high expansion foam concentrates for surface application to water immiscible liquids Specification for low expansion foam concentrates for surface application to water immiscible liquids Specification for low expansion foam concentrates for surface application to water miscible liquids Fire Extinguishing Media Foam Concentrates International Standards Organisation Specification for low expansion foam concentrates for top application to water immiscible liquids Specification for medium and high expansion foam concentrates for top application to water immiscible liquids Specification for low expansion foam concentrates for top application to water miscible liquids Foam Liquids Fire Extinguishing Concentrates Foam Fire Extinguishing UK Ministry of Defence Foam Liquids Fire Extinguishing Concentrates Alcohol Resistant Foam Fire Extinguishing UK Ministry of Defence Licensing of Aerodromes Chapter 8 Appendix 8E Foam Performance Levels Specifications and Test Procedures UK Civil Aviation Authority Foam Equipment and Liquid Concentrates USA Underwriters Laboratories Fire Extinguishing Agent Aqueous Film forming Foam AFFF Liquid Concentrate For Fresh and Sea Water USA Military Navy Firefighting Foam Technical 17 Each of these standards has been produced 1n order to ensure the quality of particular foam concen trates for particular purposes The British
47. This process also produces steam which dilutes the oxygen around the fire 1 4 Production of Finished Foam 1 4 1 General Finished foam is produced from three main ingre dients foam concentrate water and air There are usually two stages in its production The first stage is to mix foam concentrate with water to produce a foam solution The foam concentrate must be mixed into the water in the correct pro portions usually expressed as a percentage in order to ensure optimum foam production and firefighting performance This proportioning 1s normally carried out by the use of inductors or proportioners or other similar equipment This results in the production of a premix foam solu tion In other words the foam concentrate and water have been mixed together prior to arriving at the foam making equipment Occasionally premix solutions are produced by mixing the cor rect proportions of water and foam concentrate in a container such as an appliance tank prior to pumping to the foam making equipment In addi tion some types of foam making equipment are fitted with a means of picking up foam concen trate at the equipment these are known as self inducing with the mixing taking place in the foam making equipment itself The second stage is the addition of air to the foam solution to make bubbles aspiration to produce the finished foam The amount of air added depends on the type of equipment used Hand held foam
48. UK fire service those based on synthetic aqueous film forming foams AFFF AR and those based on film forming fluo roprotein foams FFFP AR Alcohol resistant foams can also usually be used on hydrocarbon fuels and because of this are sometimes known as multi purpose foams Non alcohol resistant foam concentrates 1 e P FP FFFP SYNDET and AFFF are not suitable for use on water miscible liquids because their finished foam blankets quickly disintegrate on contact with these liquids This happens because the water con tained in the foam rapidly mixes with and 1s extracted by the water miscible liquids causing the foam to quickly break down and disappear AFFF AR and FFFP AR foam concentrates con tain a polymeric additive which rapidly falls to the surface of a water miscible liquid when the fin ished foam comes into contact with it The poly meric additive forms a tough skin also known as a raft or membrane on the surface of the liquid Once formed the water miscible liquid cannot penetrate this skin and is hence unable to attack the finished foam above it conventional foams cannot form these water miscible liquid resistant skins It should be noted that the polymeric membrane 1s not formed when alcohol resistant foams are applied to hydrocarbon fuels It is also important to note that although AFFF AR and FFFP AR fin ished foams form aqueous films on some liquid hydrocarbon fuels it is not possible for t
49. ace injection need to have a high tolerance to fuel con 3 2 Fire Service Manual tamination otherwise the foams would burn away immediately on contact with the flames on the sur face of the product Subsurface injection can only be used in tanks containing certain hydrocarbon fuels it cannot be used for tanks containing water miscible fuels because even with alcohol resistant foams these fuels will destroy the foam blanket on contact and a foam blanket will not form In addition this will mean that the polymeric skin cannot form on the surface of the fuel see Chapter 2 Section 2 1 4 FP FFFP FFFP AR AFFF and AFFF AR foams are generally considered suitable for base injec tion 4 12 Quality of Finished Foam The production of good quality finished foam depends on the use of a suitable type and quality of foam concentrate for the task in hand foam concentrate in good condition due to correct storage foam concentrate used at the correct concentration good design and choice of equipment good maintenance of equipment correct pump pressure and foam solution flow for the equipment in use Drainage times and expansion ratios and some times shear strength can be measured and com pared to provide an immediate indication of the quality of a finished foam Often firefighters will look at and feel the finished foam produced by their equipment and give an immediate assessment of its quality Wet foams i e
50. acturing industries for measurements of concentrations of fruit juices battery acids wines soft drinks starches glues and so on The procedure for using a refractometer is as fol lows a calibration curve should be produced for the foam concentrate under test Ideally this should be produced prior to each occasion that the refractometer is used It is important that the actu al foam concentrate that will be passed through the system and water from the same supply be used to make up samples of various concentrations of foam solution At least 3 calibration points should be chosen which cover the range of from 0 5 times to 2 times the expected inductor pick up concentration For instance for a system supplying 3 concentrate as a 3 foam solution the calibration samples should be 1 5ml 3ml and 6ml respectively of 3 foam concentrate made up and thoroughly mixed with water each to make 100ml of foam solution Le these would produce 1 5 3 and 6 foam solu tion samples The refractive index of each of these should be measured using the refractometer and a graph plotted of refractive index against percent age concentration All of the calibration points should then be joined with a straight line The foam making system should then be run up to its normal operating conditions A sample of foam 66 Fire Service Manual solution should be collected from the foam mak ing equipment 30 seconds after foam production commences T
51. adverse Firefighting Foam Technical 15 Table 7 1 Home Office Recommended Minimum Application Rates of Foam Solution For the Production of Low Expansion Foam For Use on Liquid Hydrocarbon Fuel Class B Fires Foam Type Minimum Application Rate of Foam Solution Ipm m 7 Spill Bund Tanks Tanks Tanks D lt 45m D gt 45m D gt 8lm D lt 8 Im Protein 6 5 NR NR NR Fluoroprotein 5 8 0 9 0 168 AFFF 4 eer o FFFP 4 6 5 ta wb AFFF AR 4 7 6 5 7 ee FFFP AR 4 6 5 Ai Notes to Table 7 1 lt less than lt less than or equal to More than gt more than or equal to gt D Diameter of tank m metre NR Not Recommended for this use Minimum Application Time Minutes Spill Tanks Tanks Fuel Fuel Flashpoint Flashpoint gt 40 C lt 4 C Bund NR NR 45 60 45 60 45 60 45 60 45 60 Ipm m litres per minute of foam solution per square metre of burning area of fire Table 7 2 Home Office Recommended Minimum Application Rates of Foam Solution For the Production of Medium Expansion Foam For Use on Liquid Hydrocarbon Fuel Class B Fires Foam Type Minimum Application Rate of Foam Solution Ipm m 7 Spill Bund SYNDET 6 5 Fluoroprotein 5 0 AFFF 4 0 FFFP 4 0 AFFF AR 4p FFFP AR 40 Notes to Table 7 2 Minimum Application Time Minutes Spill 15 15 Ipm m litres per minute of foam solution per square metre of burning area of fire 76 Fire Service Manual Bund 60 60 60 60 60 60 wea
52. ale Petroleum Fires B P Johnson 1993 ISBN 0 86252 949 2 6 Foundation For Water Research R amp D Note 339 A Review of Fire Fighting Foams to Identify Priorities For EQS Development I CFBAC JCFR Report 49 The Use of Foam Against Large Scale Petroleum Fires Involving Lead Free Petrol Summary Report J A Foster 1992 8 CFBAC JCFR Report 43 Equipment For The Induction Of Additives Into Hose Reel Systems J A Foster B P Johnson 1991 ISBN 0 86252 652 3 9 FRDG Publication 1 94 A Brief Assessment of a Compressed Air Foam System M D Thomas 1994 ISBN 1 85893 149 5 FRDG Publication 3 91 Additives for Hosereel Systems Trials of Foam on Wooden Crib Fires B P Johnson 1991 Firefighting Foam Technical 19 Firefighting Foam Technical Further Reading i CFBAC JCFR Report 40 Survey of Firefighting Foams Associated Equipment and Tactics Ewbank Preece Reports 1990 ISBN 0 82652 556 X Part Firefighting Foams Part 2 Tactics and Equipment Part 3 Large Tank Fires 2 Fire Service Manual Volume 2 Fire Service Operations Petrochemicals 2 Fire Service Manual Volume 2 Fire Service Operations Firefighting Foam 4 CFBAC JCFR Report 46 Additives for Hosereel Systems Summary Report B P Johnson 1992 5 CFBAC JCFR Report 48 An Assessment of the Damage to Tank Farms in Kuwait Following Hostilities and their Implications for UK Practice Summary Report M W Freeman
53. am solution drains out of finished foam and hence provides an indication of the stability of the foam blanket Drainage time is often used to compare the quality of various finished foams however it does not provide a reliable indication of the firefighting capability of foams A long drainage time and hence slow loss of water from the finished foam tends to indicate that the finished foam is capable of maintaining its stabili ty and heat resistance This is usually the case with most P FP AFFF AR and FFFP AR foams However this 1s not true for low expansion SYN DET foams which generally produce finished foams with long drainage times but have very poor heat resistance A short drainage time tends to indicate that the fin ished foam loses its water content quickly and ren ders it vulnerable to high temperature flame and hot surfaces AFFFs and FFFPs tend to have low drainage times and poor heat resistance The drainage times of finished foams depends not only on the foam concentrate but also on the foam making equipment used to produce it Secondary aspirated equipment will produce finished foams with short drainage times while primary aspirated equipment will generally produce finished foams with significantly longer times In addition in pri mary aspirated equipment the more working that takes place the longer the drainage times Drainage for low expansion foams is usually expressed as 25 drainage time This 1s defined
54. ame Firefighting Foam Technical J The performance of firefighting foams can be greatly influenced by The type of foam making equipment used and the way it is operated and main tained The type of foam concentrate used The type of fire and the fuel involved The tactics of foam application The rate at which the foam is applied The quality of the water used The length of pre burn The most effective and efficient use of firefighting foam can only be achieved after full consideration has been given to all of the above factors This Volume of the Manual describes all aspects of firefighting foam and discusses the types of equip ment typically used by the fire service to produce it Topics covered include the properties of foam concentrates finished foams and foam equipment application rates and the classes of and types of fire for which foam can be used Volume 2 of the Manual describes the operational use of foam including recommended minimum application rates and application techniques practical scenario considerations and the logis tics involved in dealing with fires in storage tanks At the rear of this Volume there is a glossary of terms used in this Manual and other terms that may be used in connection with firefighting foams It must be stressed that this Manual only gives general information on the use of firefighting foams Incidents requiring the use of foam are varied and preplanning in
55. ams 5 1 5 3 Foam Concentrates 5 1 5 4 Typical Uses and Properties of Low Medium and High Expansion Finished Foams 6 Chapter 2 Foam Concentrates tJ 2 1 Types of Foam Concentrate 7 2 1 1 General 7 2 1 2 Protein Based Foam Concentrates 8 a Protein P 8 b Fluoroprotein FP 9 c Film forming Fluoroprotein FFFP 9 2 1 3 Synthetic Based Foam Concentrates 9 O a Synthetic Detergent SYNDET 9 b Aqueous Film forming Foam AFFF 9 2 1 4 Alcohol Resistant Foam Concentrates AFFF AR and FFFP AR 10 2 1 5 Hazmat Foam Concentrates 11 2 1 6 Wetting Agents 11 2 1 7 Class A Foam Concentrates 12 2 1 8 Fuel Emulsifiers 12 22 Handling and Storage of Foam Concentrates 12 2 2 1 Compatibility 12 2 2 2 Viscosity 13 2 2 3 Corrosion 14 2 2 4 Storage and Use Temperature Conditions 14 2 2 5 Order of Use 15 2 2 6 Storage Containers and Bulk Storage 15 Firefighting Foam Technical V Chapter 3 Foam Concentrate Standards and Periodic Testing 3 1 3 2 32l 3 2 2 3 2 3 3 2 4 aa 3 2 6 32 7 3 2 8 33 Sal 3 3 2 SI 3 3 4 J39 3 3 6 3 3 7 3 3 8 3 3 9 3 3 10 3 4 3 4 1 3 4 2 3 4 3 3 4 4 General Physical Property Tests of Foam Concentrates General Specific Gravity Relative Density pH acidity alkalinity Sediment Sludge Spreading Coefficient Effects of Freeze Thaw Accelerated Ageing Viscosity Foam Concentrate Standard Fire Tests General Is the Fuel Commonly Encountered Operationally Is the Fuel Reproducibl
56. and fire engulfment hazards Boil over Violent ejection of flammable liquid from its container caused by vaporisation of a water layer beneath the body of the liquid It will generally only occur after a lengthy burning period in wide flashpoint range products such as crude oil The water layer may already have been in the container before the fire began or may be the result of the inadvertent application of water perhaps dur ing cooling of the container walls or from the drainage of foam solution from finished foam applied to the fire see also froth over and slop over Bund area Dike area An area surrounding a storage tank which is designed to contain the liquid product in the event of a tank rupture Branch A hand held foam maker and nozzle Burnback resistance The ability of a foam blanket to resist direct flame and heat impingement Candling Refers to the thin intermittent flames that can move over the surface of a foam blanket even after the main liquid fuel fire has been extinguished Chemical foam A finished foam produced by mixing two or more chemicals The bubbles are typically caused by carbon dioxide released by the reaction Classes of Fire In the UK the standard classification of fire types is defined in BS EN 2 1992 as follows Class A fires involving solid materials usually of an organic nature in which combustion normally takes place with the formation of glowing embers Class B fires
57. and security against reignition however use of water spray can be perfectly satisfactory and far less expensive in many cases The primary mechanisms by which foams extin guish high flash point liquid fires is by cooling the liquid surface and cutting out back radiation from the flames The smothering action of foam plays a relatively insignificant role c Low Flash Point Water immiscible Class B Liquids Water immiscible liquids with low flash points or class A and B petroleum liquids have flash points below 21 C and 55 C respectively These include class A petroleum liquids such as aviation gaso line benzene crude oil hexane toluene and petrol including lead free and class B petroleum liq uids such as avtur jet fuel and white spirit Spills or pools of low flash point liquids can pro duce flammable vapour under normal ambient temperatures and flammable or explosive concen trations can accumulate at low level since most of the vapour will be heavier than air Water sprays are unsuccessful in extinguishing fires in low flash point liquids because vapour gen eration is not sufficiently reduced by the degree of cooling achieved However considerable reduc tions in flame height and radiation intensity can be achieved with water spray application Obviously care should be taken to ensure that the fuel does not overflow any containment In addition where the fuel is not contained the application of water will r
58. antity of vapour produced is too small to sustain burning In addi tion water is generally much denser than liquid hydrocarbons consequently when applied during firefighting it immediately sinks below their sur faces without having any beneficial effect in fire fighting terms on the fire In fact the application of water may cause the surface area of the fire to increase and spread to previously unaffected areas Foam is generally applied to both high and low flash point hydrocarbon fuel fires because it pro vides a visible blanket which controls and extin guishes these fires faster and more effectively than water The three categories of Class B liquids and their firefighting characteristics are described in the fol lowing Sections a DA b High Flash Point Water immiscible Class B Liquids Water immiscible liquids with high flash points or class C petroleum liquids are those with a flash point above 55 C such as gas oils some diesel oils heavy fuel oils and heavy lubricating oils At nor mal ambient temperatures these liquids have low vapour pressures and so do not generate flamma ble concentrations of vapour Water spray can be used to extinguish fires in high flash point liquids since the cooling effect of water is sufficient to reduce the generation of vapour to below the concentration needed to sustain com bustion Firefighting foams are very effective against this type of fire giving very rapid control
59. applications of film forming foams see Chapter 3 Section 3 2 5 Film formation is a very controversial area of fire fighting foams Some firefighters insist that fires can be seen to be controlled and extinguished well ahead of any foam blanket formed others say that they have seen no evidence of the effects of film formation Aqueous films offer little or no burnback protec tion and in any case it can be impossible for fire fighters to see where the transparent surface film remains intact and where it has been broken The manufacturers of film forming foam concen trates often state that they may be used primary aspirated secondary aspirated or non aspirated for application against hydrocarbon liquid fuel fires Petrol fire tests carried out using UK fire service equipment and tactics Reference 3 found that pri mary aspirated film forming foams extinguished the fires in half of the time taken by the same foams used secondary aspirated Also the burn back performances of the primary aspirated foams were vastly superior to those of the secondary aspirated foams The thinness of the film and the uncertainty of its formation makes film forming foams unsuitable for vapour suppression unless a thick foam blanket is also present For vapour suppression primary aspirating equipment will provide a better protec tive foam blanket than secondary or non aspirating equipment Some foam manufacturers say adequate vapour sup
60. are must be taken with the non freeze protected versions as some of these should not be subjected to freezing and their minimum use temperature is often around 2 C As mentioned previously see Section 2 2 2 above foam concentrates generally become more viscous the cooler they become Consequently the minimum use temperature given by manufacturers for their foam concentrates is often based on their assessment of how the viscosity of their products will affect the induction rate When used at or near their minimum use temperature the viscosity of some foam concentrates will be so great that they will not be picked up at the correct rate by some foam induction equipment Manufacturers recommend minimum and maxi mum storage temperatures for their foam concen trates This can be a very wide temperature range for instance some freeze protected foam concen trates can be stored at between 29 C and 60 C Care should be taken to ensure that foam concen trates are not subjected to temperatures outside of the ranges specified by the manufacturers Should this occur especially over long periods of time then it is likely to seriously impair the firefighting performance of the foam concentrates It should be noted that some foam concentrates have recommended maximum storage tempera tures of 40 C It is quite possible for temperatures of this order to be regularly reached in storage con tainers kept in direct sunlight
61. as aa the time taken for 25 of the original foam solu tion content by volume to drain from the finished foam For medium and high expansion foams 50 drainage times are normally given Figure 4 1 shows the basic principles of measuring low expansion foam expansion ratios and drainage times The current British Standards for foam con centrates see Chapter 3 should be referred to for exact details of equipment and test methods to be used Expansion ratios and drainage times of fin ished foams can only be reliably compared if the same type of foam concentrate measuring equip ment foam making equipment and measurement methods are used In particular the height of the measurement container has a significant impact on the length of drainage time measurements short containers give short drainage times tall contain ers give longer drainage times Firefighters should remember that when a foam drains its volume will seem almost unchanged Although its integrity may appear good its fire resistance will be low as it will have lost much of its foam solution content 4 8 Vapour Suppression It is extremely important that foam blankets pre vent fuel vapour percolating through to their upper surface If the foam blanket is unable to prevent this then it is likely that the vapour will continue to burn on the surface of the foam This can quick ly lead to the complete destruction of the foam blanket 4 9 Burnback Resistance
