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IS 14624-2 (2012): Safety of laser products, Part 2: Safety of Optical

1. NOTE 2 If the person or organization is using the OFCS for a communications application in a manner other than as designed by the manufacturer then that person organization assumes the responsibilities of a manufacturer or installation organization 3 4 hazard level the potential hazard at any accessible location within an OFCS It is based on the level of optical radiation which could become accessible in a reasonably foreseeable event e g a fibre cable break It is closely related to the laser classification procedure in IEC 60825 1 3 5 hazard level 1 hazard level 1 is assigned to any accessible location within an OFCS at which under reasonably foreseeable events human access to laser radiation in excess of the accessible emission limits of Class 1 for the applicable wavelengths and emission duration will not occur 3 6 hazard level 1M hazard level 1M is assigned to any accessible location within an OFCS at which under a reasonably foreseeable event human access to laser radiation in excess of the accessible emission limits of Class 1 for the applicable wavelengths and emission duration will not occur whereby the level of radiation is measured with the measurement conditions for Class 1M laser products see IEC 60825 1 NOTE If the applicable limit of hazard level 1M is larger than the limit of 2 or 3R and less than the limit of 3B hazard level 1M is allocated 3 7 hazard level 2 hazard level 2 is assigned to any accessibl
2. The 3 s shutdown for restricted areas is also consistent with 4 8 1 if one assumes that any failure of the system within a restricted area would be of an accidental nature and the 3s limit for shutdown would be an acceptable time period after the reasonably foreseeable event It is also highly unlikely that in this time period a person can get within 100 mm and position collimating optics be adversely exposed One must also keep in mind that optical signals are attenuated as they move down the fibre so the output at the failure in the restricted area may be considerably lower than at the transmitter or amplifier c Controlled locations Persons working in locations with controlled access must have received adequate training in laser safety which should include an understanding that viewing a broken fibre should not undertaken unless the system has been properly inactivated Rationale to Clause D 5 Annex D is informative The use of the term recommended may be incorrectly construed as forbidding the use of alternative methods of analysis The method of fault analysis and the adoption of a suitable safety level is the prerogative of the user 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 IS 14624 Part 2 2012 IEC 60825 2 2005 Bibliography IEC 60812 Analysis techniques for system reliability Procedures for failure mode and effects analysi
3. The maximum permitted FIT rate should be assigned as the upper limit of a SIL 1 level system From Equation D 1 and Figure D 4 above it can be seen that the minimum requirement i e the maximum acceptable FIT rate would be 4 x 106 FITs for a continuously diagnosed system with a mean time to repair MTTR of 24 h 104 FITs for a system with a MTTR of 1 year and 500 FITs for a system without continuous diagnostics FIT rate specifications can similarly be determined for other consequence risk levels see the IEC 61508 series Table D 13 FIT rates from example above FIT Rate Safety Consequence M4 M2 M3 integrity Continuous Frequent No level diagnostics testing monitoring SIL 1 Serious permanent injury to one or lt 4x106 lt 104 lt 500 more persons death to one person e g retinal damage small fire C3 D 6 Suggested working practices The following working practices may be regarded as examples of good practice and are recommended when working with OFCS Different working practices may apply in different circumstances D 6 1 General working practices The following working practices may be regarded as good practice when working on an OFCS Viewing fibre Do not stare with unprotected eyes or with any unapproved collimating device at the fibre ends or connector faces or point them at other people Viewing aids Use only approved filtered or attenuating viewing aids Fibre ends Any single or multiple fibre e
4. forced air cooling and status indication h spatial separation of multiple lines carrying duplicated signals i modification protection e g plausibility check of signals or detection by automatic start up tests For further information and details to the above mentioned methods see IEC 61508 5 Parts 2 and 3 D 5 6 1 8 Fit rate determination The reliability of the APR system is a continuum that is dependent on the responsible use and maintenance of these systems For APR functions with a very low FIT rate there is no maintenance of the APR function needed if the product is taken out of service within the specified lifetime of the APR function For all other systems the APR unavailability and consequently the FIT rate is dependent on the possibility that any failure of the APR can be detected and the operator alerted in a reasonable time for repair as well as the responsiveness of the operator to respond to any alarms that would indicate a failure in the APR Since equipment manufacturers do not have control over the maintenance of their systems it may be useful to propose specific FIT rates rather than the combination of SILs and mean time to repair Figure D 4 Manufacturers are likely to supply APR systems that either 1 have frequent or continuous diagnostic testing proof testing or 2 are not tested or monitored For continuous diagnostic testing monitoring and alarming it is likely that a failure in optical fibre commu
5. the requirements of 4 6 1 apply Additionally the explanatory text shall bear a statement of the maximum output of laser radiation after operation of the APR function where applicable and the associated wavelength or wavelength range 4 6 3 Markings for groups of connectors Groups of connectors such as patch panels may be marked as a group with just a single clearly visible location hazard level marking rather than having each connector individually marked If a group of connectors is housed within an enclosure and it is a foreseeable event that exposure to optical radiation above hazard level 1M could result from accessing the enclosure then a marking shall be clearly visible both before and after the access panel is removed This may require the use of more than one marking 4 6 4 Indelibility requirements for safety markings Any marking required by this standard shall be durable and legible In considering the durability of the marking the effect of normal use shall be taken into account Compliance is checked by inspection and by rubbing the marking by hand for 15s with a piece of cloth soaked with water and again for 15s with a piece of cloth soaked with petroleum spirit After this test the marking shall be legible it shall not be possible to remove marking labels easily and they shall show no curling The petroleum spirit to be used for the test is aliphatic solvent hexane having a maximum aromatic content of 0 1 by volume a
6. Amendments are issued to standards as the need arises on the basis of comments Standards are also reviewed periodically a standard along with amendments is reaffirmed when such review indicates that no changes are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of BIS Catalogue and Standards Monthly Additions This Indian Standard has been developed from Doc No LITD 11 3155 Amendments Issued Since Publication Amendment No Date of Issue Text Affected BUREAU OF INDIAN STANDARDS Headquarters Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002 Telephones 2323 0131 2323 3375 2323 9402 Website www bis org in Regional Offices Telephones Central Manak Bhavan 9 Bahadur Shah Zafar Marg 2323 7617 NEW DELHI 110002 2323 3841 Eastern 1 14 C 1 T Scheme VII M V I P Road Kankurgachi 2337 8499 2337 8561 KOLKATA 700054 2337 8626 2337 9120 Northern SCO 335 336 Sector 34 A CHANDIGARH 160022 260 3843 260 9285 Southern C I T Campus IV Cross Road CHENNAI 600113 2254 1216 2254 1442 2254 2519 2254 2315 Western Manakalaya E9 MIDC Marol Andheri East 2832 9295 2832 7858 MUMBAI 400093 2832 7891 2832 7892 Branches AHMEDABAD BANGALORE BHOPAL BHUBANESHWAR COIMBATORE DEHRADUN FARIDABAD GHAZIABAD GUWAHATI HYD
7. High demand or continuous mode covers those safety related systems which implement continuous control to maintain functional safety e g a pressure regulator valve For a SIL Level 1 system the target failure rate for a hazardous situation is between 1071 and 10 2 This target failure rate can be achieved by several solutions Examples include APR mechanical solutions and external risk reduction In this example APR is chosen and the probability that APR fails to reduce the power should be less than 0 1 see Table D 11 Table D 11 SIL values from 7 6 2 9 of IEC 61508 1 Safety integrity Low demand mode of operation level Average probability of failure to perform its design function on demand 210 5 to lt 10 4 210 3 to lt 10 2 gt 10 2 to lt 10 1 34 IS 14624 Part 2 2012 IEC 60825 2 2005 Concerning random hardware failures the SIL level or probability of failure of an automatic power reduction system is the APR unavailability If the APR is continually monitored with alarms to alert to a malfunction of the APR or periodically tested this unavailability is determined by both the APR equipment reliability and the operator repair time mean time to repair or MTTR in the event of an APR failure Equipment reliability is often expressed as FIT rate failures in 109 hours Consider the following equation SIL level APR unavailability 1 te MTTR 9 10 D 1 hus aea a0 MTTR where SIL level is fail
8. OTDRs typically operate at Class 1 so no potential hazard is present at such sources However higher power systems have a longer range and may require Class 1M Class 3R or Class 3B OTDRs to detect the break Also OTDR signals may be amplified to a higher Class if sent through an optically amplified system Except for turnkey systems designed for use in unrestricted locations it is important that a laser safety professional or the OFCS operator decide for each location or for the entire span of a network the hazard level that should be permitted consistent with the level of laser training provided to their staff and others who could access their network Hazard level 1M or hazard level 3R are often chosen because workers would be instructed not to use any optical collimating instruments that would increase the hazard and typically they would have no need to examine the fibre at a close range Hazard level 3B is acceptable in controlled locations with proper labelling and connector conditions This subclause will examine APR under several circumstances in systems with optical amplifiers on a readily accessible fibre in a splice tray ata fibre optic connector ona fibre not readily accessible in a submerged buried cable in restricted and unrestricted locations inthe case of ribbon cables For upper limit values of typical wavelengths see Clause D 3 and Table D 1 D 4 3 1 Optical amplifiers Optical amplif
9. be assigned if no automatic power reduction feature would be present the irradiance or radiant exposure during the maximum time to reach the lower hazard level specified in 4 8 1 1s for unrestricted 3 s for restricted or controlled locations shall not exceed the irradiance or radiant exposure limits MPE For controlled locations the measurement distance is 250 mm for this subclause only 4 8 3 Conditions for tests and assessment Tests and assessments shall be carried out under reasonably foreseeable fault conditions In some complex systems e g where the optical output is dependent on the integrity of other components and the performance of circuit design and software it may be necessary to use other recognised methods for hazard safety assessment see Annex C 11 IS 14624 Part 2 2012 IEC 60825 2 2005 However faults which result in the emission of radiation in excess of the hazard level need not be considered if they are for a limited duration only and it is not reasonably foreseeable that human access to the radiation will occur before the product is taken out of service 4 9 Hazard level requirements by location type The required hazard level shall be determined for each accessible location within an OFCS NOTE 1 This includes access to optical fibres that can become broken NOTE 2 This standard is applicable for the operation and maintenance of OFCS For the safety of the user hazard level 4 is not a
10. controlled areas it could be higher 13 IS 14624 Part 2 2012 IEC 60825 2 2005 Annex B informative Summary of requirements at locations in OFCS Hazard level Location type Unrestricted Restricted Controlled 1 No requirements No requirements No requirements 1M Class 1 from connectors No labelling or marking No requirements that can be opened by an required if connectors that end user 1 can be opened by end user are Class 1 If output is Class 1M then labelling or No labelling or marking marking is required 2 requirement 2 2 Labelling or marking 2 Labelling or marking 2 Labelling or marking 2 2M Labelling or marking 2 Labelling or marking 2 Labelling or marking 2 and Class 2 from connector 1 3R Not permitted 3 4 Labelling or marking 2 and Labelling or marking 2 Class 1M from connector 1 3B Not permitted 3 4 Not permitted 3 4 Labelling or marking 2 and Class 1M or 2M from connector 1 4 Not permitted 3 4 Not permitted 3 4 Not permitted 3 4 NOTE 1 Where the information contained in this annex differs from the requirements contained in Clause 4 the requirements of Clause 4 have precedence NOTE 2 Reference to Class X in the table above means access to radiation that is within the accessible emission limits corresponding to Class X as given in IEC 60825 1 1 See 4 4 2 See 4 6 1 3 See 4 5 and 4 8 2 Where systems emplo
11. from bundles of broken i e not cleaved fibre within a broken fibre cable does not increase beyond that of the worst case fibre within that cable This has been shown by a considerable number of measurements on broken fibre ends consideration of reflection and scattering at fibre ends and random alignment and movement of fibre ends These measurements and considerations have also been shown to apply to broken ribbon fibre but not to ribbon fibre cleaved as a unit see D 4 5 D 4 5 Ribbon cable Ribbon fibre ends cleaved as a unit may exhibit a higher hazard level than that of a single fibre An example would be eight fibres within a ribbon each carrying a power level just within hazard level 1M Individually they are of a relatively safe 1M hazard level but cleaved as an unseparated unit the hazard level might become 3B thus presenting a genuine eye risk This results from the small centre centre separation distances of typical ribbon fibre of 150 um to 250 um The low angular separation of several equally spaced fibres leads to a cumulative effect At the measurement distance of 100 mm the a of one single mode fibre is lt amp min for cw emission Qin 1 5 mrad see 8 4 c of IEC 60825 1 The angular subtense of the ribbon in its plane will depend on the number of fibres and their separation for example an eight fibre ribbon with fibres spaced at 200 um will subtend 14 mrad at 100 mm This subtense exceeds Q min and the ribbon is
12. is the wavelength m 40 IS 14624 Part 2 2012 IEC 60825 2 2005 Table D 14 Examples of power limits for OFCS having automatic power reduction to reduce emissions to a lower hazard level Wavelength Fibre mode Maximum Maximum Maximum Shutdown Measurement field power output power output power output times distance diameter unrestricted restricted controlled nm um mW mW mW s m 1310 1310 1310 1 0 1 0 1 1 500 1 500 1 400 1 1774 1 500 1 550 0 1 0 1 0 25 NOTE The fibre parameters used are the most conservative case Listed figures for 2 1 310 nm 1 550 nm are calculated for a fibre of 11 microns mode field diameter MFD and those for 4 980 nm are for 7 um MFD Many systems operating at 1550nm with the use of erbium doped fibre amplifiers EDFAs pumped by 1 480 nm or 980 nm lasers use transmission fibres with smaller MFDs For example 1 550 nm dispersion shifted fibre cables have upper limit values of MFD of 9 1 um In this case the maximum power outputs for unrestricted and restricted areas at 1480 nm and 1550 nm are 1 44 times the values in Table D 14 and those for controlled areas at 1 480 nm and 1 550 nm are 1 46 times the values in Table D 14 41 IS 14624 Part 2 2012 IEC 60825 2 2005 Annex E informative Guidance for service and maintenance E 1 Tests and measurements E 1 1 Tests measurements and operations in cable ducts and switching centres should be con