62. ble for its purpose Although the physical property tests discussed above will indicate possible changes in the consis tency of the foam concentrates it 1s the firefight ing performance that is of most interest If the physical property tests indicate a problem then a fire test should be considered in order to investi gate the effects of this on the firefighting perfor mance of the foam concentrate The fire tests performed by manufacturers and test houses on a routine basis are generally based on or around methods and equipment specified in foam concentrate standards Typical of this is the 0 25m area tray fire test specified within the UK Ministry of Defence MoD foam concentrate standards DE see this Chapter Section 3 1 This size of fire test is also recommended for quality control use during foam concentrate production in the British European and International standards for firefight ing foam concentrates see this Chapter Section 3 1 However the main difference is that the MoD tests involves the use of avgas or avtur as fuel and the British European and International standards use heptane see this Chapter Section 3 3 for information on test fuels In order to make the best use of fire test information it 1s necessary to have previous fire test data available so that true comparisons can be made For instance if batch fire test data was available for the foam concen trate when originally purchased then as lon
63. brigades have developed pressurised foam concen trate supply systems in which the foam concentrate is pumped from bulk storage containers directly to the delivery equipment This is often achieved by utilising the pumping units on foam tenders to con vey the foam concentrate to the induction device which may take the form of an in line inductor or a constant flow valve Brigades have their different versions of this sys tem but they will all usually include some type of distribution manifold and metering device 58 Fire Service Manual Figure 5 20 Diagram showing one 900 litre min and two 450 litre min foam branchpipes receiving a pressurised foam concentrate supply from a foam tanker or foam main Pressurised foam concentrate supply from bulk foam source When pumping foam concentrate to in line induc tors in particular care should be taken to ensure that the system has been correctly designed for this situation This is mainly because these inductors are calibrated for their normal operating mode where they create their own small partial vacuum in order to suck up foam concentrate see this Chapter Section 5 3 2 However when foam concentrate is pumped under pressure directly to them this will act in addition to the partial vacuum and will result in foam concentrate being intro duced into the system at a much higher concentra tion than required Three other methods of feeding foam concentrate under p
64. ce area per minute Ipm m AFFF concentrate Aqueous film forming foam AFFFs are generally based on mix tures of hydrocarbon and fluorinated surface active agents and have the ability to form an aqueous film on the surface of some hydrocarbon fuels Aspiration The addition or entrainment of air into foam solution Aspirated foam Foam that is made when foam solution is passed through purpose designed foam making equipment such as a foam making branch These mix in air aspirate and then agitate the mixture sufficiently to produce finished foam see also primary aspirated foam and secondary aspirated foam Base injection The introduction of fuel tolerant primary aspirated finished foam Subsurface injection beneath the surface of certain flammable and combustible hydrocarbons to effect fire extinguishment Usually used for the protection of fixed roof hydrocarbon fuel storage tanks Bite The formation of an initial area of foam blanket on the surface of a burning liquid fuel Firefighting Foam Technical 8 Boiling liquid The catastrophic failure of a tank containing pressure liquefied expanding vapour gas PLG due to mechanical damage or adverse heat exposure explosion BLEVE will result ina BLEVE A BLEVE will produce blast and projectile hazards If the contents of the tank are toxic then health and exposure hazards may occur If the contents are flammable then a fireball may occur with associated thermal radiation
65. cked up As a result when using these viscous foam concentrates foam induction sys tems may need to be re calibrated In addition as the temperature of the alcohol resistant foam con centrates falls towards freezing 0 C the rate at which they are picked up by the induction system will reduce further due to increasing viscosity possibly even making the re calibration inaccu rate Alcohol resistant foam concentrates are primarily designed for the production of low expansion foams although they may also be used to produce medium expansion foams for application to hydro carbon and water miscible liquids Versions are available for use with sea and fresh water For AFFF AR the suggested materials for bulk storage containers and equipment are the same as AFFF that is stainless steel GRP epoxy lined car bon steel and polyethylene For FFFP AR as with P FP and FFFP foam con centrates it is suggested that bulk storage contain ers should ideally be constructed from materials such as epoxy coated carbon steel GRP or poly ethylene Alcohol resistant versions of P FP and SYNDET foam concentrates are available although they are uncommon in the UK They are used in other European countries in particular FP AR is widely used in France 2 1 5 Hazmat Foam Concentrates Many materials used in industrial and chemical processes release toxic odorous and or flammable vapour when in contact with the atmosphere If a spill occur
66. concentrates of a particular type of manufacturer s foam should be virtually identical The lower the percentage concentration the less foam concentrate that is required to make fin ished foam The use of say 3 foam concentrate instead of 6 foam concentrate can result in a halving of the amount of storage space required for the foam concentrate with similar reductions in weight and transportation costs while main taining the same firefighting capability Not all foam concentrates are available in the highly con centrated form e g alcohol resistant and pro tein based foam concentrates This 1s because there are technical limits to the maximum usage concentrations of some of the constituents of foam concentrates It is extremely important that the foam induction equipment used is set to the correct percentage If 3 concentrate 1s induced by an induction system set for 6 concentrate then twice the correct amount of foam concentrate will be used creating a foam solution rich in foam concentrate Not only will this result in the foam supply being depleted very quickly and an expensive waste of foam con centrate but it will also lead to finished foam with less than optimum firefighting performance mainly due to the foam being too stiff to flow ade quately Alternatively using 3 foam concentrate where the system is set for 1 will result in a solu tion with too little concentrate to make foam with adequate firefighting perfor
67. cooling to continue Alcohol resistant foam concentrates lose effectiveness unless they are applied gently to the surface of polar liquids avoiding plunging 6 1 3 Class C Fires Class C fires are those involving gases or liquefied gases In recent years liquefied flammable gases have become an increasingly important source of fuel in commerce and industry Increased use brings increased transportation of these liquids through out the country by road rail and in UK coastal waters which in turn increases the possibility of accidental spillage The product group includes LPG Liquefied Petroleum Gas usually propane or butane liquid ethylene and LNG Liquefied Natural Gas i e methane Boiling points for these liquefied gases are low and so in the event of spillage rapid vapour pro duction occurs Due to the greater amounts of vapour produced and the low buoyancy of cold vapour the dispersal of this vapour is more prob lematical than from spilled flammable liquids such as petrol In still air conditions and where the ground is sloped or channelled this vapour can travel long distances from its source Liquefied gas vapour has been known to travel 1 500 metres T2 Fire Service Manual from a spilled pool of liquid whilst retaining a con centration above the lower flammability limit Medium and high expansion foams are suitable for liquefied gas spills both for fire extinguishment and vapour suppression The surface of the
68. e How Long is the Preburn How Deep is the Fuel What is the Application Rate How is the Foam Applied Under What Conditions are the Fire Tests Performed What Burnback Test is Used When are the Fire Tests Carried Out Periodic Testing of Foam Concentrates General Collection of Foam Concentrate Samples Typical Physical Property Tests a Specific Gravity Relative Density b pH Acidity Alkalinity c Sediment Sludge d Spreading Coefficient Periodic Fire Tests Chapter 4 The Properties of Finished Foams and The Effects 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 4 10 4 11 4 12 4 13 4 13 1 4 13 2 vi of These on Firefighting Performance General Working Foam Flow Fluidity Film Formation Fuel Tolerance Edge Sealing Foam Blanket Stability Drainage Time Vapour Suppression Burnback Resistance Water miscible Fuel Compatibility Suitability For Subsurface Base Injection Quality of Finished Foam Compatibility of Finished Foams With Other Finished Foams With Dry Powder Fire Service Manual 17 17 19 19 19 19 19 19 20 20 20 20 20 20 21 21 21 21 21 22 22 22 22 22 23 24 24 24 24 24 24 2l 27 28 28 29 30 30 31 31 32 32 32 33 33 33 4 14 4 14 1 4 14 2 4 15 4 15 1 4 15 2 4 15 3 Typical Characteristics of Finished Foams General Individual Foam Characteristics a P b FP c FFFP d Synthetic SYNDET e AFFF Alcohol Resista
69. e of a round the pump proportioner system where there ts a built in foam tank To Suction inlet Oe 6 9 HQ Dial Foam x Required setting equipment percentage flow rate concentration 100 193 x 3 100 Dial 5 8 Ipm setting However each time the flow to the foam making equipment changes then a new setting would have to be calculated to maintain accurate foam concen tration Round the pump systems require the pressure on the suction side of the pump to be less than one third of the pressure on the delivery side in order to function correctly If this is not the case then water may be forced into the foam concentrate Figure 5 18 A typical round the pump proportioner Top cutaway view Bottom external view Flow level a indicator Drive pin ee f an si Nt Rotating grip handle container Pressure contro valves are available which can help to reduce this problem see below Another drawback of this type of equipment is that the foam solution has to pass through the pump casing This may cause corrosion problems within the pump and other areas of the appliance where the foam solution may enter such as the water tank and pipework In addition the orifices within the inductor are extremely small these can easily be blocked by small pieces of debris or foam concen trate sludge Once blocked the system must be taken apart and the debris removed For
70. e additional problems for firefight ers These quickly attack finished foams by extracting the water they contain This rapidly leads to the complete destruction of the foam blanket Consequently special firefighting foams generally known as alcohol resistant foam con centrates have been developed to deal with these particular types of liquid Some firefighting foams have also been developed specifically for use against class A fires The main properties of firefighting foams include Expansion the amount of finished foam produced from a foam solution when it is passed through foam making equipment O Stability the ability of the finished foam to retain its liquid content and to maintain the number size and shape of its bubbles In other words its ability to remain intact Fluidity the ability of the finished foam to be projected on to and to flow across the liquid to be extinguished and or protected Contamination resistance the ability of the finished foam to resist contamination by the liquid to which it 1s applied Sealing and resealing the ability of the foam blanket to reseal should breaks occur and its ability to seal against hot and irregu lar shaped objects Knockdown and extinction the ability of the finished foam to control and extinguish fires Burn back resistance the ability of the fin ished foam once formed on the fuel to stay intact when subjected to heat and or fl
71. e fire service for this purpose are in line inductors round the pump proportioners Whatever foam induction or injection equipment 1s used its operation should be checked regularly to ensure that the rate at which the foam concentrate is introduced into the water stream 1s accurate Such checks should involve the whole of the foam system to be used operationally including the foam making equipment the foam concentrate typical hose runs and typical pump branch operat ing pressures and flows to ensure that the system as a whole works as expected Problems that may occur include long hose runs producing high back pressures which prevent the induction equipment proportioning correctly or at all foam concentrates that are too viscous to be picked up at the correct rate by the induction equipment Different types and manufacturers versions of foam concentrates will be of different viscosity These will affect the accuracy of the induction equipment blocked or obstructed orifices within the induction equipment poorly calibrated induction equipment Note the calibration of new induction equipment should always be checked with the foam making equipment and foam con centrates it 1s to be used with incorrect inductor for the foam making equipment being used or for the required concentration of foam concentrate Note some manufacturers colour code their induction and foam making equipment to assist
72. e in the USA for more than 20 years in fighting wildland fires but more recently they have been gaining in acceptance there for use in structural firefighting Class A foam concentrates are often synthetic detergent foam concentrates that have been for mulated for use on class A fires only They are claimed to reduce the surface tension of water to increase its capacity to spread and penetrate class A fuels Consequently if this is the case some class A foams may also be defined as wetting agents see above Generally they are formulat ed for use at concentrations of up to 1 They are mostly intended for use either non aspirated or secondary aspirated using standard water branches Some have also found use in com pressed air foam systems CAFS see Chapter 5 Section 5 4 Tests carried out in the UK Reference 4 have shown that class A foams and the two convention al foams tested i e AFFF and SYNDET perform l 2 Fire Service Manual no better than water when used to extinguish fires in wooden pallets 2 1 8 Fuel Emulsifiers Fuel emulsifiers are mixtures of emulsifiers wet ting agents and other additives They are generally designed for use at concentrations between 0 5 and 6 in water and may or may not produce foams They are formulated specifically for appli cation to class B petroleum based fuels although some manufacturers also recommend their use for class A fires Fuel emulsifiers are oleophilic in ot
73. e rapid depletion of oxygen from water due to high biodegradability This has the effect of asphyxiat ing aquatic organisms They concluded that slow er low biodegradability of foam concentrates may in fact be more desirable when making future environmental hazard assessments They also found that manufacturers only provide limited biodegradability test data which was of lit tle use in differentiating between the biodegrad ability of different foam concentrates From the data available there were indications that foam type was not a good indicator of biodegradation potential Five different foam types were of low biodegradability these were SYNDET P FP AFFF and AFFF AR However some AFFF and SYNDET foam concentrates were of high biodegradability None of the data gathered enabled an assessment to be made of the biodegradability of the fluoro surfactants contained in AFFF AFFF AR FP FFFP and FFFP AR foam concentrates These chemicals may remain persist in the environment for long periods of time before degrading 0 0 D 9 Firefighting Foam Technical Chapter Chapter 5 Equipment 5 1 General This Chapter describes some of the foam equip ment that 1s currently in use within the UK fire ser vice The aim is not to describe every item of equipment available but to give examples and indi cations of their performance The two main types of foam equipment described here ate Foam making equipmen
74. eleased from the foam as it breaks down The use of medium expansion foam against indoor class A fires such as in warehouses could be a more effective and efficient use of foam It should be possible to restrict the foam application so that the area of origin of the fire is kept under observa tion whilst maintaining sufficient foam flow to force the foam onto the fire 70 Fire Service Manual 6 1 2 Class B Fires a General Class B fires are those which involve flammable liquids liquefiable solids oils greases tars oil based paints and lacquers i e flammable and combustible liquids Combustion of these occurs entirely in the vapour that is present above the sur face of the liquid For firefighting purposes Class B liquids can be subdivided into three categories each requiring different properties from firefight ing foams in order to achieve effective and effi cient fire control and extinction The categories are high flash point water immiscible Class B liquids low flash point water immiscible Class B liquids water miscible Class B liquids Some high flash point liquid hydrocarbon fires such as those involving fuel oils can under very controlled conditions be extinguished using only the cooling effect of water However most low flash point hydrocarbon fires such as those involving petrol cannot be extin guished by water alone as the fuel cannot be low ered to a temperature where the qu
75. ensure that the finished foam is of optimum quality The more concentrated a foam concentrate e g a l foam concentrate is more concentrated than a 3 foam concentrate the lower the rate of flow that the foam concentrate is required to be intro duced in to the water stream Consequently espe cially for 1 systems even slight variations in the foam concentrate flow can result in much weak er stronger foam solutions being produced than required If too little foam concentrate is picked Pelton wheel Cm 8 4 6 6 8 ete Las 50 Fire Service Manual up a weak foam solution will be formed which is likely to produce a poor blanket of quickly drain ing foam If too much foam concentrate is picked up a strong foam solution will be formed which is likely to produce foam that is too stiff to flow ade quately across the surface of a fuel probably result ing in poor firefighting performance In addition expensive foam concentrate will be wasted and the possible overall duration of firefighting will be reduced due to rapid consumption of the available supply of foam concentrate Typically variations in the accuracy of induc tion injection equipment of or 10 of the required concentration are usually acceptable and are unlikely to affect firefighting performance that 1S for 1 concentrate induction rate to be between 0 9 and 1 1 for 3 concentrate induction rate to be between 2 7 and 3 3 for 6 co
76. ery poor resistance to fuel contamination often resulting in poor extinction and burnback performance Medium and high expansion applications of SYNDET are relatively gentle and so fuel contamination is less of a problem very poor sealing around hot objects often resulting in poor extinction performances poor burnback resistance poor vapour suppression capabilities at low expansion vapour suppression characteristics much improved at medium and high expansion unsuitable for use with polar fuels unsuitable for subsurface base injection e AFFF Low expansion AFFF finished foams tend to have the following useful characteristics usable foam can be produced with minimal working manufacturers suggest that they can be used primary and secondary aspirat ed flow quicker than P and FP foams over liq uid fuel surfaces quickly reseal breaks in 36 Fire Service Manual the foam blanket and flow around obstruc tions This often results in very quick fire knockdown and extinction On some liquid hydrocarbon fuels these characteristics may be enhanced by the film forming capabilities of AFFF suitable for subsurface base injection moderate resistance to fuel contamination although not as fuel tolerant on non water miscible fuels as alcohol resistant foams or FP foams and the following disadvantages poor at sealing against hot objects poor foam blanket stability and very quick foam drai
77. es Medium expansion foam making branches are generally designed to be used with SYNDET foam concentrates although other types such as FP AFFF AFFF AR FFFP and FFFP AR may also be used MX foam making branches will produce foam at expansions usually ranging from 25 1 to 150 1 As a result of these higher expansion ratios Firefighting Foam Technical 45 thee ee ee Figure 5 8 A medium expansion hand held foam making branch Photo Mid and West Wales Fire Service the projection distances of MX foam are much less than for LX foam If at all possible before pur chase or operational use this type of equipment should be operated to ensure that acceptable throws are achieved With MX foam making branches an in line inductor is generally used to introduce the foam concentrate as a premix The branch then diffuses and aerates the stream of foam solution and pro jects it through a gauze mesh to produce bubbles of a uniform size MX hand held branches in use typically have nominal flow requirements ranging from 225 lpm to 450 lpm with inlet pressures ranging between 1 5 bar and 8 bar The expansion ratio of the foam produced is usually claimed by the manufacturers to be in the region of 65 1 with throws ranging from 3 to 12 metres Typical foam output is claimed to be approximately 13 m min for 225 lpm branches and approximately 26 m min for 450 lpm branches 46 Fire Service Manual 5 2 7 LX and MX Hand held Water B
78. es for such applications They claim that the finished foam produced usually has an expansion ratio of less than 4 1 Firefighting Foam Technical Chapter Chapter 2 Foam Concentrates 2 1 Types of Foam Concentrate 2 1 1 General There are a number of different types of foam con centrate available Each type normally falls into one of the two main foam concentrate groups that is to say they are either protein based or synthetic based depending on the chemicals used to pro duce them Protein based foam concentrates include Protein P Fluoroprotein FP Film forming fluoroprotein FFFP Alcohol resistant FFFP FFFP AR Synthetic based foam concentrates include Synthetic detergent SYNDET Aqueous film forming foam AFFF Alcohol resistant AFFF AFFF AR The characteristics of each of these foam concen trates and the finished foams produced from them varies As a result each of them has particular properties that makes them suitable for some applications and unsuitable for others For protein based foam concentrates the basic chemical constituent is hydrolysed protein obtained from natural animal or vegetable sources It is the hydrolysed protein the foaming agent that enables bubbles to be produced For synthetic based foam concentrates the basic constituents are detergent based foaming agents To enhance the firefighting properties of these basic constituents and hence produce the differe