13. kauributanol value of 29 an initial boiling point of approximately 65 C a dry point of approximately 69 C and a mass per unit volume of approximately 0 7 kg l NOTE The above requirement and test is identical to that contained in 1 7 13 of IEC 60950 1 13 2 4 7 Organizational requirements 4 7 1 Manufacturers of ready to use OFCS turn key systems or subassemblies Manufacturers of OFCS turnkey end to end systems or subassemblies shall 1 ensure that the equipment satisfies the applicable requirements of this standard 2 provide the following information a adequate description of the engineering design features incorporated into the product to prevent exposure to radiation above the MPE levels b adequate instructions for proper assembly maintenance and safe use including clear warnings concerning precautions to avoid possible exposure to radiation above the MPE levels 2 Figures in square brackets refer to the Bibliography IS 14624 Part 2 2012 IEC 60825 2 2005 c adequate instructions to installation organizations and service organizations to ensure the product can be installed and serviced in a manner that the radiation accessible under reasonably foreseeable events meets the requirements of Clause 4 d the hazard levels at accessible locations within the system or subassembly and the parameters upon which those hazard levels are based e for systems with APR the reaction time and operating parameters of
14. the APR where installation or service requires overriding an APR information shall be included to enable the operating organization to specify safe work practices while the APR is overridden and safe procedures reinstating and testing such systems if a manual initiated restart temporarily inactivates the APR the timing of the restart shall be stated clearly in the user manual all scenarios e g removal or failure of a controller or other element where the APR would not be operable including appropriate precautions that need to be taken under such conditions f any other information relevant to the safe use of the OFCS g a statement that the equipment must be installed according to the manufacturer s instructions including the warning CAUTION Use of controls or adjustments or performance of procedures other than those specified herein may result in hazardous radiation exposure 4 7 2 Installation and service organization The organization responsible for the installation and servicing of OFCS shall follow the manufacturer s instructions for installation of equipment in a manner that will ensure that the accessible radiation under reasonably foreseeable events satisfies the requirements of Clause 4 Before placing an OFCS into service the installation organization or service organization as applicable shall ensure that APR if used is in appropriate working condition as designated in 4 5 and 4 8 For system
15. within the wavelength range 400 nm to 700 nm or Class 1 in all other cases then suitable means shall limit access to the radiation from the connector NOTE In an unrestricted location the highest hazard levels permitted are hazard level 2M for the wavelength range 400 nm to 700 nm and hazard level 1M in all other cases see 4 9 1 4 4 2 Restricted locations In restricted locations if the radiation level exceeds the accessible emission limits of Class 2M within the wavelength range 400 nm to 700 nm or Class 1M in all other cases then suitable means shall limit access to the radiation from the connector NOTE Ina restricted location the highest hazard level permitted is hazard level 1M 2M or 3R whichever is higher see 4 9 2 IS 14624 Part 2 2012 IEC 60825 2 2005 4 4 3 Controlled locations In controlled locations if the radiation level exceeds the accessible emission limits of Class 2M within the wavelength range 400 nm to 700 nm or Class 1M in all other cases then suitable means shall limit access to the radiation from the connector NOTE In a controlled location the highest hazard level permitted is hazard level 3B see 4 9 3 4 5 Automatic power reduction APR and restart pulses If equipment makes use of an automatic power reduction APR system in order to reduce its assigned hazard level then it shall be restarted with restrictions which are described in the following three scena
16. 1 notes to Tables 1 to 4 and T lt t 100 s see above Prev 3 9 x 10 4C4C7 W where C4 100 002 A 700 for 840 nm and 870 nm C 5 for wavelengths gt 1 050 nm 20 IS 14624 Part 2 2012 IEC 60825 2 2005 and C7 1 for 840 nm and 870 nm C7 8 for wavelengths gt 1 050 nm hence AELggonm 0 74 mW AELg70nm 0 85 mW AEL1 300 nm 15 6 mW The measurement specifications given in 9 3 of IEC 60825 1 require the most restrictive condition in Table 10 of IEC 60825 1 to be applied For a divergent beam from an optical fibre the most restrictive condition is 2 Using Table 10 the aperture diameter is 7 mm and the measuring distance is 14 mm for thermal limits Using the expression for the diameter of the beam from an optical fibre equation 1 in A 6 of IEC 60825 1 the diameter at the 63 1 e points for the smallest NA fibre worst case is Go Ne a Gai Thus in this case all of the fibre power would be collected by the 7 mm aperture and no correction is needed Summing the ratios of the power at each wavelength to the corresponding AEL yields 0 45 3 Power _ 0 16 T 0 16 E 4x0 16 _ AEL 0 74 0 85 15 6 This ratio is less than 1 thus the accessible emission is within Class 1 limits and so hazard level 1 applies at that location D 4 2 Bi directional full duplex transmission There is no additive effect from each separate direction of transmission as each broken fibre cable end represents a separ
17. 7 Ce 1 1 2 1 9 2 5 3 2 3 9 4 5 5 2 i 10 10 07 10 31 10 55 10 8 11 06 11 32 11 59 AEL mW 15 6 18 7 28 9 39 49 58 8 68 6 78 2 Di ai 15 6 9 3 9 6 9 75 9 8 9 8 9 8 9 8 Solution for b At 1 550 nm the hazard for the cornea dominates Consequently there is no correction factor C6 The maximum power per fibre is simply the corresponding AEL for one source divided by the number of fibres i e 10 mW 8 1 25 mW D 4 5 2 Ribbon fibre issues The additive property of the radiation hazard from ribbon fibre sources therefore means that the hazard level of a location can depend on the choice of cable type For instance it is impractical to switch off essential systems if they are designed for live maintenance and if the resulting hazard level at the location is not compatible with the location type A solution will be required to reduce the hazard if ribbon fibres are to be used in this fibre network The solution may not be too difficult As broken ribbon fibres do not present a problem it is only the cleaving and splicing operations that require consideration Separated ribbon being no different from normal fibre also does not present a problem If access to unseparated cleaved fibre end can be assuredly prevented then as the hazard level relates to accessible emission limits the hazard level may be prevented from increasing Any method would have to prevent access under reasonably foreseeable circumstances i e not just an instruction no
18. ERABAD JAIPUR KANPUR LUCKNOW NAGPUR PARWANOO PATNA PUNE RAJKOT THIRUVANATHAPURAM VISAKHAPATNAM Published by BIS New Delhi
19. OOO kkk kok kkk Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities in order to promote transparency and accountability in the working of every public authority and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public particularly disadvantaged communities and those engaged in the pursuit of education and knowledge the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public Tat AT afar st aT afar Tad Hl Sls AL h Ah Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru The Right to Information The Right to Live Step Out From the Old to the New iom4G24 2 2012 Safety of laser products Part 2 Samemy of Optical Fibre Communication Systems OFCS LITD 11 Fibre Optics Fibers Cables and Devices Satyanarayan Gangaram Pitroda Bhartrhari Nitisatakam kk kkk kk kk kkk kk kk BLANK PAGE PROTECTED BY COPYRIGHT IS 14624 Part 2 2012 IEC 60825 2 2005 IRA Wah cis STS Hl GAM aM 2 ua wget Gat wefa at Grant wonferat ARTE Yee FRI Indian Standard SAFETY OF LASER PRODUCTS PART 2 SAFETY OF OPTICAL FIBRE COMMUNICATION SYSTEMS OFCS First Revision IC