79. ests to be carried out once at the approval stage Conformance with the standards is then only checked via physical property tests probably by the manufacturer 3 4 Periodic Testing of Foam Concentrates 3 4 1 General Storing foam concentrates as recommended by the manufacturers and as described in Chapter 2 Section 2 2 will help to maintain them in a usable condition However no matter how well they are stored deterioration will take place Consequently it is important that samples of stored foam concen trates are tested periodically e g annually to ensure that they have not significantly deteriorated and that they remain able to effectively extinguish fires There are a number of ways of having periodic testing carried out these include Carry out testing at brigade level Return a sample to the supplier Send a sample to an independent laboratory The range of tests that shouid be carried out to evaluate the condition of foam concentrates requires some specialised equipment and technical expertise It would not be cost effective or practi cal for individual brigades to carry out the few tests that would be required each year Most foam concentrate manufacturers will carry out this type of testing for a fee However some organisations consider it undesirable to rely on manufacturers tests when the manufacturer has a clear commercial interest in the outcome Whilst there is no suggestion that any supplie
80. esult in further fuel spread Firefighting foams are effective on low flash point liquids because they trap the vapour at or just above the liquid surface The trapped vapour then sets up an equilibrium with the liquid which pre vents further vapour generation Where deep foam blankets can be formed such as in storage tanks with a large freeboard this process may be assist ed by the increased pressure exerted by the heavier blanket Film forming foams produce a thin film on the surface of some of these class B liquids which may also prevent vapour escaping Additional benefits of using firefighting foams on these liquids are that they cool the liquid surface reduce the vapour generation rate obstruct radia tion from the flame to the liquid surface and reduce the oxygen level by the production of steam where the foam flame and liquid surface meet Lead as lead tetra ethyl or lead tetra methyl has been used for more than 60 years to improve the performance octane rating of the hydrocarbon mixtures that constitute petrol However since 1974 health and environmental concerns have resulted in the progressive reduction in the amounts of lead in petrol This reduction of the lead content has led to the use of oxygenates for example ethers and alcohols as alternative octane improvers Oxygenates are only used in either leaded or lead free fuels when the octane rating cannot be achieved cost effectively by refinery processes
81. expansion applications SYNDET foam concentrates are usually manufac tured for use at between 1 and 3 concentra tions and versions are available for use with sea and fresh water They are of similar cost to P and FP foam concentrates Manufacturers have indicated that SYNDET foam concentrates are not particularly corrosive However testing Reference 2 and reports received from brigades indicate that adverse corro sion and degradation effects can occur with mate rials such as epoxy coated carbon steel GRP and aluminium Materials that should be considered for bulk storage containers and equipment for both concentrate and solution are 316 stainless steel or polyethylene b Aqueous Film forming Foam AFFF AFFF foam concentrates are solutions of fluoro carbon surface active agents and synthetic foaming Firefighting Foam Technical 9 agents Under certain conditions this combination of chemicals can as well as producing a foam blanket allow a very thin vapour sealing film of foam solution to spread over the surface of some liquid hydrocarbons AFFF foam concentrates are usually available for use at 1 3 or 6 concentrations and versions are available for use with fresh and sea water They are primarily intended for the production of low expansion foams although they can also be used to produce medium expansion foams Due to their film forming properties they can be applied sec ondary aspirated and can be used to
82. fire It will consist of a mixture of foam solution that has been mixed with air The foam may be primary aspirated or secondary aspirated Any liquid having a flashpoint below 37 8 C 100 F The re ignition of a flammable liquid caused by the exposure of its vapour to a source of ignition such as a hot metal surface or a spark The lowest temperature at which a flame can propagate in the vapour above a liquid The nominal supply rate of foam solution required by a foam branch measured in litres per minute A hydrolysed protein based foam concentrate with added fluorinated surface active agents The result of mixing foam concentrates water and air to produce bubbles The foam as supplied by the manufacturer in liquid form this is sometimes referred to as foam compound foam liquid or by trade or brand names Foam with a long drainage time 1 e the liquid content of the foam takes a long period of time to drain out of the foam the foam 1s very stable A mechanical device in which foam solution is sprayed onto a net screen through which air is being forced by a fan Similar to a foam making branch but inserted in a line of hose so that the finished foam passes along the hose to a discharge nozzle The equipment by which the foam solution is normally mixed with air and delivered to the fire as a finished foam A larger version of a foam making branch which cannot be hand held A well mixed solution of f
83. foam concentrates basically consist of protein foam concentrates with the addition of fluorinated surface active agents fluorosurfactants The addi tion of fluorosurfactants provides oleophobic oil repellent properties and makes the finished foam more fluid This greatly improves the fire knock down performance of the finished foam when compared to that of protein foam Other additives can include solvent sodium chloride iron magne sium and zinc FP foam concentrates are usually available for use at 3 or 6 concentrations and versions are avail able for use with sea and fresh water They are only marginally more expensive than protein foam concentrates FP foam concentrates are primarily intended for the production of low expansion foams although they have also proved effective when used to pro duce medium expansion foam They are not rec ommended for the production of high expansion foam Uses are widespread in the fire service the petro chemical industry and armed forces throughout the world As with protein foam concentrates corro sion inhibitors are not often included However consideration should be given to constructing bulk storage containers from materials such as epoxy coated carbon steel GRP or polyethylene c Film forming Fluoroprotein FFFP FFFP foam concentrates are based on FP foam concentrates with the addition of film forming flu orinated surface active agents Under certain con ditions this c
84. foam making eguipment This equipment produces foam by spraying the foam solution on to a mesh screen or net Air is then blown through the net or mesh either by entrainment caused by the spray nozzle or by an hydraulic electric or petrol motor driven fan 1 5 3 Foam Concentrates The amount that a foam solution can be aspirated not only depends on the equipment but also on the foam concentrate that is used For instance syn thetic detergent SYNDET foam concentrates are the only type that can be used to produce low medium and high expansion foams protein foam concentrates can only be used to produce low expansion foam and the remaining commonly used foam concentrates i e AFFF AFFF AR FP FFFP and FFFP AR see Chapter 2 are mostly intended for use at low expansion although they can also be used to produce medium expansion foam For flammable liquid fuel fires effective sec ondary aspirated foam can only be produced using a film forming foam concentrate Chapters 2 3 and 4 discuss in detail the various types and properties of foam concentrates and fin ished foams Firefighting Foam Technical 5 1 5 4 Typical Uses and Properties of Low Medium and High Expansion Finished Foams The various expansion ratios are typically used for the following applications Primary Aspirated Finished Foams Low expansion Large flammable liquid fires 1 e storage tanks tank bunds Road traffic accidents Flammable liqu
85. for brigades to eval uate any new hosereel induction system that may come on to the market 5 4 Compressed Air Foam Systems CAFS Compressed Air Foam Systems CAFS are designed to produce aspirated finished foams with out the need of a foam making branch CAFS con sist of a water pump a foam concentrate injection pump and an air compressor which combine to produce an aerated foam at the delivery of the pump CAFS can be appliance or trailer mounted and can be supplied with a range of water pumps concentrate injection pumps and different air com pressors depending on the requirements of the user It is claimed by the manufacturers of these systems that they have longer throws than conventional fire service equipment and that they produce better worked foam with expansion ratios adjustable between 7 1 and 30 1 When used with class A foam concentrates it is claimed that the resulting foam will stick to vertical surfaces and remain there for long periods of time This is said to cool and insulate the material and to prevent the spread of fire from radiated heat CAFS may also be used with other types of foam concentrates Tests Reference 9 have shown that a CAFS can throw foam further than conventional UK fire ser vice foam making branches whilst producing a well worked low expansion foam The system also produced a medium expansion foam with FP that was very sticky and could be used to coat vertical surfaces 5 5 Methods
86. form a foam solution Protein foam concentrate contains organic concentrates derived from natural vegetable or animal sources Hydrolysed products of protein provide exceptionally stable and heat resistant properties to foams although they lack fuel tolerance and have slow knock down performance see Specific gravity Finished foams that are produced from foam solutions that are applied other than by purpose designed foam making equipment usually standard water devices See primary aspirated foam The ability of a foam to seal around hot objects and prevent reignition The measurement of the stiffness of a finished foam sample when measured with a foam viscometer Units of measurement are Newtons per square metre n m When some burning liquids such as heavy fuel oils or crude oils become extremely hot any applied water may begin to boil on contact with the fuel the resulting rapid expansion as it converts to steam may cause burning fuel to overflow its containment and the fire to spread see also boil over and froth over The time taken for foam solution to pass from the point where foam concentrate is introduced in to the water stream to when finished foam is produced The specific gravity of a material is a measure of the density of the material in relation to the density of water The specific gravity is calculated as Specific Gravity Density of material Density of water Firefighting Foam Technical 87
87. g as the same fuel test methods and equipment are used when testing the stored foam concentrate the fire test results can be compared for obvious differ ences in performance If original fire test data is not available but the foam concentrate conformed to a particular foam standard when produced then that standard fire test could be carried out to deter mine whether the stored foam concentrate still complies with that standard Firefighting Foam Technical 25 J DE Firefighting Foam Technical Chapter Chapter 4 The Properties of Finished Foams and The Effects of These on Firefighting Performance 4 1 General In Chapter 2 the various types and properties of foam concentrates were discussed This Chapter explains some of the more important properties of finished foams These properties can greatly affect the firefighting performance of finished foams in terms of Flame knockdown the ability of the finished foam to quickly knockdown flames and control the fire Extinction The ability of the finished foam to extinguish the fire Burnback resistance the ability of the finished foam once formed on the fuel to stay intact when subjected to heat and or flame The properties discussed in this Chapter include O Working the effort required in mixing air with the foam solution to produce a usable finished foam Foam flow fluidity the ability of the finished foam to flow
88. ge containers and accurate records of usage are kept If the foam concentrate complies with a particular standard then the limits specified within the stan dard can also be used to determine whether the foam concentrate still complies with the standard As long as the same test methods and equipment are used the results of periodic testing of stored foam concentrates can be compared with the limits set out in the manufacturers data sheets and with the actual performance of the foam concentrate when originally produced Any discrepancies can then be identified and investigated further It should be remembered that foam concentrates are only part of the equipment and resources nec essary to produce effective firefighting foams Consequently the whole foam making system including the induction or injection equipment pumps typical hose lengths procedures etc should all be periodically checked individually and as a whole system to ensure that all are oper ating correctly and ultimately providing finished foam of the required quality Collection of Foam Concentrate Samples 3 4 2 Foam samples sent for analysis must be represen tative of the contents of the container from which they have been taken Samples can be taken as fol lows One sample From the bottom of the container only or from anywhere in the container after thor oughly mixing the contents Two samples One from the top of the container and one fr
89. h but perfectly adequate when used through the longer foam making branch Details of some of the measurements made of the foam produced by these branches are given in Table 5 1 LX foam making branches operating at their rec ommended pressure usually either 5 5 or 7 bar branch pressure with a flow of 225 Ipm are claimed by the manufacturers to give throw dis tances varying from 12 metres coherent rope to 21 metres no internal baffles etc Hand held LX foam making branchpipes are also available with nominal flow requirements of approximately 450 lpm and 900 lpm at 7 bar branch pressure These are claimed to throw finished foam a few metres further than the 225 lpm branches Some foam making branches are specially designed for use with film forming foam concen trates in crash fire situations These branches have 4 Fire Service Manual adjustable jaws at the outlet giving the option of a cohesive jet or a fan like spray They also have an on off trigger mechanism controlling the release of the foam One adjustable jaw type 225 Ipm foam making branch is claimed by the manufacturer to give throws ranging from 7 metres with the jaws closed 1 e spray mode to 13 metres with the jaws open 1 e jet mode when operated at 7 bar 5 2 3 LX Hand held Hosereel Foam Unit This consists of a portable hand held unit similar to an extinguisher see Figure 5 4 which can contain up to 11 litres of foam concentrate An appliance hose
90. he firefighting performance con tents of this table are based on the results of work carried out on petrol spill fires Reference 5 A difference in performance of one grade is not significant due to the tight cut off points in the results used to generate the Good quality foam concentrates may have better characteristics those of bad quality foam concen trates may be considerably worse Obviously other factors such as fuel application technique and the type of equipment used will also greatly affect these characteristics 4 14 2 Individual Foam Characteristics However where there is a difference in performance of two or more grades the difference is significant JJJ Very Good JU Good J Acceptable J Poor J Very poor LX Low Expansion MX Medium Expansion AX High Expansion SA Secondary Aspirated The firefighting performance contents of this table are based a on the results of work carried out by the Home Office FRDG l on petrol spill sites provide acceptable sealing against hot metal surfaces form stable foam blankets with slow foam drainage times good burnback resistance good vapour suppression and the following disadvantages a P can be used to produce low expansion foam only Low expansion finished foams produced from P require to be well worked to make accept foam concentrates tend to have the following use ful characteristics 34 Fire Service Manual able fini
91. hem or any other foams to form aqueous films on water miscible liquids They will however form an aqueous film between the polymeric membrane and the finished foam blanket This may help to quicken the repair of any breaks that may occur in the polymeric layer Alcohol resistant foam concentrates are normally used at 6 concentration for application to fires of water miscible fuels such as most polar sol vents and at 3 concentration on liquid hydro carbon fuel fires However some alcohol resistant foam concentrates have been specifically designed for use at 3 concentration on both water miscible and hydrocarbon fuels The 3 6 concentrates are similar in price to stan dard AFFF and FFFP concentrates whereas the manufacturers tend to charge more for the single 3 concentrates The viscosity see this Chapter Section 2 2 2 of alcohol resistant foam concentrates can vary enor mously some flow relatively easily while it can be difficult to pour others out of their containers In addition they become more viscous with falling temperature Consequently if these foam concen trates are to be used it is important to ensure that existing induction equipment will pick them up at the correct rate when using typical operational equipment and conditions For instance when using the more viscous foam concentrates it is likely that in line inductor dial settings will be incorrect and not as much concentrate as indicated will be pi
92. hence suffer from severe fuel contamination when vigorously Firefighting Foam Technical 29 applied to a fuel This is because the surface ten sion properties of protein foam allows fuel to spread over and within the blanket This can result in burning within the blanket continuing over a long period of time The fuel tolerances of FP and FFFP foams are con siderably better than that of P foams This is due to the addition of fluorocarbon surface active agents which are oleophobic i e they repel oil and have a very low surface tension These properties help to resist the spread of fuel across foam bubbles and hence increases their fuel tolerance In the case of synthetic detergent based foams the hydrocarbon surface active agents that are used in their formulation tend to emulsify oils with water This causes the foam to pick up large quantities of fuel which can readily ignite Fuel tolerance has been improved in the case of AFFFs and AFFF ARs by the additional use of a high proportion of fluorocarbon surface active agents In contrast to the above fuel emulsifiers see Chapter 2 Section 2 1 8 are oleophilic 1 e they attract oil and rely on mixing well with fuel in order to form an emulsion The emulsion is claimed by the manufacturers to consists of fuel molecules encapsulated in water molecules This they say significantly reduces the amount of vapour released by the fuel making the mixture incapable of sustaining
93. hers words they are oil liking Consequently on application to petroleum based fuels it is claimed that the fuel emulsifier solution mixes with the fuel to form an emulsion which consists of fuel molecules encap sulated in water molecules This 1s said by the manufacturers to significantly reduce the amount of vapour released by the fuel making the mixture incapable of sustaining combustion When used against petroleum fuel fires sufficient mixing of the emulsifier with the fuel by very vigorous direct application to the surface of the fuel 1s said to result in rapid knockdown and extinction of the fire In addition it 1s claimed that because an emul sion has been formed and the fuel molecules have been encapsulated re ignition should not occur and that the mixture is then suitable for disposal with no risk of re ignition On class A fires fuel emulsifiers are claimed to simply act as class A foams see above Emulsifiers have only recently been introduced and their performance relative to other foam con centrates and firefighting media has yet to be proven in the UK 2 2 Handling and Storage of Foam Concentrates 2 2 1 Compatibility Different types and makes of foam concentrate are not generally compatible and manufacturers advice and recommendations should be followed Mixing incompatible foam concentrates may cause sludge and sedimentation to form in the concen trates which may lead to blockages in induction
94. higher percentage of water To overcome high back pressure e g when forcing finished foam through long lengths of ducting or up to a height the by pass is opened and some foam solution is thereby diverted to pass through the turbine to waste giving less for foam AS Fire Service Manual Fine mesh screen TLL E EEEE f TUTTLE LLL production This results in a higher expansion ratio with the finished foam containing a lower percentage of water It also slightly increases the water flow to the turbine speeding up the fan and consequently the air flow Because the finished foam cannot be projected it is often fed to the required application point through a large diameter flexible tube or ducting It can however be used without ducting e g placed on the side of a ship s hold or in the door way of an enclosure The larger HX foam generators are rather bulky items of equipment to carry on a first line appli ance so they are usually brought by special vehi cles when required However some lightweight generators have been developed that can fit into a standard appliance locker One typical large water turbine driven HX foam generator weighs 55 kg and ts claimed by the man ufacturer to produce at 7 bar inlet pressure with a nominal flow of 210 lpm and the by pass closed 135 m min of finished foam with an expansion ratio of between 500 and 700 1 At the same inlet pressure but with a nominal flow of 225