20. S 31 260 33 180 01 BIS 2012 BUREAU OF INDIAN STANDARDS MANAK BHAVAN 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 August 2012 Price Group 14 Fibre Optics Fibres Cables and Devices Sectional Committee LITD 11 NATIONAL FOREWORD This Indian Standard Part 2 First Revision which is identical with IEC 60825 2 2005 Safety of laser products Part 2 Safety of optical fibre communication systems OFCS issued by the International Electrotechnical Commission IEC was adopted by the Bureau of Indian Standards on the recommendation of the Fibre Optics Fibres Cables and Devices Sectional Committee and approval of the Electronics and Information Technology Division Council This standard was originally published in 1998 which was identical to IEC 825 2 1996 and has now been revised to align it with the latest version of IEC 60825 2 2005 The text of IEC Standard has been approved as suitable for publication as an Indian Standard without deviations Certain conventions are however not identical to those used in Indian Standards Attention is particularly drawn to the following a Wherever the words International Standard appear referring to this standard they should be read as Indian Standard b Comma has been used as a decimal marker while in Indian Standards the current practice is to use a point as the decimal marker The technical committee has reviewed the provision of the following Interna
21. a modulator and threshold bias generator Include automatic power reduction APR circuits in the analysis if the function of the APR is to achieve the intended classification or if an APR component failure could cause a significant increase in the accessible power 28 IS 14624 Part 2 2012 IEC 60825 2 2005 D 5 5 1 2 Step 2 identify component failure modes Construct a table listing the components their circuit identifier and their most likely failure modes as shown in Table D 3 below Table D 3 Identification of components and failure modes example Uncooled laser Increase in output Decrease in output No output TR1 BFR 96 Mullard Short circuit lt 500 mW NPN Open circuit R1 47R2 Short circuit 0 25 W Open circuit Parameter drift Short circuit Open circuit Parameter drift 0 47 uF 10 Short circuit 50 V Open circuit Parameter drift The US Department of Defense Reliability Analysis Center RAC publication 2 gives a list of likely failure modes Include a column for comments and Ae an explanation of the likely outcome of the failure from the engineers consulted see step 3 D 5 5 1 3 Step 3 determine beta values Circuit designers or repair engineers are the best people to consult for this task since it requires a knowledge of how each component operates in the circuit Beta values depend on the criticality of the failure mode A simple analysis assigns a probability figure to the beta value by consi
22. ate hazard if the fibre breaks The hazard level is determined by the transmission direction with the higher power D 4 3 Automatic power reduction By using automatic power reduction in an end to end OFCS it is possible to assign a lower hazard level than would otherwise have been the case This is important when the hazard level of the internal optical transmitters amplifiers of a system may put a limitation on where that system may be deployed See Annex B Automatic power reduction should not take the place of good working practices and proper servicing and maintenance Also the reliability of the APR mechanism should be taken into account when assessing the hazard level 21 IS 14624 Part 2 2012 IEC 60825 2 2005 Assessment of the hazard level should take place at the time of reasonably foreseeable human access to radiation for example after a fibre break unless measurement at a later time would result in a larger exposure see 4 8 1 and 4 8 2 Automatic power reduction cannot be regarded as a universally protective measure because after a fibre break it is common practice to use an optical test set usually an optical time domain reflectometer OTDR to determine the location of the break This instrument launches laser power down the fibre under test Therefore even if the normal telecommunications transmitter is shut down or removed the diagnostic instrument could at a later time apply laser power to the fibre These
23. bassemblies that generate or amplify optical radiation are critical to the safety of the OFCS and because they have to meet part of the requirements these items are also included within the scope of this standard The manufacturers of individual passive components or passive subassemblies that are not yet incorporated into the end to end system can not know the associated hazard level and so these items are excluded from the scope of this standard This standard does not address safety issues associated with explosion or fire with respect to OFCS deployed in hazardous locations D 2 Areas of application D 2 1 Typical OFCS installations a Locations with controlled access see 3 13 cable ducts street cabinets dedicated and delimited areas of distribution centres test rooms in cable ships NOTE Where service access to cable ducts and street cabinets could expose the general public to radiation in excess of the accessible emission limit of Class 1 appropriate temporary exclusion provisions e g a hut should be provided IS 14624 Part 2 2012 IEC 60825 2 2005 b Locations with restricted access see 3 14 secured areas within industrial premises not open to the public secured areas within business commercial premises not open to the public for example telephone PABX rooms computer system rooms etc general areas within switching centres delimited areas not open to the public on train
24. bles described in IEC 60825 1 The assessment of hazard level is described in 4 8 1 The assessment can be an actual measurement or be based upon calculation of emitting powers and known time constants Annex A of this standard gives the following additional clarification A whole OFCS will not be classified in the same way as required by IEC 60825 1 This is because under intended operation the optical radiation is totally enclosed and it can be argued that a rigorous interpretation of IEC 60825 1 would give a Class 1 allocation to all systems which may not reflect the potential hazard accurately Based upon this statement a complete OFCS can be regarded as a Class 1 laser product because under normal conditions the emissions are completely enclosed like a laser printer and no light should be emitting outside the protective housing It is not until the fibre becomes broken or an optical connector is unplugged that someone might be exposed to a level of optical radiation which is potentially hazardous if the internal emitters or amplifier outputs are of high enough power Therefore for each optical output port the hazard level must be assessed The hazard level limits are dependent on the dominant wavelength range taking into consideration that IEC 60825 1 defines different limits for different wavelength ranges Details can be found in IEC 60825 1 Furthermore this standard allows the use of automatic power reduction APR tech
25. cation according to IEC 60825 1 It applies to the complete installed end to end OFCS including its components and subassemblies that generate or amplify optical radiation Individual components and subassemblies that are sold only to OEM vendors for incorporation into a complete installed end to end OFCS need not be assessed to this standard since the final OFCS should itself be assessed according to this standard NOTE The above statement is not intended to prevent manufacturers of such components and subassemblies from using this standard if they wish to do so or are required to do so by contract This standard does not apply to optical fibre systems primarily designed to transmit optical power for applications such as material processing or medical treatment In addition to the hazards resulting from laser radiation OFCS may also give rise to other hazards such as fire This standard does not address safety issues associated with explosion or fire with respect to OFCS deployed in explosive atmospheres Throughout this part of IEC 60825 a reference to laser is taken to include light emitting diodes LEDs and optical amplifiers The objective of this Part 2 of IEC 60825 is to protect people from optical radiation resulting from OFCS provide requirements for manufacturers installation organizations service organizations and operating organizations in order to establish procedures and supply information so that prope