95. his may mean the collection of foam in a large clean bucket with the foam solution that drains off being used The refractive index of the collected foam solution should then be measured using the refractometer and its concentration read off from the calibration graph Different foam concentrate types produce foam solutions with different refractive indices and refractometers only cover limited ranges of refrac tive index Consequently care must be taken to choose the correct refractometer to cover the expected range of the refractive indices of the foam solutions to be tested 5 5 3 Flow Method Another method of checking the induction rate is to use a wide top container for the foam concen trate such as a bucket with calibrated marks per haps every five litres The amount signified by each mark will depend on the rate of foam con centrate pick up expected from the induction equipment and the size of the container Ideally the container should contain the foam concentrate that will be used operationally with the foam equipment Once the foam equipment has been run up to the required operating conditions the pick up tube should be inserted into the container The time taken for the level of the concentrate to fall by for instance 5 10 or 15 litres should then be measured The induction rate can be calculated as follows Flow rate of foam concentrate lpm Amount of foam concentrate used litres x 60 Time taken to use
96. id spill fires Vapour suppression Helidecks Jetties Aircraft crash rescue Portable fire extinguishers Medium expansion Vapour suppression Flammable liquid storage tank bunds Small cable ducts Smal fires involving flammable liquids such as those following road traffic accidents Transformer protection High expansion Knockdown and extinction in and protection of large volumes such as warehouses aircraft hangars cellars ships holds mine shafts etc Large cable ducts Vapour suppression including cryogenic liquids such as LNG LPG Secondary Aspirated Finished Foams Large flammable liquid fires i e storage tanks tank bunds Helidecks Aircraft crash rescue Portable fire extinguishers Low expansion finished foams can be projected over reasonably long distances and heights making them suitable in many situations for use against fires in large storage tanks 6 Fire Service Manual Medium expansion finished foam can only be projected over small distances However with expansions of between 20 and 200 large quantities of foam are produced from relatively small quantities of foam solution This combined with its ability to flow relatively easily makes medium expansion foam ideal for covering large areas quickly High expansion finished foam flows directly out of the foam making equipment and is not project ed any appreciable distance Its coverage of large areas can also be slow but the immense quantity of
97. impact of this run off Firefighting foams can also be of benefit by pre venting the release of flammable or toxic vapour into the environment The use of foams for firefighting is infrequent and at changing locations Consequently the impact on the environment in these areas does not accumu late although it can be severe at the time of the incident In contrast areas used for training are likely to be frequently exposed to contamination by foams and the run off from these sites should be controlled by containment and disposal to appro priate treatment works Generally the environmental effects of foams are considered in terms of their toxicity and their biodegradability It should be remembered that it is the total volume of the foam concentrate that is released into the environment that is of concern it does not matter by how much it has been diluted 4 15 2 Toxicity The aquatic toxicity of a substance i e how poi sonous it is to water life is usually measured in terms of its LCso This ts the lethal concentration of the substance in water at which 50 of test speci mens die within a fixed time period under test con ditions Generally speaking the higher the LCso value the less impact the substance will have on aquatic life Sometimes LCio and even LCo measurements are made or required These are much more demand ing with LCo indicating the concentration at which there has been no observable affect to the test spec
98. ing or decreasing the available orifice area and maintaining a con stant rate of flow These valves may be inserted at the inlet to each in line inductor or at some other point in the foam concentrate delivery line Several brigades have had foam making equipment modified so that the valve is incorporated within them It is of course essential that a metering device of the correct flow rating for the equipment Is used 20mm outlet with hermaphrodite coupling 20mm a niy outlet with ye hermaphrodite coupling wiliiecs Male instantaneous inlet d Inline Foam Injection Pelton Wheel As mentioned earlier high pressure losses in excess of 30 can be expected when using in line venturi inductors It is not unusual for this loss together with hose monitor and nozzle losses to add up to a total pressure loss that makes the per formance of some pieces of foam making equip ment ineffective particularly in terms of throw One alternative system is to make use of a pelton wheel driven positive displacement pump which will introduce foam from a storage tank or foam dam into the delivery hoses through a regulating valve This valve can be adjusted to suit the injec tion rate required and once set will inject at the required percentage regardless of pressure fluctua tions in the delivery hose The units can be sup plied with either fixed or adjustable induction rates to suit the circumstances
99. involving liquids or liquefiable solids Class C fires involving gases Class D fires involving metals Electrical fires are not included in this system of classification Cloud point The lowest temperature at which a liquid remains clear Usually only applicable to high expansion foam concentrates Combustible liquid Any liquid having a flashpoint at or above 37 8 C 100 F 82 Fire Service Manual Concentration Critical application rate Crude oil Density Dike area Discharge rate high expansion foam Drainage time Expansion ratio Film forming FFFP foam concentrates To achieve effective performance foam concentrates must be mixed to the concentration recommended by the manufacturer For each 100 litres of the required foam solution the foam concentrate must be mixed as follows Recommended Volume of Foam Volume of Volume of Concentration Concentrate Water Foam Solution litres litres litres l 99 100 3 3 97 100 6 6 94 100 The foam application rate below which a fire cannot be extinguished Petroleum in its natural state as extracted from the earth Consequently there are many different types of crude oil each with different characteristics and each yielding different quality products The various constituents ensure that crude oils general ly have wide ranging flash points with usually sufficient fractions or light ends to classify them as class A petroleum products
100. ion and greatly assist in the mixing in of air This helps to produce uniform sized stable foam bubbles of acceptable drainage and expansion characteristics Some manufacturers claim that for some low expansion foams such as P and FP complete for Firefighting Foam Technical Zt mation of stable foam bubbles should take approx imately 1 30th of a second However foam solu tion does not begin to form bubbles until it hits the side walls or obstructions approximately half way along the length of the branch Consequently tt is claimed the foam solution should be in the branch for a total of 1 15th of a second to form stable fin ished foam For main line use at flows of approxi mately 225 lpm a low expansion foam making branch in excess of metre in length would be required to give the required pass through time Some foam solutions produce bubbles more readi ly than others For instance SY NDET AFFF and FFFP foam solutions require less working and hence foam of adequate quality can be produced using shorter branches than are required by P or FP foam solutions Ultimately if foam working is excessive the foam becomes very stiff and loses its flow qualities for film forming foams this may impair there ability to produce an aqueous film on the surface of hydrocarbon liquids If not enough working 1s achieved the foam will be very quick draining have poor stability and be made up of foam bubbles of irregular size
101. ion other than rapid evacuation from the oncoming flow If monitors and hoses are immediately available they could provide sufficiently rapid knockdown On some fuels film forming foams are considered particularly effective at fast knockdown although other foams can have similarly rapid effects Another technique is to lay a band of foam at the lower end of the path of flow so that any pool that builds up will do so beneath a foam blanket For this type of application fluoroprotein or film form ing alcohol resistant foams might be considered most suitable because of their stability although other foams would also satisfactorily perform the task 74 Fire Service Manual The main method of combating running fires is by prevention Firefighters must be aware of any potential for a pool fire to breach or over spill its containment Firefighting efforts should be adjust ed to reduce such a risk for example minimising the use of cooling water which could drain into the contained pool and cause overflowing monitoring the integrity of containing bund walls and evacuat ing in advance any area which could possibly become inundated 6 3 6 Other Terms Various other terms are used for different types of fire and explosion incident such as BLEVE see Glossary of Terms Firefighting Foams at the rear of this Volume vapour cloud explosion gas flare etc These have not been covered separately since the use of firefighting foam is no
102. iscussed in the previous Section have a strong bearing on the tactics and techniques of using firefighting foam However the size shape and general appearance of a fire is also of particular importance when tackling class B or class C fires Firefighters often refer to spill fires pool fires and running fires and the variations in firefighting technique required to tackle each This Section describes these types of fire and how their characteristics can affect the approach to fire fighting These descriptions relate to ideal conditions which in practice are unlikely to occur exactly as described and in some Situations such as incidents involving aircraft more than one of these situa tions may occur simultaneously Even so they illustrate the principles involved 6 3 2 Spill Fires Spill fires occur in unconfined areas of flammable or combustible liquids with an average depth of around 25mm or less There is often variation in the depth of the spill due to unevenness of the sur face on which the liquid stands Because it is unconfined a spill fire may cover a very large area The main characteristic of spill fires is their rela tively short burning times If an average burn rate of 4mm of the depth of fuel per minute is assumed then most of the fuel involved in a spill fire will have burnt away within 7 minutes of ignition Such brief burn times are however unlikely to occur in practice Flammable liquid may remain in a ru
103. ity and to enhance foam ing properties preservatives to prevent the growth of bacteria and moulds stabilisers to help maintain foam bubble stability and anti freeze chemicals These all help to prevent various prob lems that could arise if only the basic chemical constituents of the foam concentrates were used Firefighting Foam Technical 7 In addition to the two main foam concentrate groups other specialised foam concentrates and water additives are available in particular Hazmat foam concentrates for vapour suppression of toxic odorous and or flammable materials Wetting agents for increasing the penetrating abilities of water Class A foam concentrates primarily for use on class A fires Fuel emulsifiers emulsion forming additives for use primarily on class B fires for firefighting and to prevent re ignition Note that P FP FFFP SYNDET and AFFF con centrates are often referred to as conventional foam concentrates in order to distinguish them from alcoho resistant foam concentrates and the specialised foam concentrates and water additives mentioned above There are many companies manufacturing foam concentrates and the quality of the products varies from manufacturer to manufacturer In addition the quality of a particular manufacturer s version of a foam concentrate may vary slightly on a daily basis due to acceptable variations in the base mate rials used and other
104. jet fuels The aqueous films produced are extremely thin typically less than a quarter of a millimetre thick and are unlikely to form on the surfaces of any hot fuels Some research carried out in America has indicated that film formation does not occur on aviation gasoline when at temperatures above i 60 C Consequently these thin films are unlikely to help in extinguishing fires in many flammable fuels that have had long preburns It must be stressed that film formation does not take place on all hydrocarbon fuels In such cases these foams must rely on the normal extinguishing mechanisms of foam blankets That is to exclude air from the fire reduce evaporation and generally cool the fire This may require more foam to be applied for a longer period of time than would normally be expected when using a film forming foam It is important to note that although alcohol resis tant foams produce aqueous films on some liquid hydrocarbon liquids they do not produce them on water miscible liquids As mentioned above the ability of a foam to form a film on a hydrocarbon liquid can be determined by measurements of the surface tensions of the foam solution and the hydrocarbon liquid These measurements are usually carried out in a labora tory However in firefighting situations the condi tions are likely to be very different This makes the conclusions of laboratory measurements generally inapplicable to most practical
105. lcohol resistant foams developed 1970s Further development of alcohol resistant foam concentrates to produce multi purpose foams for use at 3 on hydrocarbons and 6 on water miscible liquids Hazmat foams developed for the suppression of vapour from hazardous materials 1980s Development of alcohol resistant foam concentrates to produce AFFF AR alcohol resis tant AFFF Development of fluoroprotein foams to produce FFFP Film forming Fluoroprotein and multi purpose FFFP AR Alcohol Resistant FFFP foam concentrates A 1990s Development of alcohol resistant foam concentrates to produce versions that can be used at 3 concentration on both hydrocarbons and water miscible liquids Introduction of class A foam concentrates 1 3 How Foams Extinguish Fires Firefighting foam is much lighter less dense than all liquid fuels and so it floats on their surfaces The foam blankets that are formed help to knock down and extinguish these fires in the following ways By excluding air oxygen from the fuel surface By separating the flames from the fuel surface By restricting the release of flammable vapour from the surface of the fuel By forming a radiant heat barrier which can help to reduce heat feedback from flames to the fuel and hence reduce the production of flammable vapour By cooling the fuel surface and any metal surfaces as the foam solution drains out of the foam blanket
106. let pressure of 7 bar and is claimed by the man ufacturer to have a maximum horizontal range of 50 metres and a maximum height of throw of 18 metres Another example operates at approximate Figure 5 6 Portable foam monitor in use Photo West Midlands Fire Brigade 0 0 0 9 Figure 5 7 Photograph show ar ing the layout of a typical trailer mounted foam monitor Photo Angus Fire Armour Ltd Water inlets ly 4300 Ipm at 10 bar inlet pressure with a claimed throw of 60 metres and height of 24 metres The throw distances and heights provided by man ufacturers are often recorded at different monitor elevations and probably in still air conditions so care must be taken when making comparisons between different makes and types The quoted distances are likely to be reduced when the moni tors are used under operational conditions If at all possible before purchase or operational use this type of equipment should be operated at potential risk sites to ensure that acceptable throws and heights are achieved This is especially true of risks involving storage tanks where the heights of Foam concentrate inlet Gearing for elevation and depression Stabilising jack the tanks and the large distance between the mon itor possibly positioned on or below a bund wall and the tanks make the projection of foam into the tanks extremely difficult 5 2 6 MX Hand held Foam making Branch
107. liquid is a high flash point fuel the burn back rate of flames through the spray jet or stream of fuel leaking from the container may be less than the rate at which the fuel ts discharged from the leak In this situation the discharging fuel will not be on fire Consequently the fire can be extinguished with a foam blanket or water spray in a similar fashion to a pool fire the only additional precaution being to ensure that the level of fuel does not rise sufficiently to over spill the contain ment Sand bagging diversion channels and pumping out are all useful techniques to help pre vent breakdown of containment If on the other hand the burn back rate of flames through the spray jet or stream of fuel leaking from the container exceeds the rate at which the fuel is coming out of the container then the dis charging fuel will also be on fire It may be neces sary to use dry powder to extinguish fires in flow ing jets of liquid or gas in conjunction with foam application to the spreading fuel Water sprays are effective in reducing the heat output from burning jets although they will break down any foam blan ket already formed 6 3 5 Running Fires This term refers to the case when a burning liquid is moving down a slope on a broad front The situ ation is rare but extremely hazardous because of the rapidity with which objects and people in the path of the flow can be enveloped It is not possi ble to advise any course of act
108. lso be used to produce MX foam and these are likely to give dif ferent foam volume outputs S220 LX Hand held Foam making Branches a How They Work Figure 5 3 illustrates the principal features of a typical hand held LX foam making branch Designs vary and will incorporate some or all of these features The strainer is frequently omitted as often is the on off control DE a mY a a a aMi _ On off control valve Male Instantaneous coupling Foam solution Strainer Upstream orifice plate Turbulence chamber Air inlet holes Semi circular baffles Outlet nozzle Foam making tube Dispersal disk Downstream orifice plate Figure 5 3 Principal features of a Low Expansion foam branch pipe In the diagram are two orifice plates The upstream orifice is the larger of the two and its function is to create turbulence in the space between the two orl fice plates so that when the jet issues from the downstream orifice it rapidly breaks up into a dense spray The spray fills the narrow inlet sec tion of the foam making tube and entrains large quantities of air through the air inlet holes The downstream orifice is smaller and is calibrated to give the designed foam solution flow rate at the recommended operating pressure e g 225 Ipm at 7 bar branch pressure Most foam making branches have a narrow sec tion at the inlet end in which the air entrainment takes place and then a wider secti
109. ly on the foam concentrate in order to enable a valid comparison to be made It should also be noted that all of the standards referred to in this Chapter of the Manual are for primary aspirated foams only there are currently no standards available for determining the suitabil ity of foam concentrates for fire service secondary aspirated use When looking at the suitability of standard fire tests for particular fire service related applications the following questions should be addressed 3 3 2 Is the Fuel Commonly Encountered Operationally Petrol is the most likely fuel to be encountered operationally Fuels such as avtur avgas and hep tane are not as volatile as petrol and are generally easier to extinguish Avtur and avgas may be in regular use at airfields but are rarely encountered elsewhere Heptane 1s unlikely to be encountered operationally and is not representative of any fuel that 1s 3 3 3 Is the Fuel Reproducible Is the fire test fuel manufactured to a tight enough specification so that the burning characteristics of the fires are always similar The specifications for military and aviation grades of avtur and avgas can be strict which enables them to be used as test fuels Heptane is a very reproducible fuel and this is the main reason why it is used as the test fuel in many standards Various well defined grades of Heptane are available and the exact grade required for a particular standard fire test is normal
110. ly spec ified In Europe petro is produced to European stan dards that allow variations in formulation within fairly large margins This allows petrol to be pro duced economically but provides a fuel whose burning properties and effects on foam can vary considerably These variations make petrol unsuit able for use as a standard test fuel 3 3 4 How Long is the Preburn Preburn times 1 e the time from ignition of the fuel until the application of foam can vary from standard to standard Short preburns are unlikely to allow the fuel burning rate and heat output to stabilise and will not allow the tray sides enough time to become hot Longer preburns are more realistic and consequently the fires are likely to be more difficult to extinguish Preburns of around a minute are often used for hydrocarbon fuels This is a Compromise between fuel costs and fire sever ity Fires involving water miscible fuels take much longer to stabilise and so the longer the preburn the better 3 3 5 How Deep is the Fuel For hydrocarbon fires the fuel depth should be at least 25mm a spill fire see Chapter 6 Section 6 3 2 or preferably deeper This is likely to be a more realistic condition for the tests and will pro vide enough fuel for a reasonable preburn time and burnback test However it must be remembered that with an average hydrocarbon burning rate of 4mm per minute a 25mm depth of a typical hydro carbon fuel will only bu
111. making branches generally only mix rela tively small amounts of air into the foam solution Consequently these produce finished foam with low expansion LX ratios that is to say the ratio of the volume of the finished foam produced by the nozzle to the volume of the foam solution used to produce it is 20 1 or less Other equipment is available which can produce medium expansion foam MX with expansion ratios of more than 20 1 but less than 200 1 and high expansion foam HX with expansion ratios of more than 200 1 and possibly in excess of 1000 1 The following Sections describe in more detail some of the important factors of foam production that were introduced above 1 4 2 Percentage Concentration All foams are usually supplied as liquid concen trates These must be mixed with water to form a foam solution before they can be applied to fires They are generally supplied by manufacturers as either 6 3 or 1 foam concentrates These have been designed to be mixed with water as fol lows 6 concentrates 6 parts foam concentrate in 94 parts water 3 concentrates 3 parts foam concentrate in 97 parts water 1 concentrates part foam concentrate in 99 parts water Firefighting Foam Technical 3 1 concentrate is basically six times as strong as 6 concentrate and 3 concentrate is twice as strong as 6 concentrate However the firefighting characteristics of finished foam produced from 1 3 and 6
112. mance It 1s also very important to have compatibility of foam making equipment and induction equipment and just as importantly foam induction equipment must be checked regularly to ensure that it is operat ing correctly and giving an accurate rate of induction 1 4 3 Aspiration Once the correctly mixed foam solution has been delivered to the end of a hose line there are a num ber of forms in which it can be applied to the fire Generally foam application is referred to as being either aspirated or non aspirated A Fire Service Manual Aspirated foam is made when the foam solution is passed through purpose designed foam making equipment such as a foam making branch These mix in air aspirate and then agitate the mixture sufficiently to produce uniformly sized bubbles finished foam Non aspirated implies that no aspiration of the foam solution has taken place Consequently the term non aspirated foam is often used incorrectly to describe the product of a foam solution that has been passed through equip ment that has not been specifically designed to produce foam such as a water branch However the use of this type of equipment will often result in some aspiration of a foam solution This ts because air is usually entrained into the jet or spray of foam solution As it leaves the branch As it travels through the air due to the turbulence produced by the stream When
113. n and extinction performances when compared to those of film forming foams require to be well worked to make acceptable finished foam they must be used primary aspirated unsuitable for use with water miscible fuels although alcohol resistant FP is available for certain specialised applications c FFFP FFFPs were designed to exhibit a combination of AFFF and FP characteristics The intention was to produce a foam concentrate that had the knock down and extinction performance of AFFF combined with the good burnback resistance char acteristics of fluoroprotein However fire tests Reference 5 have indicated that although low expansion FFFP gives similar firefighting and burnback performance to AFFF the burnback performance is greatly inferior to that achieved by fluoroprotein and is generally not much better than AFFF Low expansion FFFP finished foams tend to have the following useful characteristics usable foam can be produced with minimal working manufacturers suggest that they can be used primary and secondary aspirated flow quicker than P and FP foams over liquid fuel surfaces quickly reseal breaks in the foam blanket and flow around obstructions This often results in very quick fire knockdown and extinction On some liquid hydrocarbon fuels these characteristics may be enhanced by the film forming capabilities of FFFP suitable for subsurface base injection moderate resistance to fue contami
114. n liquid under operational conditions see Chapter 4 Section 4 4 3 2 6 Effects of Freeze Thaw Freeze thaw tests are used to determine the effects on a sample of foam concentrate of several cycles of cooling it below its freezing point and then thawing it out Some standards require a selection of physical property tests to be carried out after the freeze thaw cycle The results of these are then compared with measurements made before the tests any variations must fall within certain limits Other standards simply require observation of the sample for evidence of solids crystals or sludge 3 2 7 Accelerated Ageing Accelerated ageing is intended to determine the effects on a foam concentrate of long term storage The test usually involves storing a sample of the foam concentrate at a high temperature e g 60 C for an extended period of time e g 7 days The foam concentrate is then allowed to cool and the effects on the foam concentrate are measured nor mally by comparing before and after physica property tests 3 2 8 Viscosity Viscosity is a measure of how well a liquid will flow see Chapter 2 Section 2 2 2 Liquids are generally classed as either being non Newtonian or Newtonian A low viscosity is often desirable because it improves the flow characteristics of a foam concentrate through pick up tubes pipework and induction equipment The viscosity of the foam concentrate is usually measured either at 20 C or at it
115. n the hosereels are off the foam concentrate flow should be zero If foam concentrate is not required during use then it should be possible to turn the supply off No water should flow into the foam concentrate container at any time O The system must work when pumping from the appliance water tank a pressure fed supply or open water The system should not adversely affect branch performance due to for instance high pressure losses The system should be capable of continu ous operation especially while the foam concentrate supply is replenished It should be possible to retrofit the system to appliances In addition to these the desirability of having foam solution passing through the appliance pump 1s also an important factor to be considered It is unlikely that any hosereel induction system will meet all aspects of this suggested operational requirement The only system at present that does not pass foam solution through the pump is the in line inductor However the use of this results in pressure drops in excess of 70 which would adversely affect branch performance Systems are often unable to maintain correct rates of foam proportioning over the range of flows like ly to be experienced on the fireground All have to be operated in very restricted ranges of flow and pressure in order to maintain accurate induction rates The outline of the operational requirement given above is a good starting point
116. nage times poor burnback resistance poor vapour suppression unsuitable for use with polar fuels f Alcohol Resistant Foam Concentrates AFFF AR and FFFP AR Low expansion finished foams produced from AFFF AR and FFFP AR alcohol resistant foam concentrates tend to have the following useful characteristics suitable for use on fires involving water miscible liquids such as alcohols and those petrol blends that contain high levels of alcohols and other similar fuel performance improvers suitable for use on hydrocarbon liquid fuel fires O usable foam can be produced with minimal working manufacturers suggest that they can be used primary and secondary aspirat ed on non water miscible fuels On water miscible fuels the foam solutions must not be applied non aspirated and also their use on these fuels when secondary aspirated cannot be recommended flow quicker than P and FP foams over liquid fuel surfaces quickly reseal breaks in the foam blanket and flow around obstructions This often results in very quick fire knockdown and extinction On some liquid hydrocarbon fuels these characteristics may be enhanced by the gi 9 film forming capabilities of AFFF film forming does not occur on water miscible fuels good resistance to contamination from hydrocarbon fuels so can be applied force fully to these if absolutely necessary Only gentle application techniques should be used when applying
117. nation although not as fuel tolerant when used on non water miscible fuels as alcohol resis tant film forming foams or FP foams and the following disadvantages d poor at sealing against hot objects poor foam blanket stability and very quick foam drainage times poor burnback resistance poor vapour suppression unsuitable for use with water miscible fuels Synthetic SYNDET SYNDET finished foams are versatile in that they can be used for firefighting at low medium and high expansion In the UK they are mainly used at medium and high expansion foams Firefighting Foam Technical 35 The following comments mainly relate to their use at low expansion in order to enable a comparison to made with all of the other foam types discussed However many of these comments are also rele vant for their use at medium and high expansion Low expansion SYNDET finished foams tend to have the following useful characteristics produce acceptable foam with minimal working must be used primary aspirated quick flowing which can assist in produc ing quick fire knockdown Medium and high expansion SYNDET foams do not flow as readily however the large volume of foam produced can achieve quick knockdown and extinctions very stable foam blankets with very slow foam drainage times Medium and high expansion SYNDET foams can be severely affected by wind they have the following disadvantages v
118. ncentrate induction rate to be between 5 4 and 6 6 Other levels of accuracy are often stated in stan dards and by equipment and foam concentrate manufacturers Discussions with these organisa Figure 5 13 A typical small water driven high expansion foam generator lA DEL tions may be necessary to ensure that these levels of accuracy are acceptable and will not affect the firefighting performance of the resulting foam or lead to unacceptable amounts of foam concentrate being wasted Some of the foam making equipment described in the previous Section is self inducing In other words the foam making equipment can pick up and mix foam concentrate with the water supply prior to producing finished foam Generally a pick up tube of a few metres length is used to connect the foam making equipment to a foam concentrate container This method of induction is not always satisfactory for the following reasons Control and operation of the induction system can be more carefully carried out at a safe distance from the fire Movement of self inducing foam making equipment is restricted due to the need to be close to a supply of foam concentrate Foam concentrate supplies have to be transported to the foam making equipment For these reasons foam concentrate is often intro duced into the water supply line some distance away from the foam making equipment The types of induction equipment most commonly used by th
119. ncentrate as an individual item The MIL F spec was designed by the US navy to assess the suitability of 3 and 6 18 Fire Service Manual aspirated AFFF firefighting foams for crash fire situations US Navy typical applications of AFFF include incidents on the flight decks of aircraft carriers where a quick knockdown of shallow spill fires is required to assist air crew survivability When purchasing foam concentrates it is important to have some background knowledge of these standards in order to decide whether the foam concentrates complying with them are likely to be suitable for fire service use Ideally the standards themselves should be obtained and evaluated It should be remembered that the methods and evaluation techniques used may vary considerably from standard to standard As a result it can be very difficult and unwise to compare results achieved by one foam concentrate when tested to one standard with those achieved by a second foam concentrate when tested to another standard In addition the results of standard small scale fire tests cannot be relied upon to predict the fire fighting performance of foam concentrates when used on large fires Generally foam concentrate standards consist of two main areas of testing Physical property tests Fire tests In Sections 3 2 and 3 3 of this Chapter physical property tests and fire tests are discussed in gener al terms Once the concentrate ha
120. nd to prevent reignition after extinguishment It should be remembered that if water 1s used for cooling it will break down any existing foam blan ket in that area allowing any remaining flames to burn back and preventing further blanket forma tion until the water application ceases The pool fire therefore requires a foam with a high fuel tolerance and heat resistance as well as fast flowing characteristics Adequate post fire security is also required 6 3 4 Spreading Fires Spreading fires can be described as unconfined spill or pool fires in which the liquid fuel 1s being continuously supplemented by a spray jet or stream from a ruptured tank or equipment The continuous supply of fuel often results in burning liquid flowing into inaccessible areas such as drainage systems and floor voids An early step in fighting a spreading fire is to stop the flow of product to the flames whenever possible Water spray provides an excellent screen behind which to approach the fire and close leaking valves for instance The flow from a storage vessel can also be stopped by water dis placement if there is sufficient freeboard above the source of the leak This method has been successful in the case of a ruptured storage tank line Water is pumped into the tank to raise the liquid fuel above the level of the outlet line so that water instead of product flows from the broken line Firefighting Foam Technical 73 If the flammable
121. neral As mentioned previously finished foam is usually classified as being either low medium or high expansion The expansion or more strictly the expansion ratio of a foam is the ratio of the vol ume of the finished foam to the volume of the foam solution used to produce it For example if 100 litres of foam solution were passed through a foam making branch and 800 litres of foam were produced then the expansion ratio of the foam would be calculated as follows Expansion ratio volume of foam volume of foam solution 800 litres 100 litres 8 1 This foam would also be referred to as having an expansion of 8 Typical firefighting foam expansion ratio ranges are less than or equal to 20 1 Low expansion Medium expansion greater than 20 1 but less than or equal to 200 1 High expansion greater than 200 Secondary aspirated foams generally have an expansion ratio of less than 4 1 1 5 2 Equipment Used For Generating Different Expansion Ratio Foams Primary aspirated low expansion foams are usually produced by using purpose designed foam making branches or mechanical generators Secondary aspirated low expansion foams are usu ally produced by using standard water delivery devices although some purpose designed large capacity monitors have been produced for this par ticular type of application see Volume 2 Medium and high expansion foams are usually pri mary aspirated through special
122. njection into pump inlet In line inductor Orifice plate amp diaphragm assembly CONSTAFLO MULTI CONSTFLO The basic principles of operation of these systems are given below This is followed by suggestions for an operational requirement for a system to induce additives into the high pressure hosereels of a first line appliance This operational requirement is then briefly compared with the typical performance of some existing hosereel induction systems b Premix Premix systems involve foam concentrate being mixed to the correct concentration with for instance the whole contents of an appliance water tank A true premix system is ready mixed in Firefighting Foam Technical 63 advance of use while a dump tank premix system drops foam concentrate into the appliance water tank only when required For a dump tank system the whole contents of the tank become a premix and there may be a significant wastage in foam concentrate if this 1s not completely used at an inci dent Conversely for a true premix system there may be problems in maintaining the correct foam solution concentration when topping up the tank c Round the pump A typical round the pump system 1s described ear lier in this Chapter in Section 5 3 Other similar systems are available for use in hosereel systems some of which use flowmeters valves and micro processor control These match the foam concen trate flow rate to the water
123. nly give the correct induction rate at one particular inlet pressure and flow e g at 7 bar and 225 lpm Operation other than at the pressure and flows rec ommended by the manufacture will result in inac curate foam pick up rates or no foam pick up at all Fixed and variable rate in line inductors are avail able Fixed rate inductors can only be used at one induction rate generally either 1 3 or 6 The induction rate of variable in line inductors can usually be varied anywhere between 1 and 6 by the use of a control knob Figure 5 15 Practically all in line inductors are designed to induce the foam concentrate through a pick up tube placed in a drum or similar container They can however also be used in conjunction with a pressurised foam concentrate supply Figure 5 16 Foam concentrate percentage control Figure 5 15 An inline variable inductor The advantages of the use of in line inductors are generally the cheapest induction system available simple robust and with few moving parts quick deployment redeployment on the fire ground foam solution does not pass through the pump or appliance pipework making clean up easier and reducing the possible corro sive effects of the foam solutions The disadvantages of in line inductors are for optimum performance the inductor must be matched to the foam making equipment for optimum performance the inductor must be matched to the t
124. nt foam concentrate types chemicals are added Various types of surface active agents or surfac tants are added to many firefighting foam concen trates These are used to reduce the amount of fuel picked up by the finished foam on impact with fuel i e they increase fuel tolerance and to increase the fluidity of the finished foam 1 e they make it easier for finished foam to flow over some fuels and other surfaces Surface active agents are also used as foaming agents because they readily produce foam bubbles when mixed with water Consequently hydrocar bon surface active agents or as they are more com monly known synthetic detergents are the main constituents of synthetic based foam concentrates Surface active agents are also used in some protein based foams Surface active agents can help to reduce the sur face tension of water This not only helps in the formation of foam bubbles but also increases the ability of the water to penetrate and spread This is particularly important when fighting class A fires because it can help water to penetrate and cool the burning material In film forming foam concentrates surface active agents form an aqueous film of foam solution which in certain conditions can rapidly spread over the surface of some burning hydrocarbons to aid knockdown and extinction Other chemicals may also be added to foam concentrates These include corrosion inhibitors solvents to reduce viscos
125. nt Foam Concentrates AFFF AR and FFFP AR Environmental Impact of Firefighting Foams General Foxicity Biodegradability Chapter 5 Equipment Sl 52 52l 5 2 2 5 2 5 2 4 S29 5 2 6 32l 5 2 8 5 29 S SRAI Diz 5 5 3 5 3 4 50 5 3 6 General Foam Making Equipment General LX Hand held Foam making Branches a How They Work b LX Foam making Branch Performance LX Hand held Hosereel Foam Unit LX Foam Generators LX Foam Monitors MX Hand held Foam making Branches LX and MX Hand held Water Branch Snap on Attachments MX Foam Pourers HX Foam Generators Foam Concentrate Induction and Injection Equipment General In line inductors Round the pump Proportioners Pressure Control Valves Pressurised Foam Supply a General b Distribution Manifold c Metering Devices d Inline Foam Injection Pelton Wheel e Pre induction Units f Direct Coupled Water Pump Hosereel Foam Induction and Injection Systems a General b Premix c Round the pump d Injection in to Pump Inlet e In line Inductors f Suggestions for an Operational Requirement for a Hosereel Induction System Compressed Air Foam Systems CAFS Methods For Checking Foam Solution Concentration as Produced by Foam making Equipment Firefighting Foam Technical 33 33 34 34 35 35 35 36 36 37 37 37 38 39 39 39 40 40 4l 42 43 da 45 46 46 46 50 50 51 52 56 56 56 60 60 61 61 62 63 63 63
126. nual Figure 5 22 Pressurised foam concentrate supply being got to work Photo Surrey Fire and Rescue Service be used a second manifold can be added to the first one either directly or via additional lengths of hose The shut off valves on the manifolds are opened or closed according to the number of in line inductors to be supplied c Metering Devices In order to ensure the optimum output of foam making equipment the correct amount of foam concentrate should be fed to the inductors at all times To ensure this a metering device or con stant flow valve as it 1s also known is inserted into the line There are many of these types of devices available D Figure 5 23 A typical distribution manifold Female instantaneous outlet a ae Sr One example of a metering device consists of a flexible ring resting on a tapered seating At low pressure the ring is fully expanded giving the maximum orifice opening As the pressure rises the ring is compressed and forced gradually down the tapered seating progressively decreasing the size of the orifice The combination of increased pressure and decreased orifice size maintains a constant flow Figure 5 24 In another example see Figure 5 25 a neoprene diaphragm shaped like a plug is located above a profiled orifice When subjected to pressure varta tions between and 14 bar this diaphragm flexes onto the orifice thereby increas