26. closed under intended operation However because of the extended nature of these systems where optical power under certain conditions may be accessible many kilometres from the optical source the precautions to minimise the hazard will be different from those concerning laser sources which are normally under local operator control It should be noted that many OFCS contain LEDs which are included in the scope of IEC 60825 1 The potential hazard of an OFCS depends on the likelihood of the protective housing being breached e g a disconnected fibre connector or a broken cable and on the nature of the optical radiation that might subsequently become accessible The engineering requirements and user precautions that are required to minimise the hazard are specified in this Part 2 of IEC 60825 Each accessible location within an OFCS is allocated by the system operating organization or its delegate a hazard level that gives a guide as to the potential hazard if optical radiation becomes accessible These hazard levels are described as hazard levels 1 to 4 in a fashion similar to the classification procedure described in IEC 60825 1 In fibre optic applications the limits of hazard levels 1M and 2M are often higher than the limit of hazard level 3R but less than the limit of hazard level 3B For these applications hazard level 3R is not applicable see notes to 3 6 3 8 and 3 9 Where operating organizations subcontract the installation ope
27. considered as an intermediate extended source and the point source AEL may be increased by factor Cg Any angular dimension that is more than amp max Q max 100 mrad or less than pin 1 5 mrad should be limited to Q max OF Ain respectively before determining the mean The total power permitted in the ribbon fibre is determined by the worst case combination of any individual fibres for details see IEC 60825 1 classification rules for non circular and multiple sources 24 IS 14624 Part 2 2012 IEC 60825 2 2005 D 4 5 1 Ribbon fibre example calculation The ribbon consists of eight equally spaced by 200 um single mode fibres What is the maximum allowed Class 1 cw output power per fibre for a wavelength of a 1 310 nm and b 1 550 nm Solution for a Evaluations should be made for every single fibre or assembly of fibres necessary to assure that the source does not exceed the AEL for each possible angle a subtended by each partial area where QAmin lt amp lt Omax Table D 2 below shows the AEL per combination of fibres as well as the resulting maximum permitted power within one single fibre of the combination The combination of two fibres represents the worst case Therefore the maximum power for one single fibre of the ribbon is 9 3 mW Table D 2 Relation between the number of fibres in a ribbon fibre and the maximum permitted power example emman Ty 2 a s e
28. d E 1 5 The operating organization should establish work practices preventing human exposure to radiation in excess of the relevant MPE E 2 Safety precautions E 2 1 General remarks E 2 1 1 In locations where during service or maintenance optical or laser radiation above the MPE levels may be encountered e g during switching in controlled locations appropriate eye protection should be provided 42 IS 14624 Part 2 2012 IEC 60825 2 2005 E 2 1 2 Before working on any optical fibre cable or system the end user should check the hazard level at accessible locations In the case of systems that are installed and activated the hazard level should be identified at accessible locations by warning labels Precautions appropriate to the hazard level should be taken on systems that are known to be or could become operational During installation hazard level labels may not have been provided yet and in their absence precautions appropriate to the classification of any transmitters or test equipment containing optical sources connected to the fibre should be used E 2 1 3 During the installation or testing of an optical fibre cable or network it is recommended that only test equipment having an output designated hazard level 1 1M 2 or 2M per IEC 60825 2 or Class 1 1M 2 or 2M per IEC 60825 1 be used For optical fibre communications systems located in a restricted location or a controlled location it is possible to use test eq
29. d 0 18 numerical aperture multimode MM fibres core diameter lt 150 um Hazard level Wavelength and fibre type 633 nm MM 780 nm MM 850 nm MM 980 nm MM 980 nm SM 1310 nm MM 1 310 nm SM 1400 nm 1 600 nm MM 1 420 nm SM 1 550 nm SM 0 39 mw 4 1 dBm 0 57 mW 2 5 dBm 0 78 mw 1 1 dBm 1 42 mW 1 53 dBm 1 42 mW 1 53 dBm 15 6 mW 12 dBm 15 6 mW 12 dBm 10 mW 10 dBm 10 mW 10 dBm 10 mW 10 dBm 3 9 mW 5 9 dBm 5 6 mW 7 5 dBm 7 8 mW 8 9 dBm 14 1 mW 11 5 dBm 2 66 mW 4 2 dBm 156 mW 21 9 dBm 42 8 mW 16 3 dBm 384 mW 25 8 dBm 115 mW 20 6 dBm 136 mW 21 3 dBm 1 mW 0 dBm 10 mW 10 dBm See note to 3 9 500 mW 27 dBm See note to 3 9 500 mW 27 dBm See note to 3 9 500 mW 27 dBm See note to 3 9 500 mW 27 dBm 500 mW 7 26 mW 8 6 dBm 27 dBm See note to 3 9 500 mW 27 dBm 80 mW 500 mW 19 dBm 27 dBm See note to 3 9 500 mW 27 dBm See note to 3 9 500 mW 27 dBm See note to 3 9 500 mW 27 dBm 18 IS 14624 Part 2 2012 IEC 60825 2 2005 NOTE 1 Hazard Levels 1M and 2M The maximum power shown in the table for 11 microns fibre is limited by the power density The precise fibre power limit is therefore determined by the minimum expected beam divergence which is in turn dependent on the single mode fibre mode fiel
30. d diameter MFD This may change for different values of the MFD and there are significant changes in Class limits as the MFD changes Some high power connectors use enlarged mode field diameter MFD and the far field divergence is lower These connectors can result in a higher hazard level and determination of the hazard level when using these connectors is strongly recommended NOTE 2 1310 nm figures The 1 310 nm figures are calculated for 1 270 nm which is the shortest wavelength in the 1 310 nm telecommunications window NOTE 3 Fibre parameters The fibre parameters used are the most conservative cases single mode figures are calculated for a fibre of 11 microns mode field diameter and multimode figures for a fibre with a numerical aperture of 0 18 Many systems operating at 980 nm and 1 550 nm use fibres with smaller MFDs For example the limit for hazard level 1M when a wavelength of 1 550 nm is transmitted along dispersion shifted fibre cables having upper limit values of MFD of 9 1 um is 197 mW For other MFD values and wavelengths please refer to IEC 60825 1 example A 6 3 NOTE 4 Hazard level 1M limits for lt 1 310 nm The hazard level 1M limits for single mode fibres at 900 nm and below are not presented here as the divergence that these wavelengths will undergo is rather variable This is because these wavelengths are in fact multimoded in standard 1 310 nm single mode fibre and the exact divergence will depend on the rathe
31. dering just three categories as illustrated in Table D 4 Table D 4 Beta values example Does the failure mode cause the laser Beta value power to exceed Class 1M AEL The consulted engineers may be able to give better estimates for the beta values It is good practice to simulate fault conditions whenever possible 29 IS 14624 Part 2 2012 IEC 60825 2 2005 D 5 5 1 4 Step 4 determine failure rates The next step is to determine base failure rates for each component and apportion failure rates to failure modes This information can be obtained from e g the following sources data obtained by the analysis of in service failures BT Handbook of Reliability Data HRD5 3 provides intrinsic failure rates for generic component types at the upper 60 confidence limit RAC publication 2 lists the apportionment of failure rates to failure modes Mil HDBK 217 17 and RAC publication NPRD 14 For example HRD5 lists the base failure rate Abase for a silicon small signal bipolar transistor as eight FITs and the RAC publication lists the apportionment of failure modes a as 73 for short circuits and 27 for open circuits Insert the values into the appropriate columns in the spreadsheet Determine the system failure rate by multiplying the columns horizontally and then add vertically The overall failure rate represents the probability of the system exceeding the intended classificatio