127. o sometimes recommended in order to reduce these effects Sealing oils can also be used to cover the surface of the foam concentrate although pressure vacuum vents will still be required The materials used for the construction of the con tainers and associated fittings pumps etc should also be carefully considered to ensure that corro ston and a possible reduction in firefighting per formance does not occur see Section 2 2 3 above The positioning of storage containers should also be a major consideration to ensure that the foam concentrates are not subjected to temperatures beyond the storage limits recommended by the manufacturers see Section 2 2 4 above Containers that are refilled before being complete ly emptied may cause foam quality and firefight ing performance problems even if the same type and make of foam concentrate is used The foam concentrates may be incompatible see Section 2 2 1 above and the mixing of different ages of foam concentrate may produce unwanted side effects such as sedimentation and sludge Ideally containers should be completely emptied cleaned and dried before they are refilled Methods of transporting the foam concentrate and or their containers to the fireground and then distributing the foam concentrate to foam making equipment also need to be carefully considered Fixed bulk storage containers will require ade quately specified and sized pumps and or outlets especially for gravit
128. oam concentrate in water at the appropriate concentration Foam with a short drainage time i e the liquid content of the foam takes a short period of time to drain out of the foam the foam breaks down quickly Freeze point Froth over Hazmat Heat resistance High expansion foam HX Hydrocarbon fuel Induction Inductor Eductor Induction rate pick up rate Inline inductor Knockdown Low expansion foam LX Mechanical foam Medium expansion foam MX Minimum use temperature Monitor The highest temperature at which a material can exist as a solid Overflow of a non burning flammable liquid from a container due to the thermal expansion of the liquid or violent boiling on top of and within the upper layers of the liquid due to the presence of small quantities of water see also boil over and slop over A proprietary trade name used to describe special types of foam which can be used to suppress the vapour production of certain hazardous materials toxic odorous and or flammable The ability of a foam blanket to withstand the effects of exposure to heat Finished foam of expansion ratio greater than 200 Fuels based exclusively on chains or rings of linked hydrogen and carbon atoms Hydrocarbon fuels are not miscible with water The entrainment of foam concentrate into the water stream A device used to introduce foam concentrate into a water line The percentage at which foam concentrate is propo
129. of Finished Foams 4 14 1 General The following Sections highlight the typical characteristics of low expansion finished foams produced from each of the main types of foam concentrate described in Chapter 2 These charac teristics relate mainly to their use on hydrocarbon liquid fuel fires although other comments are made concerning for instance their compatibility with water miscible fuels The terms used here have been explained earlier in this or the previous Chapters see also the Glossary of Terms Table 4 1 overleaf enables a quick comparison to be made of the typical firefighting related characteris tics of low expansion finished foams made from each of the main foam types The contents of this table are intended to provide information on typical performance during general fire service use in par ticular when used against hydrocarbon spill fires The table should be read in conjunction with the contents of the remainder of this Section which provide more details of the characteristics for each foam type In addition some comments regarding the suitability of different foam concentrate types for use in tackling storage tank fires are given in Volume 2 of the Manual It should be remembered that there are many com panies manufacturing each of the different foam concentrate types The quality of foam concen trates produced will vary from manufacturer to manufacturer and often different quality versions of the same foam type
130. om the bottom O Three samples One from the top one from the middle and one from the bottom of the container Samples should be collected in clean seal able containers Each sample should be at least 1 litre and should completely fill the container Once the samples have been collected the collection con tainers should be sealed and labelled with the date and details of where the sample was taken from At least two samples should be taken from each sam pling location One sample should be sent to the testing organisation and the other should be kept for further testing should this be required Do not write on the sample container the type and concentration of foam concentrate that is in the container the testing organisation should be able to determine this from the results of their tests If this information differs from the actual contents then it is an indication that further investigations or tests may need to be carried out to identify the cause of the discrepancy Care should be taken when collecting from the bottom of a container due to the possible accumu lation of sediment from rust and degradation Firefighting Foam Technical 23 products This sediment should be prevented from entering the sample container as it may lead to test results that are not representative of the whole con tents of the container If only one sample is to be tested then it is preferred that this should be drawn from the con taine
131. ombination of chemicals can as well as producing a foam blanket allow a very thin vapour sealing film of foam solution to spread over the surface of some liquid hydrocarbons FFFP foam concentrates are usually available for use at 3 or 6 concentrations They are primari ly intended for the production of low expansion foam although they can also be used to produce medium expansion foam Also due to their film forming properties they can be applied secondary aspirated and can be used to tackle class A fires FFFP foam concentrates are not recommended for the production of high expansion foam FFFP foam concentrates are more expensive than P and FP foam concentrates As with P and FP foam concentrates consideration should be given to constructing bulk storage con tainers from materials such as epoxy coated carbon steel GRP or polyethylene 2 13 Synthetic Based Foam Concentrates a Synthetic Detergent SYNDET SYNDET foam concentrates were developed from early synthetic detergent foams and are based on a mixture of anionic hydrocarbon surface active agents solvents and foam stabilisers SYNDET foam concentrates are versatile as they can be used to produce low medium and high expansion foams They can also be used on class A and class B fires In the UK their use is usually limited to medium and high expansion foams However in other European countries such as Germany and Sweden SYNDET foam is used for low
132. on in which the foam forms The wider section of the foam making tube sometimes contains improvers e g semi circular baffles gauze cones which are designed to work the foam solution in order to produce longer draining finished foam The drawback of using improvers is that the extra working of the foam that they cause uses energy from the foam stream resulting in a reduction in the distance that the finished foam can be thrown At the outlet the branch is reduced in diameter to increase the exit velocity thus helping the finished foam to be thrown an effective distance The design here is crucial too narrow an outiet produces back pressure which results in less air entrainment and finished foam of very low expansion ratio and very short drainage times If the outlet is too large the expansion is higher but the throw is reduced Some branches may also contain flow straighten ing sections at the nozzle to reduce turbulence at the outlet of the branch These assist in forming a coherent rope of finished foam with little fall out of foam along its trajectory However these tend to considerably reduce the throw of the branch For foam making branches without flow straightening sections considerable amounts of foam can fall out of the stream along their trajectory resulting in a greatly reduced foam volume actually arriving in the area of impact b LX Foam making Branch Performance It is generally recognised that the
133. ormances of these indicating that if adequate amounts of water can be applied to all areas of a wood fire it will perform just as well as a primary aspirated or secondary aspirated foam when used in the same conditions Medium and high expansion foam have been advocated for indoor use on class A fires The confinement provided by the walls of buildings allows the foam to accumulate into a thick blan ket and also protects the foam from being torn apart by the wind The mechanism put forward for extinguishment is that the foam cuts down the movement of air which supports combustion There is a cooling effect as water from the foam evaporates and the steam generated will also tend to reduce the oxygen level in the air sur rounding the fire If the foam blanket is deep enough it will exert enough downward pressure to enable it to refill holes opened up when the foam is destroyed by the heat from the fire Materials and structural members that would otherwise be exposed are shielded from heat radi ation by the foam Although high expansion foam can be effective the main practical drawback is that firefighters cannot be sure that the fire has been extinguished It can be dangerous to enter a deep foam blanket to track down the seat of a fire since there is a chance of sudden exposure to heat and products of com bustion Under some conditions the fire can con tinue to burn for a considerable period at a reduced rate supported by the air r
134. otein based foam concentrates were of low acute toxicity However some AFFF and AFFF AR foam concentrates were also found to be in this low acute toxicity band 4 15 3 Biodegradability Biodegradability of a substance is a measure of how quickly it is broken down by bacteria Bacteria in the environment will break down and eat the substance extracting oxygen from the sur rounding water as they do so Measurements of biodegradability are made by carrying out two different tests and comparing their results One test provides a measure of the Chemical Oxygen Demand COD This is the total amount of oxygen required to degrade a set amount of foam the lower the COD the less oxygen that is stripped from the environment The second test provides a measure of the Biochemical Oxygen Demand BOD This is an indication of the foam concentrate s ability to con sume that amount of oxygen within a specified time period usually 5 days referred to as BODs Most of the data issued by foam manufacturers consists of biodegradability values in terms of BODs COD as a percentage The higher the per 38 Fire Service Manual centage the higher the biodegradability of a foam the quicker the foam is broken down The Water Research Council see above found that in most environmental hazard assessments high biodegradability is considered desirable However it has been found that the main environ mental impact of the use of foam is th
135. over the surface of a fuel and around obstructions Film formation the ability of the finished foam to form a film that spreads over some hydrocarbon liquid fuels Fuel tolerance the ability of the finished foam to resist mixing with and hence contamination by the fuel Edge sealing the ability of the finished foam to seal against hot metal surfaces Foam blanket stability drainage time an indication of how well the finished foam blanket retains its liquid content and hence how stable and long lasting it is Also included are the suitability of finished foams for base injection finished foam quality the compatibility of various finished foams with each other and with dry powders the typical firefighting characteristics of each of the individual types of foam identified in Chapter 2 particularly when used on liquid hydrocarbon fuel fires It should be remembered that other factors such as type of fuel equipment and application methods also have a considerable effect on the performance of finished foams These areas are discussed in later Chapters and the operational aspects of applying foam are discussed in Volume 2 of the Manual 4 2 Working Working refers to the action of the internal parts of foam making equipment on the foam solution stream as it passes through the equipment The internal parts can include gauzes and baffles which obstruct the flow of the foam solut
136. p tured fuel container and burn for a considerable time continuous leakage may replenish the spill or numerous deep localised burning pools of fuel may form over a large area 6 3 3 Pool Fires Pool fires occur in confined pools of flammable or combustible liquids which are deeper than 25mm but not as deep as the contents of storage tanks A pool fire may cover a large area depending on the volume of the fuel source and the area of the con fined space It may take the form of a bunded area in a tank farm or a hollow pit or trench within which flammable liquid has collected from a rup tured process vessel road or rail tanker The difference between pool fires and spill fires is that pools may depending on depth continue to burn for a considerable period of time As a result firefighters are more likely to encounter a well developed fire burning evenly over a large area rather than the more isolated scattered fires which are characteristic of an unconfined spill Foam may also be subject to more fuel contamination if forceful application is used due to the depth of the fuel Consequently techniques such as playing the foam stream against a solid surface and allowing the foam to run onto the fire may be both desirable and a practical possibility if suitable surfaces are available The sustained high levels of heat output may demand more effort to be made in cooling exposed Structures both to minimise damage during the fire a
137. pression can be achieved using secondary aspi rating equipment with film forming alcohol resis tant foam concentrates However they claim that these should be used at 2 to 3 times their recom mended concentration for application to hydrocar bon liquids e g used at 9 concentration instead of their recommended 3 However most brigades are unlikely to have equipment capable of proportioning at rates higher than 6 It should be noted that the standard film forming foam concentrates i e AFFF and FFFP form foam blankets that drain rapidly in order to quick ly form films on the fuel surface Consequently these foam blankets will need to be replenished at very frequent intervals if adequate vapour suppres sion is to be maintained Primary aspirated alcohol resistant film forming foams require less frequent replenishment due to their much longer drainage times 4 5 Fuel Tolerance Fuel tolerance describes how resistant a foam is to mixing with a fuel during application In general foams should be applied as gently as possible to the surface of a fuel to reduce the amount of mix ing that takes place Plunging a foam stream directly into a fuel will cause fuel to be mixed in with the foam If a fire is present then it 1s inevitable that this foam and fuel mixture will burn causing partial destruction of the foam blanket However some foams are more resistant to mixing with fuel than others P foams have poor fuel tolerance and
138. r after the contents have been thoroughly mixed together 3 4 3 Typical Physical Property Tests Although a wide range of tests may be carried out typically the following physical property tests will be included when manufacturers and test houses determine the condition of stored foam concentrates a Specific Gravity Relative Density The limits of specific gravity for foam concen trates are normally stated tn the manufacturers data Sheets Specific gravity measurements that are higher than the manufacturers limits indicate that the foam concentrate has become more concentrat ed probably due to evaporation Measurements that are below the manufacturers limits indicate that the foam concentrate may have been diluted by water in storage dilutions of greater than 10 may require that all of the foam concentrate in the container be replaced Changes in the specific gravity of foam concentrates may also indicate dilution or contamination by other substances See this Chapter Section 3 2 2 for more information on specific gravity b pH Acidity Alkalinity The limits of pH for foam concentrates are nor mally stated in the manufacturers data sheets pH values outside of these limits can indicate that the foam concentrate has been contaminated in some way e g mixed with other foam concentrates has been broken down by micro organisms and or has degraded due to incorrect storage See this Chapter Section 3 2 3 for more informa
139. r has falsified results it is always possible that an individual could act upon misplaced zeal in the future Some manufacturers will test any foam concen trate not just those they produce Consequently if funds allow it may be advisable to send samples to q k n more than one manufacturer in order to obtain sev eral test reports for comparison Independent test houses offer an alternative means of having foam concentrates tested However before allowing them to carry out work always ensure that they have previously analysed foam concentrates and that they can carry out the full range of tests to the required standard In order for the amount of deterioration that has taken place to be quantified it is necessary to have The manufacturer s data sheet from the time of purchase for the particular foam concentrate to be tested The results of the routine quality control tests originally carried out by the manufac turer during production on the particular batch or batches of foam concentrate to be tested This information will normally include the results of physical property tests and in some instances the results of fire tests All manufacturers gather quality con trol test data during production and they will normally make it freely available on request at the time of purchase However in order to make the best use of this information it is extremely important that batch num bers are recorded on stora
140. ranch Snap on Attachments Snap on attachments are available for use with some hosereel and main line water branches which enable primary aspirated LX and MX foam to be produced Generally the foam produced by these attachments is not very well worked making it less stable i e has much shorter drainage times and less effective than that produced by purpose designed primary aspirating foam branches 5 2 8 MX Foam Pourers In addition to the MX hand held foam making branches some free standing MX foam pourers are also available These are much larger than the hand held models have higher flow requirements and hence produce greater volumes of foam However as their name suggests finished foam pours out of them rather than being projected They have been designed to stand on their integral legs for the unattended delivery of MX foam into bunded areas such as those surrounding fuel stor age tanks They operate in a similar way to the hand held MX foam branches described above Typical models of MX foam pourers have nominal flow requirements of from 600 lpm to 1800 Ipm when operated at 2 5 bar inlet pressure The foam outputs of these are claimed to be approximately 24m3 min and 72 m min respectively at these operating conditions This is at an expansion ratio of approximately 40 1 5 2 9 HX Foam Generators High expansion foam generators are designed to be used with SYNDET foam concentrate only and usually produce fini
141. rea of the piston which is subjected to pressure on the upstream side is one fifth of the area of the piston on the downstream side so the forces acting on the piston wil balance when the downstream pressure is one fifth of the upstream pressure If the upstream i e hydrant pressure increases the downstream side will experience a proportion ally greater pressure increase This will immedi ately cause the piston to move closing the butter fly and reducing the flow through the valve there by reducing the downstream pressure until the 5 1 ratio is restored If the hydrant pressure falls the reverse process will occur 5 3 5 Pressurised Foam Supply a General At a large incident requiring perhaps several large foam monitors bulk supplies of foam concentrate will be required In these circumstances the con ventional system of inducing the concentrate via a pick up tube may be impractical for the following reasons It may not be feasible to use foam concen trate drums to supply the inductor because of the frequency with which they would have to be refilled or replaced The use of open topped portable dams may not be entirely satisfactory because when using some systems the foam concentrate tends to aerate and this can interrupt the i Figure 5 19 A typical pressure control valve with cutaway drawing and schematic diagram 9 Control valve balanced Ratio of area of piston face 5 1
142. reel is connected to an adaptor at the top of the unit and water is supplied at between 2 and 10 5 bar A small proportion of the water is diverted to fill a completely deflated flexible bag within the con tainer Inflation of the bag displaces the foam con centrate via a siphon tube the concentrate entering the main water stream and passing to an integral LX foam making branch to give a jet of primary aspirated foam The unit is controlled via an on off valve on the adaptor Figure 5 4 Hand held Hose reel Foam Unit Foam making branchpipe When operated at 3 5 bar with a flow rate of 46 lpm the manufacturer claims that the unit will pro duce foam with an expansion of approximately 8 5 2 4 LX Foam Generators As an alternative to a foam making branch a LX foam generator may be used This when inserted in to a line of hose induces appropriate amounts of foam concentrate and air into the water stream to generate finished foam which is then delivered through the hose to a water type branch for appli cation as aspirated foam The foam concentrate is induced using the same principle as that of an in K we Hose Reel Adaptor Yr Fill 4 Swe Syphon tube Flexible bag Foam concentrate line inductor see below and the air is drawn in through orifices adjacent to the water inlet The equipment can only work against limited back pressure so the length and size