32. e location within an OFCS at which under a reasonably foreseeable event human access to laser radiation in excess of the accessible emission limits of Class 2 for the applicable wavelengths and emission duration will not occur NOTE If the applicable limit of hazard level 1M is larger than the limit of 2 and less than the limit of 3B hazard level 1M is allocated 3 8 hazard level 2M hazard level 2M is assigned to any accessible location within an OFCS at which under a reasonably foreseeable event human access to laser radiation in excess of the accessible emission limits of Class 2 for the applicable wavelengths and emission duration will not occur whereby the level of radiation is measured with the measurement conditions for Class 2M laser products see IEC 60825 1 NOTE If the applicable limit of hazard level 2M is larger than the limit of 3R and less than the limit of 3B hazard level 2M is allocated 3 9 hazard level 3R hazard level 3R is assigned to any accessible location within an OFCS at which under a reasonably foreseeable event human access to laser radiation in excess of the accessible emission limits of Class 3R for the applicable wavelengths and emission duration will not occur NOTE If the applicable limit of hazard level 1M or 2M is larger than the limit of 3R and less than the limit of 3B hazard level 1M or 2M is allocated IS 14624 Part 2 2012 IEC 60825 2 2005 3 10 hazard level 3B hazard level 3B is a
33. enced document including any amendments applies IEC 60825 1 Safety of laser products Part 1 Equipment classification requirements and user s guide Amendment 1 1997 Amendment 2 2001 3 Terms and definitions For the purposes of this document the terms and definitions contained in IEC 60825 1 as well as the following terms and definitions apply 3 1 accessible location any part or location within an OFCS at which under reasonably foreseeable events human access to laser radiation is possible without the use of a tool 3 2 automatic power reduction APR a feature of an OFCS by which the accessible power is reduced to a specified level within a specified time whenever there is an event which could result in human exposure to radiation e g a fibre cable break NOTE The term automatic power reduction APR used in this standard encompasses the following terms used in recommendations of the International Telecommunication Union ITU automatic laser shutdown ALS automatic power reduction APR automatic power shutdown APSD 3 3 end user person or organization using the OFCS in the manner the system was designed to be used NOTE 1 The end user cannot necessarily control the power generated and transmitted within the system 1 A consolidated edition 1 2 exists including IEC 60825 1 1993 and its Amendment 1 1997 and Amendment 2 2001 IS 14624 Part 2 2012 IEC 60825 2 2005
34. g to the previous paragraph and with any additional local instructions and circumstances have a responsible attitude to safety Nominated persons should be appointed by line management and be notified of their appointment A list of nominated persons at each installation should be recorded and prominently displayed Before starting work the person authorized to carry out the work the originator should contact a nominated person at the appropriate optical power source and request that the power on the relevant fibres be switched off on duplex systems a nominated person should be contacted at each end on being informed that the power has been switched off complete the necessary forms which should be retained by the originator These forms need not be completed if the originator and the nominated person are one and the same verify with an energized live fibre identifier or optical power meter that the power is off on completion of the work inform a nominated person at the appropriate optical power source s 39 IS 14624 Part 2 2012 IEC 60825 2 2005 e On receipt of a request from an originator to switch off an optical power source the nominated person should D 7 record the time and date of the request and the details of the originator Forms should be kept on file at the location of the optical source switch off the appropriate power source with key control if fitted co
35. highest of the levels arising from each of those systems Based on the hazard level determined appropriate actions shall be taken to ensure compliance with this standard These actions could for example involve restriction of access to the location or the implementation of safety features or redesign of the optical communications system to reduce the hazard level Suppliers of active components and subassemblies in conformance with this standard that do not comprise an OFCS need to comply only with the applicable portions of Clause 4 OFCS that also transmit electrical power shall meet the requirements of this standard in addition to any applicable electrical standard NOTE When determining the hazard level two characteristics have to be taken into account IS 14624 Part 2 2012 IEC 60825 2 2005 1 What is the maximum permissible exposure MPE The level of exposure must be determined at a location where it is reasonably foreseeable that a person could be exposed to radiation coming from the OFCS The time taken for the APR system if present to operate must be included when determining the MPE If the OFCS does not incorporate APR then meeting the requirements referred to in Note 2 below will be taken as automatically meeting the requirements of this Note 1 without further investigation or tests Requirements are described in 4 8 2 2 What is the maximum permitted power at which the OFCS can operate after a reasonable foreseeable even
36. iability data 1995 NPRD 95 Reliability Analysis Center US Dept of Defense 1995 Prepared by Reliability Analysis Center PO Box 4700 Rome NY ITU T Recommendation G 664 Optical safety procedures and requirements for optical transport systems IEC 60825 12 Safety of laser products Part 12 Safety of free space optical communication systems used for transmission of information MIL HDBK 217F Reliability Prediction Of Electronic Equipment COCHRANE P and HEATLEY DJT Reliability Aspects of Optical Fibre Systems amp Networks BTTJ Special Issue on Future Telecommunication Systems amp Networks No 2 April 1994 Vol 12 pp 77 92 also found at http innovate bt com people heatledj papers reliability reliability 47 Bureau of Indian Standards BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promote harmonious development of the activities of standardization marking and quality certification of goods and attending to connected matters in the country Copyright BIS has the copyright of all its publications No part of these publications may be reproduced in any form without the prior permission in writing of BIS This does not preclude the free use in course of imple menting the standard of necessary details such as symbols and sizes type or grade designations Enquiries relating to copyright be addressed to the Director Publications BIS Review of Indian Standards
37. iers have the capability to generate significant levels of optical power Powers of the order of gt 500 mW are not uncommon This may result in a potential hazard without the use of protection mechanisms For this reason it is important that a suitable means is employed for limiting such power levels when amplifiers are accessed for repair or maintenance Consideration of appropriate mechanisms including but not limited to APR to reduce the hazard level and the use of shuttered connectors may be necessary 22 IS 14624 Part 2 2012 IEC 60825 2 2005 D 4 3 2 APR for distributed optical amplification systems APR for distributed optical amplification systems e g Raman is required not only on main signal sources but also on pump lasers The response of such a distributed optical amplification system could have shorter time periods than other lower power systems depending on the actual pump power in the Raman amplification system of interest D 4 3 3 Fibre in a splice tray As powers increase in an OFCS it is important that splicing operations on potentially energized fibres of hazard level 3B take into consideration the safety of the operator and a fully enclosed splicing system should be employed in such cases If splicing is not to take place in a protective enclosure automatic power reduction is an option for reducing the hazard level and therefore the exposure D 4 3 4 Connectorised systems Another occurrence where access