143. res should all be tightly controlled in order for the fire tests to be repeatable and to enable the results to be satisfactorily compared with previous tests Large variations in temperature can lead to very different extinction and burnback results Cooler tempera tures are likely to lead to quicker extinction times and longer burnback performances Wind speed also needs to be carefully controlled little or no wind will help to produce better more reproducible tests and results indoor tests are preferred 3 3 9 What Burnback Test is Used In order to test the security of the foam blanket a burnback test is required Burnback tests where the burnback flames are near to or actually impinge on the foam blanket are much more test ing Burnback tests which also involve a burning fuel in a metal container can help to assess the sealing capabilities of foam blankets against very hot materials 3 3 10 When are the Fire Tests Carried Out Are the fire tests only carried out when the foam concentrate is initially tested for compliance with the requirements of a standard or are they carried out on a regular basis i e each manufactured batch quality control Are were the fire tests car ried out by an independent test house or were they carried out by the manufacturer 22 Fire Service Manual Regular fire testing can indicate the continuing suitability of foam concentrates for that task Some standards only require the fire t
144. ressure into hose lines without the use of in line inductors are also briefly discussed below these are pelton wheel in line foam injection pre induction units direct coupled water pump J 9 Figure 5 21 Diagrammatic layout of an incident requiring large quantities of foam concentrate supplied from a bulk foam carrier Pressurised concentrate line carrying 108 litres min Pressurised foam concentrate line carrying 54 litres min centrate Pressurised foam concentrate line carrying 54 litres min 1 x 1800 litres min foam monitor aon foam i j i E i La i til si b F N 4 x 900 litres min inline inductors Firefighting Foam Technical 59 b Distribution Manifold Various designs have been devised by brigades some incorporating a metering device Figure 5 23 shows a typical distribution manifold which con sists of a standard male instantaneous coupling leading to a manifold having two controlled outlets with 20 mm hermaphrodite couplings one on each side and a full bore on off valve The manifold finally has a standard female instantaneous cou pling at the other end This type of manifold is capable of feeding one or two in line inductors through 20 mm hose each line passing up to 70 litres of foam concentrate per minute If more than two in line inductors need to 60 Fire Service Ma
145. rface active agents with concentrate additional stabilisers They are multipurpose foams in that they can be used at low medium and high expansion Venturi A constricted portion of a pipe or tube which will increase water velocity thus momentarily reducing its pressure It is in this reduced pressure that foam concentrate is introduced The pressure difference across the venturi can be used to force foam concentrate into the water Viscosity This is a measure of how well a liquid will flow Liquids are generally classed as either being non Newtonian or Newtonian A low viscosity is often desirable because it improves the flow characteristics of a foam concentrate through pick up tubes O pipework and induction equipment Viscosity will also vary with foam concentrate type and with concentration AFFF foam concentrates at 3 and 6 oncentrations tend to be the least viscous closely followed by P FP and FFFP foam concentrates at 6 AFFF at 1 and SYNDET foams P FP and FFFP foam concentrates at 3 concentration are appreciably more viscous than these The alcohol resistant foams are often the most viscous although recent developments have dramatically reduced the viscosity of some products In addition the viscosity of all foam concentrates will vary with temperature and may be affected by the age of the foam concentrate Manufacturers often state the viscosity of their products when measured at 20 C lower temperatures will result
146. rn for around 6 minutes Fire tests involving water miscible fuels should have a much greater depth This is because their extinction can be aided by the dilution of the fuel with the applied foam solution Most standard fire tests involving hydrocarbons require there to be a depth of water a water base in the tray This helps to ensure a consistent depth of fuel over the whole area of the tray and helps to prevent heat damage to the fabric of the fire tray Fire tests involving water miscible type fuels must not have water bases because these will dilute the fuel making it easter to extinguish 3 3 6 What is the Application Rate The application rate should be above the critical application rate see Chapter 7 Section 7 2 but should not be too high If a high application rate is used then it is likely that the fire will be extin guished very easily even with poor quality foam concentrates The application rate should certainly not be any higher than the minimum recommend ed application rate for spill fires given in this Manual see Chapter 7 Section 7 3 3 3 7 How is the Foam Applied Some standards involve applying foam gently via a back plate Although it is recommended that foam should be applied gently when used opera tionally this is not often possible The better stan dards for foam concentrates for fire service use are those which require the foam to be applied force fully to the surface of a burning fuel i
147. rtioned in to water by an inductor in order to produce a foam solution Normally this is 1 3 or 6 An inductor inserted in to a hose line in order to induce foam concentrate prior to the water reaching the foam making branch The ability of a foam to quickly control flames Knockdown does not necessarily mean extinguishment Finished foam of expansion ratio of less than or equal to 20 1 Foam produced by a physical agitation of a mixture of water foam concentrate and air Finished foam of expansion ratio greater than 20 1 but less than or equal to 200 1 The lowest temperature at which the foam concentrate can be used at the correct concentration through conventional equipment such as inline inductors and other proportioning devices A large throughput branch water or foam making which is normally mounted on a vehicle trailer or on a fixed or portable pedestal Firefighting Foam Technical 85 Multipurpose foam concentrates Newtonian liquids Non aspirated Unaspirated Non Newtonian pseudo plastic liquids Oleophobic Over the top foam application pH Acidity Alkalinity Polar solvent Pour point amp 6 Fire Service Manual Another name given to alcohol resistant foam concentrates The viscosity of Newtonian liquids remains the same no matter how quickly or slowly they are flowing see also non Newtonian pseudo plastic liquids Most non alcohol resistant foam concentrates such as AFFF
148. s The measure used for this is pH which 1s on a scale of 1 to 14 If the pH of a liquid is lower than 7 then it is an acid if it is higher than 7 it 1s an alkaline A liquid with a pH of 7 is referred to as neutral being neither acid nor alkaline pure water has a pH of 7 Acidic liquids are usually the most corrosive to metals and alloys particularly those containing iron such as carbon steel or cast iron Strong alka line liquids can attack aluminium and zinc Firefighting foam concentrates can contain a high percentage of water in some the water content can be as much as 80 Consequently most foam con centrates are nearly neutral with pH values of between 6 5 and 9 0 The limits of pH of a partic ular foam concentrate are normally given by the manufacturer and are determined in laboratories by using pH meters In addition to the effects of pH surface active agents can increase corrosion mainly due to their cleaning and penetrating properties although other chemical actions can also take place Foam concentrate manufacturers should always be consulted on the best materials for use with their products However testing Reference 2 has indi cated that UPVC 60 40 brass 70 30 brass and stainless steel may be the best materials for use in storing the types of foam concentrate most often used by the UK fire service 1 e AFFF AFFF AR FFFP FFFP AR P FP and SYNDET Zinc for galvanising was found to be unacceptable for
149. s the hazard can be reduced by sup pressing the released vapour until the spill can be neutralised and disposed of Some of the conventional firefighting foams dis cussed above may be used for vapour suppression on spills of flammable and combustible products Also a certain amount of success has been achieved with them on toxic spills However many chemicals destroy firefighting foams either by reacting with them or by extracting the water from foam blankets Alcohol resistant foams can be effective on some toxic spills and flammable combustible and water miscible liquids Hazmat foam concentrates have been designed to be effective on products which destroy foams by chemically reacting with them Versions of these foam concentrates are available that have been for mulated to be resistant to either extreme acidity or extreme alkalinity They are often used to produce medium expansion foams with optimum expan sion ratios of around 60 1 Developments in this area include an additive for use in conjunction with one particular alcohol resistant foam concentrate that significantly slows down the drainage rate of the finished foam to pro duce a very stable foam blanket that lasts in excess of 12 hours This can be used on hazardous mate rials and is easily washed away with a water spray after use However additional equipment is required to mix the additive into the foam solution line on application If there is doubt concerning the
150. s although recent developments have dramatically reduced the viscosity of some products In addition the viscosity of all foam concentrates will vary with temperature and may be affected by the age of the foam concentrate Manufacturers often state the viscosity of their products when measured at 20 C lower temperatures will result in much higher viscosity Manufacturers may also quote a Lowest Use Temperature or Minimum Use Temperature for their foam concentrates The definition of these terms varies but they should be used to indicate the temperature below which foam concentrates can not be used through induction systems However these figures must be treated with some caution because foam concentrates above these low tem peratures may still have high viscosity which will prevent them being picked up at the correct rate by most foam concentrate induction systems Induction equipment should be checked for accu racy both when the foam concentrate is at the low est temperature at which it expected to be used and Firefighting Foam Technical 13 at normal operating temperatures With some foam induction systems the use of high viscosity foam concentrates and some non Newtonian pseu do plastic foam concentrates will result in little or no foam concentrate being picked up 2 2 3 Corrosion An initial indication of how corrosive a liquid may be can be made by looking at how acidic or alka line it i
151. s been purchased it should be stored and used as recommended by the manu facturer or supplier see Chapter 2 Section 2 2 However the foam concentrate will eventually deteriorate and so it is important that foam stocks are periodically tested to ensure that their perfor mance remains acceptable Section 3 4 of this Chapter discusses periodic testing including typi cal physical property and fire tests that might be performed and also provides information on the collecting of representative foam concentrate sam ples from storage containers 3 2 Physical Property Tests of Foam Concentrates 3 2 1 General Physical property tests often include laboratory measurements of parameters such as pH acidi ty alkalinity viscosity specific gravity sediment and the effects of accelerated ageing Standards generally contain well defined methods and equip ment for the measurement of these properties The results of these tests can be used to compare the properties of the foam concentrate with mini mum maximum requirement limits set within stan dards or with previously tested foam concentrates The data provided by these tests can be used by manufacturers as bench marks for checking the consistency of later manufactured batches of foam concentrates quality control The measurements can also be used for compari son purposes in order to determine the condition of foam concentrates after long periods of storage see this Chapter Section
152. s illustrated for this pur pose in Figure 5 14 must be included in the foam concentrate pick up line to prevent water flowing back into the foam concentrate container There will always be a pressure drop across the inductor of at least 30 of the inlet pressure This is necessary for the inductor to work properly The pressure drop is due partly to turbulence and part ly to the energy loss involved in the induction process Pressure drops in excess of 70 have been recorded for hosereel in line inductors see this Chapter Section 5 3 6 If the back pressure at the outlet of the inductor is too high this may result in the pressure drop across the inductor being less than required In such circumstances the velocity of the water trav elling through the inductor nozzle would not be high enough to enable the pressure in the induction chamber to fall below atmospheric and so the inductor would fail to work High back pressure can be caused by connecting too many lengths of hose between the outlet of the inductor and the foam making equipment or through differences in elevation In order for it to operate effectively it is important to match the pressure and flow characteristics of 52 Fire Service Manual Hermaphrodite induction coupling Foam solution Female instantaneous outlet the foam making equipment with that of the induc tor Inline inductors are usually identified by their nominal flow rate at
153. s minimum use temperature 3 3 Foam Concentrate Standard Fire Tests 3 3 1 General Standard fire tests that is those fire test methods that are contained in various foam concentrate standards e g British European and International standards are used to assess the firefighting 20 Fire Service Manual performance of foam concentrates under closely controlled but artificial conditions The results of these tests can be used to compare the performance of foam concentrates with minimum maximum requirements within the standards or with previ ously tested foam concentrates Typically timings are recorded to 90 extinction 99 extinction complete extinction and 25 or 100 burnback The surface area of the test fires varies but it is usually in the region of 0 25m to around 4 5m Small standard fire tests are used by some manu facturers for quality control purposes during pro duction although fire tests are usually considered to be environmentally unfriendly inconvenient costly and time consuming to perform Results of standard fire tests cannot be used to pre dict the firefighting performance of foams opera tionally although they do at least indicate that the foams can put out fires They can also be used to ensure that the firefighting performance of foam concentrates has not deteriorated due to age cor rosion contamination etc However this requires that the same test method and equipment have been used previous
154. s taken place Manufacturers should be consulted if there are any doubts Freeze protected and non freeze protected versions of the same brand can be mixed but there will obviously be a reduction in the freeze protection of the foam concentrates 222 Viscosity Viscosity is a measure of how well a liquid will flow A low viscosity is often desirable because it improves the flow characteristics of a foam concentrate through pick up tubes pipework and induction equipment Liquids are generally classed as either being non Newtonian or Newtonian Many alcohol resistant foam concentrates are con sidered to be non Newtonian pseudo plastic liq uids For these liquids as their flow increases their viscosity decreases and so they flow more easily Consequently getting them to flow initially can be difficult but once flowing their viscosity reduces to a more acceptable level In contrast the viscosity of Newtonian liquids such as most non alcohol resistant foam concen trates remains the same no matter how quickly or slowly they are flowing Viscosity will also vary with foam concentrate type and with concentration AFFF foam concen trates at 3 and 6 concentrations tend to be the least viscous closely followed by P FP and FFFP foam concentrates at 6 AFFF at 1 and SYN DET foams P FP and FFFP foam concentrates at 3 concentration are appreciably more viscous than these The alcohol resistant foams are often the most viscou
155. shed foam they must be used primary aspirated very slow flowing and stiff protein foams do not quickly reseal breaks in the foam blanket or seal around obstructions These are some of the major reasons for the slow fire knockdown and extinction performance of protein foams very poor fuel tolerance when applied forcefully to the surface of a fuel This is the main reason for very slow fire knock down and extinction performances unsuitable for use with water miscible fuels unsuitable for subsurface base injection b FP Low expansion finished foams produced from FP foam concentrates tend to have the following use ful characteristics flow quicker than P foams over fuel surfaces reseal breaks in the foam blanket and seal around obstructions These properties assist in producing fire knockdown and extinction performances that are quicker than that achieved by P good fuel tolerance so they can be applied reasonably forcefully if absolutely necessary produce acceptable fire knockdown and extinction performance although generally slower than film forming foams good sealing properties against hot metal surfaces form stable foam blankets with slow foam drainage times very good burnback resistance very good vapour suppression suitable for subsurface base injection and the following disadvantages do not flow as well as film forming foams This often results in slower knockdow
156. shed foams of expansion ratios of 200 1 to 1200 1 Air is blown through the generator by a fan foam solution is sprayed into the air stream and this is directed onto the surface of a fine net screen The air blowing through the net wetted with foam solu tion produces finished foam with a mass of bub bles of uniform size which like the MX foam pourers is poured rather than being projected Finished Premix Solution i K Figure 5 9 Principle of operation of a medium expansion foam branch pipe Firefighting Foam Technical 47 The generator fan may be powered by 4 petrol engine an electric motor a water turbine which utilises the flowing foam solution immediately prior to it being sprayed into the generator The water turbine driven generators are obviously more suited to applications in areas where there 1s a flammable risk Most HX foam generators can also be used as smoke extractors Figure 5 10 shows in diagrammatic form the essential principles of HX foam generators Some generators require a separate in line inductor but others are self inducing and some are capable of being operated either way Some water turbine driven generators incorporate a by pass system With the by pass closed all of the foam solution passing through the generator is used both for driving the turbine and for foam production This produces a lower expansion HX finished foam containing a
157. sk should be obtained from the manufacturer of the alcohol resistant foam concen trate to be used Typical recommended foam application rates for water miscible liquid fires range between 4 and 13 litres per minute per square metre However it is recommended that the minimum application time for a spill of water miscible fuel should be 15 min utes and for tanks involving these fuels it should be a minimum of 60 minutes On water miscible liquids application must be such that the foam blanket is delivered gently onto the liquid surface without submerging the foam or agitating the liquid surface If some submergence and agitation is unavoidable the foam blanket will be destroyed at a high rate and much higher appli cation rates and application times will be required 7 4 Optimum Application Rate The optimum application rate is sometimes referred to as the most economical rate It is the rate at which the minimum overall quantity of foam solution is needed to extinguish a fire This rate usually lies somewhere between the cnitical application rate and the recommended minimum application rate The optimum application rate is not the rate at which the quickest extinction is achieved To achieve the quickest extinction time rates in excess of the optimum application rate are required However the small reductions in extinc tion times achieved by these increased application rates are at the cost of large increases in the use of reso
158. t e g foam making branches foam making generators etc Foam concentrate induction and Injection equipment e g in line inductors etc Specialised foam equipment for fighting storage tank fires 1s not covered here but is described in Volume 2 of the Manual Much of the information contained within this Chapter has been obtained from manufacturers This information should only be used as a guide to performance and may not reflect actu al performance under operational conditions Equipment should always be tested under realistic conditions before purchase to ensure that all oper ational requirements and performance criteria are met In addition the induction injection and foam making equipment should be checked at regular intervals using operational pressure flow condi tions and hose lengths to ensure that the foam making system is working correctly and that the required quality of foam is being produced see Chapter 4 Section 4 12 and this Chapter Section 5 5 5 2 Foam Making Equipment 5 2 1 General The primary aspirating foam making equipment used by brigades can be divided into the following main categories LX hand held foam making branches LX hand held hosereel foam unit LX foam generators LX foam monitors MX hand held foam making branches LX and MX hand held water branch snap on attachments MX foam pourers HX foam generators The above equipment is available in various sizes req
159. t directly involved O Firefighting Foam Technical Chapter Chapter 7 Application Rates 7 1 General The application rate of a foam onto a fire is nor mally expressed as the amount of foam solution in litres per minute to be applied to every square metre of the total area to be covered with foam The following five terms are often used to describe various foam application rates and it is important to know the difference between them they are Critical Application Rate Recommended Minimum Application Rate Optimum Application Rate Overkill Rate Continued Application Rate The following Sections describe the meanings of these various terms The most important of these for operational use is Recommended Minimum Application Rate 7 2 Critical Application Rate The critical application rate is the application rate below which a fire cannot be extinguished When applied at below this critical rate the finished foam will be broken down by both the fuel and the heat of the fire to such an extent that a complete foam blanket will not be able to form over the sur face of the fuel 7 3 Recommended Minimum Application Rate 7 3 1 General The Recommended Minimum Application Rate 1s the minimum rate at which foam solution is rec ommended to be applied to a fire The rate assumes that all of the foam made from the foam solution actually reaches the surface of the burning fuel The recommended minimum applica