38. istrative control is present to make it inaccessible except to authorized personnel with appropriate laser safety training NOTE For examples see D 2 1 a 3 14 location with restricted access restricted location an accessible location that is normally inaccessible by the general public by means of any administrative or engineering control measure but that is accessible to authorized personnel who may not have laser safety training NOTE For examples see D 2 1 b 3 15 location with unrestricted access unrestricted location an accessible location where there are no measures restricting access to members of the general public NOTE For examples see D 2 1 c 3 16 manufacturer organization or individual that assembles optical devices and other components in order to construct or modify an OFCS 3 17 operating organization organization or individual that is responsible for the operation of an OFCS IS 14624 Part 2 2012 IEC 60825 2 2005 3 18 optical fibre communication system OFCS an engineered end to end assembly for the generation transfer and reception of optical radiation arising from lasers LEDs or optical amplifiers in which the transference is by means of optical fibre for communication and or control purposes 3 19 reasonably foreseeable event an event the occurrence of which under given circumstances can be predicted fairly accurately and the occurrence probability or frequency of which is not low or
39. itiated manually and the continuity of the communications path is not assured the timing and power of the restart process shall be restricted such that the hazard level assigned to each accessible location of the system shall not be exceeded 4 5 4 Disabling of the APR If a manual initiated restart of the system temporarily inactivates the APR the system must indicate that the APR is not operable for the duration of the reboot so that the operating organization can take the appropriate precautions Unless these conditions are met the hazard level must be assigned using the transmitting power level before APR IS 14624 Part 2 2012 IEC 60825 2 2005 Disabling of the APR mechanism shall not be permitted for Class 3B and 4 transmitting powers unless all of the following conditions are met 1 that such disabling is necessary only for the infrequent incidences of system installation and service 2 that such disabling can only be done via software commands or a manual lockout key system 3 if disabling is done via software commands incorporated in such software shall be a security system that prevents inadvertent disabling of the APR mechanism 4 that such software incorporate a warning indicator that the APR will be disabled if the procedure is continued 5 continuous operation of the traffic carrying OFCS with APR disabled shall be prevented by suitable engineering means 6 proper instructions on the safe use of the equipme
40. l radiation 38 IS 14624 Part 2 2012 IEC 60825 2 2005 If working on energized systems in locations with hazard level 3B is not permitted as described above then the following working practices should be used all general practices defined in D 6 1 the equipment generating the optical radiation should be de energized thereby de energizing the OFCS as detailed in D 6 4 check that there is no optical power in the fibre by using an approved optical power meter capable of withstanding the highest power transmitted in the system without damage cover the ends of all exposed fibres not being worked on Always ensure unmated connectors are appropriately attenuated using the in built connector shutter mechanism or an end cap use only indirect viewing aids for example televised or shadow imaging splicing machines Do not use microscopes or eye loupes without authorization when using optical test cords the optical power source should be the last to be connected and the first to be disconnected D 6 4 Formal power down and power up procedure for hazard level 3B When de energizing an OFCS if working on energized systems is not permitted the following procedure should be adopted a A nominated person at an optical power source should have been trained to an appropriate level on the type of equipment which has to be switched on and off be conversant with the instructions and safety requirements relatin
41. le of a standards based approach that can be used to quantify the reliability of automatic power reduction APR safety systems In the scheme specified by IEC 61508 1 requirements for a safety related control system are categorised into one of four safety integrity levels SIL Depending on the SIL different requirements apply According to IEC 61508 1 hardware random failures and systematic failures have to be taken into account Hardware random failures can be calculated using reliability data Systematic failures take into account the possibility of design failures failures due to environmental stress or influence and operational failures NOTE 1 The following is the SIL definition from IEC 61508 1 Discrete level one out of possible four for specifying the safety integrity requirements of the safety functions to be allocated to the electrical electronic programmable electronic safety related systems where safety integrity level 4 has the highest level of the safety integrity and safety integrity level 1 has the lowest NOTE 2 Where programmable electronic devices are used to control hazard levels it is recommended that the IEC 61508 series of standards should be applied If the system is purely hardware it can be analysed using familiar techniques such as FMECA The standard provides several example methods how an application sector like OFCS could determine a recommended safety integrity level for specified product haza
42. lerance and the safe failure fraction should be taken into account according to IEC 61508 2 The SILs are presented as two sets of number ranges one set for high demand mode and one set for low demand mode for the safety device After installation optical fibre systems are seldom disturbed in any fashion that would unintentionally break or open the optical path Therefore there would be a very infrequent need for the automatic power reduction APR system to shut down or reduce the optical power In the terminology of the IEC 61508 series the APR would operate in a low demand mode see definitions in Table D 10 below NOTE For example mean time between failures for optical fibre cables have been determined to be in the range of 2 years to greater than 160 years See Tables 1 and 2 in Cochrane and Heatley 18 Table D 10 Modes of operation Definitions from IEC 61508 4 3 5 12 Term Definition Mode of operation Way in which a safety related system is intended to be used with respect to the frequency of demands made upon it which may be either Low demand mode where the frequency of demands for operation made on a safety related system is no greater than one per year and no greater than twice the proof test frequency or High demand or continuous where the frequency of demands for operation made on a safety related system is mode greater than one per year or greater than twice the proof check frequency NOTE 1
43. level 4 as specified in this standard Manual shutdown of the system under repair maintenance service conditions is currently the practice for many operators because of the hazardous electrical power associated with the submerged cable This electrical power is used to power the undersea repeaters along the route In the future for repeaterless systems this electrical power may no longer be a part of the cable However the work practice to de energize fibre before extraction should be continued and maintained because of the hazards of the associated optical power 23 IS 14624 Part 2 2012 IEC 60825 2 2005 D 4 3 6 APR for restricted and unrestricted locations OFCS designers need to be aware of the restrictions in 4 9 regarding restricted and unrestricted locations For these locations the designers should consider the incorporation of APR into any system that has the potential to expose humans to optical power of Class 3B or above Appropriate break detection and reliability precautions should be taken when designing this power down system D 4 3 7 APR for ribbon cables The use of ribbon cables can place the OFCS in a more restrictive hazard level A careful hazard assessment as explained in D 4 5 should take place and appropriate APR shuttering and splicing considerations should be evaluated and implemented with respect to the potentially increased hazard level and the location of the OFCS D 4 4 Multiple fibres The hazard