160. ther conditions breakdown of foam due to flames before it reaches the fuel surface and loss of foam due to the thermal convection currents caused by the fire For storage tank fires these rates need to be increased by up to 60 to account for foam losses In addition it is recommended that application rates should be reviewed if after 20 30 minutes application there has been no noticeable reduction in the intensity of the fire In practice the recommended minimum applica tion rates are of great importance in pre planning the resources needed for a foam attack It has a direct bearing on the quantity of concentrate and water required and also should dictate the amount of delivery equipment i e appliances monitors branch pipes proportioners and hoses 7 3 3 Fires Involving Water miscible Class B Liquids Application rates for water miscible fuels vary considerably depending on the following factors the type of fuel the depth of fuel the type of foam the manufacturer of the foam the method of foam application Some of the most widely used water miscible liq uids include Alcohols e g Methanol Ethanol Isopropanol Ketones e g Acetone Methyl Ethyl Ketone Vinyl Acetate Acrylonitrile Due to the large number of water miscible fuels in use and the varying firefighting performance of different foams on each of them information on the recommended application rates for a particular water miscible ri
161. thods to be used Drainage times and expansion ratios can only be reliably compared if the same type of foam concentrate measuring equipment foam making equipment and measurement methods are used 4 13 Compatibility of Finished Foams 4 13 1 With Other Finished Foams Generally speaking all types of finished foam can be used together on a single fire although the order of application may affect their performance For example film forming foam would be better applied first for a quick knockdown and extinction of a hydrocarbon fuel fire followed by an applica tion of FP foam to provide good burnback resis tance Applying these foams in reverse order would result in the partial breakdown of the FP foam blanket and hence reduced burnback resis tance due to the film forming foam blanket quick ly draining with the resulting falling liquid droplets bursting the FP foam bubbles 4 13 2 With Dry Powder Some finished foams will react unfavourably with certain fire extinguishing powders if used at the same incident The manufacturer should be asked whether there are any particular incompatibles to their product Firefighters should remember to consult the industrial MOD CAA brigades etc in their areas as well as neighbouring local authority brigades where appropriate to find out what dry powder types they are using Foam concentrate manufacturers should then be contacted for advice on compatibility 4 14 Typical Characteristics
162. time it takes for a 25 area of the fuel surface to become re involved in flames The longer the 25 burnback time the better the burnback resistance of the foam blanket Some foams such as P FP and the alcohol resis tant film forming foams have significantly greater burnback resistance and hence give longer burn back times than AFFF FFFP and SYNDET Generally the more foam applied to a fire after extinction has occurred the better the burnback resistance will be However if a foam blanket is left over a period of time and allowed to drain without being replenished the burnback resistance of the blanket will be significantly impaired 4 10 Water miscible Fuel Compatibility Alcohol resistant foam concentrates have been developed to deal with fires involving water mis cible liquids such as alcohols and some petrol blends containing high levels of alcohols and other similar fuel performance improvers These and the finished foams that they produce are described in Chapter 2 Section 2 1 4 4 11 Suitability For Subsurface Base Injection Some finished foams can be introduced via spe cial equipment into the bases of large storage tanks The foam then floats to the surface of the contents of the tank This has the advantage that the finished foam is not carried away by the updraught created by large fires and is not deterio rated by flames on the way to the surface of the fuels However foams that are used for subsurf
163. tion on pH c Sediment Sludge Sediment will tend to sink to the bottom of con tainers when stored over a long period of time 24 Fire Service Manual Consequently care should be taken when obtain ing samples from the bottom of a container to ensure that a representative sample is obtained see above The maximum sediment content of a foam concentrate is normally stated in the manufacturers data sheet When stored correctly foam concentrates should only contain very small amounts of sediment High levels of sediment can indicate that the foam concentrate has been contaminated in some way e g mixed with other foam concentrates has been broken down by micro organisms and or has degraded due to incorrect storage See this Chapter Section 3 2 4 for more information on sediment d Spreading Coefficient Film forming foams which no longer provide a positive spreading coefficient when measured have either been contaminated or have significant ly degraded See this Chapter Section 3 2 5 for more information on spreading coefficient 3 4 4 Periodic Fire Tests Any fire tests of stored foam concentrate samples that are carried out by manufacturers or indepen dent test houses are likely to involve significant cost However it should be remembered that the main reason for using foam concentrates is to extinguish fires and so this type of testing is the best way of determining whether the foam concen trate remains suita
164. tion rate is based on the critical application rate see above with an additional safety margin to help to take into account factors such as variations in the quality of foam concentrate variations in the quality of finished foam produced some of the detrimental effects of forceful application The Home Office recommended minimum appli cation rates for use by the UK fire service for fires involving water immiscible class B liquids are given in Section 7 3 2 below Advice Is given con cerning the application rates for fires involving water miscible class B liquids in Section 7 3 4 below 7 3 2 Fires Involving Water immiscible Class B Liquids Tables 7 1 and 7 2 give the minimum application rates of foam solution recommended by the Home Office for use by the UK fire service when using manual firefighting equipment to apply low and medium expansion foam to fires involving water immiscible class B liquids Also recommended durations of foam application are included in the tables It should be noted that the figures given in Tables 7 1 and 7 2 relate to minimum foam solution application rates and times and assumes that all of the finished foam produced from the foam solution actually reaches the surface of the liquid on fire These rates should not be considered as being definitive allowances must be made to compen sate for losses due to circumstances such as fall out of finished foam from the foam stream
165. to the deliveries while a small amount returns to the proportioner where more concentrate 1s induced and the sequence is repeated Isolating valves can be incorporated to cut off the system when foam is not required Various other valves in this sort of system are incorporated to drain the foam concentrate tank flush the system connect a pick up tube in case a foam supply other than that contained in the appliance foam concentrate tank needs to be used Although this proportioner has an operating pres sure range of between 3 and 14 bar the recom mended pressure is 7 bar with a water requirement of 193 Ipm The induction rate for a round the pump inductor has to be selected by a dial calibrated in litres per minute Consequently the operator must know the flow rate at which the foam equipment is operating in order to be able to calculate the correct pick up flow rate for the concentration of foam concentrate being used For instance if the supply to the foam making equipment is 193 Ipm and 3 concentrate is being used then the inductor dial should be set as follows Figure 5 17 Diagrammatic layout Foam concentrate Water al Foam Solution Foam _ high concentration concentrate f Tank Foam Solution Variable Foam proportioner concentrate tank valve Round the pump isolating valves Drain flushing pickup tube valve 54 Fire Service Manual working concentration deliveries a
166. ts of the hosereel tubing were taken in to account the total pressure loss was in excess of 90 Consequently using this in line inductor at the appliance pump connected to the branch with 3 lengths of 19mm hosereel tubing and at a pump pressure of 26 bar resulted in a branch pressure of less than 3 bar Suggestions for an Operational Requirement for a Hosereel Induction System The following are suggestions for inclusion in an operational requirement for a system to induce all types of foam concentrates into the high pressure hosereels of a first line appliance It should be capable of inducing all types of foam concentrate at selected concentra tions within the range 1 to 6 For alco hol resistant foams it must be possible to select 3 concentration for hydrocarbon fires and 6 concentration for alcohol fires The accuracy of induction should be main tained over the varying flow and pressure conditions from one or two hosereels up to a total flowrate of 300 Ipm The induction system should be accurate to plus or minus 10 of the correct concen tration that ts for 1 concentrate induction rate to be between 0 9 and 1 1 for 3 concentrate induction rate to be between 2 7 and 3 3 for 6 concentrate induction rate to be between 5 4 and 6 6 When foam concentrate is required for the hosereels only ideally no foam solution should be available from the main deliveries Whe
167. uipment will produce foam of significantly higher shear Strength In addition in primary aspirated equip ment the more working that takes place the high er the shear strength of the finished foam 4 4 Film Formation The term film formation ts often used and applies to AFFF AFFF AR FFFP and FFFP AR foam concentrates Under certain conditions the foam solutions and finished foams produced from these foam concentrates have the ability to produce an aqueous film which spreads over the surface of some liquid hydrocarbon fuels On these particular fuels the film is said to help cool the surface of the burning liquid to reduce the hydrocarbon evapora tion rate seal in the vapour at the surface of the fuel and hence deplete the supply of fuel to the flames Consequently they may assist in the knockdown and extinction of fires in these partic ular fuels The fluorocarbon surface active agents and foam ing agents that combine to produce film forming foams produce a foam solution that has a very low surface tension This allows a thin film to be formed on and to spread across some liquid hydrocarbon fuels The main factor which influ ences the effective formation of this film on a hydrocarbon s the surface tension of that hydro carbon Film forming foams tend to be much more effective on liquid hydrocarbons that have a much higher surface tension than the foam solution High surface tension fuels include kerosene diesel oils and
168. uiring from less than 50 litres per minute to over 15 000 litres per minute of foam solution Some types of foam making equipment are fitted with a means of picking up foam concentrate at the equipment via a length of tube these are known as self inducing Some types of these operate at fixed induction rates e g 3 or 6 while others have control valves which enable them to be quickly adjusted to pick up foam concentrate at a range of concentrations It 1s also usually possible to turn off the induction facility completely so that the foam making equipment can be used with pre mix foam solutions see below With all other types of foam making equipment the foam concentrate must be introduced into the water stream at an earlier stage usually by some form of induction or injection equipment see this Chapter Section 5 3 this results in the production of a premix foam solution In other words the foam concentrate and water have been mixed Firefighting Foam Technical 39 together prior to arriving at the foam making equipment A less often used method of producing a premix foam solution is by mixing the correct proportions of water and foam concentrate in a container prior to pumping Some brigades have used this method in the water tanks of water tenders Secondary aspirated foam is often produced using standard main line and hosereel water branches However some purpose designed secondary aspi rating
169. urces such as water foam concentrate etc For some applications such as those involving air crashes quick extinction times are of the utmost priority and can be considered a worthwhile use of these resources 7 5 Overkill Rate There is a limit to how quickly a fire can be extin guished when using firefighting foam Once the application rate has reached a certain level higher application rates give no improvements in extinc tion time they only result in a wastage of resources These higher application rates are known as overkill rates Firefighting Foam Technical TI 7 6 Continued Application Rate Various standards quote lower rates for continued application after a fire situation has been extin guished These rates should be sufficient to main tain the integrity of the foam blanket and are often around 50 of the minimum recommended foam application rate 78 Fire Service Manual Firefighting Foam Technical References L CFBAC JCFR Report 19 Trials of 10 Medium and High Expansion Foams on Petrol Fires P L Parsons 1982 ra SRDB Publication 12 90 Chemical Effects of Additives on Fire Appliances and Associated Equipment B P Johnson 1990 gt CFBAC JCFR Report 31 Additives for Hosereel Systems Trials of Foams on 40m Petrol Fires J A Foster 1988 4 CFBAC JCFR Report 79 Class A Additives K Bosley 1997 Di FRDG Publication 2 93 A Comparison of Various Foams when used against Large Sc
170. ving constant flow Graph showing the performance of a 4 5 litre min Maric valve trate motor that are linked via a common shaft The water motor is connected into the main water feed line to the foam making equipment As water passes through this motor it turns and drives the foam concentrate motor which injects foam con centrate into the water stream discharging from the outlet of the water pump The capacities of the motors are carefully chosen so that the correct per centage of foam concentrate 1s injected into the water line Due to the linkage between the motors the percentage concentration remains correct over a wide range of flows through the water motor Typical portable versions cover various flow ranges between 200 and 2000 litres per minute at a maximum pressure of 15 bar The induction rate is usually either fixed at 3 or is adjustable from 3 to 6 Disadvantages of this type of system are that they are expensive and that they can produce pressure drops of 25 to 30 of the inlet pressure J Figure 5 25 Principle of operation of the Mobrey constaflo oO valve 1 Single valve 2 Multiple valve 5 3 6 Hosereel Foam Induction and Injection Systems a General There are four categories of system most often available for use by brigades for the induction of foam concentrates into high pressure hosereels Reference 8 They are Premix systems Round the pump systems I
171. w brigades take advantage of these wetting agent properties by using AFFF not only for class B fires see below but also they claim to make better use of limited water supplies on Class A fires It is claimed that the increased cost in agent is often justified by reduced water damage to the property Tests have indicated that in some circumstances the addition of some foam concentrates to water can help in reducing the severity of a Class A fire when compared to the use of water alone Reference 10 In particular when applied by Spray to wooden crib fires secondary aspirated AFFF and to a slightly lesser extent FFFP AFFF AR and SYNDET performed significantly better than water Several wetting agents were also tested but they did not perform much better than water These results seem to indicate that wetting proper ties may not alone quickly and effectively deal with Class A fires involving wood The smothering characteristics of the foams may also be helping In fact this is the principle under which American Class A foams have been developed see Chapter 2 Section 2 1 7 Firefighting Foam Technical 69 During these tests because of the size and shape of the fires some areas of the cribs were not ade quately reached by the spray Consequently tests were also performed using jet applications of water primary aspirated AFFF and secondary aspirated AFFF There was little difference in the firefighting perf
172. will be available from the same manufacturer Consequently the following Sections indicate the typical characteristics of fin ished foams produced from each of the foam types Firefighting Foam Technical 33 Table 4 1 Typical Characteristics of Low Expansion Finished Foam CHARACTERISTIC Requires to be well worked Foam Flow Fluidity Film forming on some hydrocarbon liquids Hydrocarbon Fuel Tolerance Flame Knockdown Edge Sealing Extinction Foam Blanket Stability Drainage Time Burnback Resistance Vapour Suppression Foam Application Water miscible Fuel Compatible Suitable for Hydrocarbon Subsurface Injection Notes to Table 4 1 FOAM TYPE P FP FFFP FFFP AR SYNDET AFFF AFFF AR grades and the level of repeatability of the tests Yes Yes No No No No No Da a a i a a a a RT No No w Yes I W D 1 mm ox m mo oD Wm mo a mo oO oom i hei me fo ee oo mm om in mn iW mm mo 8 oD a Oo on im iin i af i tr G Mm mon wo 1 oo on cx i LX Lx LX ie EX MX MX MX MX MX MX SA T HX JA SA fier No n Yes No Re Yes Ha Wana eae es y This table summarises the typical characteristics that can be expected from good quality low expansion finished firefighting foams when used to fight some flammable hydrocarbon liquid fuel spill fires The characteristics of finished foam will vary depending on factors such as fuel application technique equipment and the quality of the foam concentrate used T
173. y fed systems to ensure foam concentrate supplies are loaded into mobile units in the shortest possible time Mobile units should also have adequately specified and sized pumps and outlets to ensure quick delivery of the foam concentrate when on the fireground The materials of construction of the containers and associated fit tings on the mobile units should also be chosen with the corrosive and other effects of foam con centrates in mind Firefighting Foam Technical 15 Firefighting Foam Chapter Technical Chapter 3 Foam Concentrate Standards and Periodic Testing 3 1 General Foam concentrates should be purchased that com Manufacturers usually produce their foam concen ply with standards that are relevant to their use by trates to comply with one or more foam concen the fire service They should also be tested periodi trate standards The following foam standards are cally to ensure that they have not degraded e g due often quoted in manufacturers literature to ageing accidental dilution or contamination Standard BS EN 1568 Part Part 2 Part 3 Part 4 ISO 7203 1995 9 Part Part 2 Part 3 DEF STAN 42 40 DEF STAN 42 41 ICAO CAA CAP 168 UL 162 MIL F 24385 ia SEE ee ee Title Fire Extinguishing Media Foam Concentrates British European Standard Specification for medium expansion foam concentrates for surface application to water immiscible liquids
174. ype and concentra tion of foam concentrate in use pressure losses through the inductor in excess of 30 can be expected at the normal working pressure range when using matched foam making equipment accuracy of proportioning will vary with pressure Figure 5 16 An inline inductor top connected to a pressurised foam concentrate supply bottom Photo Mid and West Wales Firefighting Foam Technical 53 rl 5 3 3 Round the pump Proportioners This type of inductor is connected across a pump and can either be a permanent fixture in the appli ance or with adapters and connecting hoses stand alone Two typical available models are one with a nominal induction flow range of 0 45 lpm and the other with a nominal induction flow range of 0 90 Ipm The induction flow can be altered within these ranges by the use of a rotating grip handle on the body which has a scale calibrated in litres per minute Figure 5 17 shows a typical round the pump pro portioning system where an appliance has a built in foam concentrate tank When pumping begins some water flows to the deliveries and some pass es to the proportioner The proportioner induces foam concentrate to produce a rich foam solution which passes back to the suction side of the pump Before re entering the pump the foam solution mixes with a fresh intake of water and is conse quently diluted to the required concentration Most of it then passes
175. ypically the addition of stabilising additives and inhibitors to help prevent corrosion resist bacterial decomposition control viscosity and improve their shelf life Chemical additives can include salts of iron and calcium sodium chloride and solvent The starting materials for production which pro vide the protein base product include soya beans corn gluten animal blood horn and hoof meal waste fish products and feather meal Protein foam concentrates are inexpensive and are usually manufactured for use at 3 or 6 concen trations Versions are available that can be mixed with sea and fresh water They are only intended for the production of low expansion finished foams In the past protein foam concentrates have been widely used by industry the fire service the armed forces and aviation authorities throughout the world They have now been largely superseded by fluoroproteins and film forming foam concen trates although large stocks are still sometimes held Often protein foam concentrates do not contain corrosion inhibitors as the concentrate 1s not con sidered to be particularly corrosive However incidents have indicated that some corrosion has taken place in unprotected carbon steel bulk stor age containers Consequently materials such as epoxy coated carbon steel GRP Glass Reinforced Plastic and polyethylene should be considered for the storage of protein foam concentrate b Fluoroprotein FP FP

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