44. llowed throughout the standard Where systems employ normal transmitting power levels exceeding the acceptable hazard level for the particular location type protection systems such as automatic power reduction may be used to determine the actual hazard level 4 9 1 Unrestricted access locations At a location with unrestricted access the hazard level shall be 1 1M 2 or 2M NOTE If the applicable limit of hazard level 1M is larger than the limit of 2 and less than the limit of 3B hazard level 1M is allocated 4 9 2 Restricted access locations At a location with restricted access the hazard level shall be 1 1M 2 2M or 3R NOTE 1 If the applicable limit of hazard level 1M or 2M is larger than the limit of 3R and less than the limit of 3B hazard level 1M or 2M is allocated respectively NOTE 2 If the applicable limit of hazard level 1M is larger than the limit of 2 and less than the limit of 3B hazard level 1M is allocated 4 9 3 Controlled access locations At a location with controlled access the hazard level shall be 1 1M 2 2M 3R or 3B 12 IS 14624 Part 2 2012 IEC 60825 2 2005 Annex A informative Rationale The safety of laser products equipment classification requirements and user s guide are covered by IEC 60825 1 Part 1 is primarily aimed at self contained products which are under effective local control An OFCS will be safe under normal operating conditions because the optical radiation is totally en
45. mplete the warning label and affix it to the appropriate station equipment at the point of disconnection for example equipment rack distribution frame a label should be attached for each originator contact the originator and give him the job number and the time that the source was switched off on being informed that the work has been completed record the details appropriately and remove the warning label from the equipment before re energizing the source When more than one originator requires the same power source to be switched off the source should not be re energized before all work is completed Maximum output power during shutdown Table D 14 lists the maximum output power mW during the shutdown time for single mode OFCS which shut down to lower hazard level limits in 1 s for unrestricted locations and 3 s for restricted and controlled locations see 4 8 2 Engineering requirements as outlined in Annex B should be employed as appropriate to that lower hazard level The equation used to derive Table D 6 was NOHD 074 22A An alternative form of this equation is where P d MPE nd2MPE 1 x j 4t 2 1 ool 0125 mage ANOHD is the mode field diameter 1 e2 power density m is the total power in fibre W is the limiting aperture diameter m is the maximum permissible exposure Jm 2 NOHD is the nominal ocular hazard distance m t A is the shutdown time s
46. ms with a hazard level of 3B Such programmes should be directed by individuals competent in the field of laser and OFCS safety The programmes should provide as a minimum background information on OFCS safety information concerning the laser classification system and hazard levels 44 IS 14624 Part 2 2012 IEC 60825 2 2005 Annex F informative Clarification of the meaning of hazard level In this annex the difference between laser class defined in IEC 60825 1 and hazard level defined in IEC 60825 2 is further clarified F 1 Class The word class refers to a scheme by which based on emission levels a product or internal emitter can be grouped with respect to its safety These levels are described in the accessible emission limit tables in IEC 60825 1 Classes range from Class 1 which is safe under reasonably foreseeable conditions to Class 4 which is potentially the most hazardous case In IEC 60825 1 the classification of products is based on reasonably foreseeable operating conditions including single fault conditions F 2 Hazard level Hazard level is a term used in this standard which refers to the potential hazard from laser emissions at any location in an end to end fibre optic communication system that may be accessible during use or maintenance or in the event of a failure or fibre disconnection The assessment of the hazard level uses the class accessible emission limit ta
47. n This is illustrated in the following Table D 5 Table D 5 Determination of failure rates example ed bee Se Uncooled laser Increase in output 0 05 25 0 May result from fibre movement Decrease in output 0 65 No output 0 30 BFR 96 Mullard Short circuit 0 73 5 84 ae limited by R1 may still be safe lt 500 mW NPN Open circuit 0 27 see below 47R2 Short circuit 0 05 0 01 0 25 W Open circuit 0 84 Parameter drift 0 11 0 01 Chip failure 3K9 2 Short circuit 0 2 0 05 0 01 0 25 W Open circuit 0 0 2 0 84 0 Parameter drift 0 5 0 2 0 11 0 01 0 47 uF Short circuit 1 0 3 0 49 0 15 10 50 V Open circuit 0 0 3 0 29 Parameter drift 0 5 0 3 0 22 0 03 Overall failure rate 31 06 FITs S 06 FITs 30 IS 14624 Part 2 2012 IEC 60825 2 2005 In this example assuming 5 V power rail the maximum laser current is limited by R1 to about 35 mA This is unlikely to result in a 1 5 um laser exceeding the Class 1M limit In other cases this is not always applicable and reference should be made to the laser data sheet and individual component values In similar examples where a component failure is significant only if accompanied by simultaneous independent failures in other components a simple summation of FITs for these components may not be appropriate D 5 6 Consequence analysis The IEC 61508 series of standards Functional safety of electrical electronic programmable electronic safety related systems 5 is one examp
48. nagement For equipment with key control the keys should be placed under the control of a person appointed by management who should ensure their safe use storage and overall control Spare keys should be retained under strict control procedures by a nominated line manager Use test equipment of the lowest class necessary and practical for the task Do not use test equipment of a higher class than the location hazard level Area warning signs are required for locations exceeding hazard level 1M Area signs may be displayed in locations of lower classification System alarms especially those indicating that the APR or any other safety system is inoperable should be responded to so that repair takes place within specified time Live working practices for hazard levels 1 1M 2 2M and 3R When working on live energized systems e g when optical signals are being transmitted along the fibre of an OFCS it is recommended that the working practices listed in D 6 1 be used D 6 3 Working practices for hazard level 3B Working on an energized system sometimes referred to as live working in locations with hazard level 3B allocated is not recommended Responsible and adequate OFCS safety and training programmes should be established and maintained by management Personnel engaged in the installation and servicing of OFCS should observe all rules and report to management any potentially unsafe conditions or abnormal exposures to optica
49. nce with the specified radiation limit values are the same as those described for classification in IEC 60825 1 Measurements need to be taken under the appropriate conditions e g simulated fibre cable break and shall be based on the relevant clauses in IEC 60825 1 The assessment of the hazard level with and without automatic power reduction shall take place 1s after the reasonably foreseeable event for unrestricted locations unless measurement at a later time would result in a larger exposure 3s after the reasonably foreseeable event for restricted and controlled locations unless measurement at a later time would result in a larger exposure In circumstances where it is difficult to carry out direct measurements an assessment of hazard level based on calculations is acceptable For example the knowledge of the laser or amplifier power and fibre attenuation may allow an assessment of the hazard at any particular location For OFCS with automatic power reduction the hazard level will be determined by the accessible emission pulse or continuous wave after the time interval given above 1 s for unrestricted locations 3 s for restricted locations or controlled locations Additionally the MPE requirement in 4 8 2 shall be satisfied 4 8 2 Impact of using automatic power reduction features Where the OFCS uses an automatic power reduction feature to meet the limits of a hazard level that is lower than that which would have to
50. nd or connector end should be instructed not to view such points directly Under all circumstances only those viewing aids which provide the appropriate level of attenuation should be used 43 IS 14624 Part 2 2012 IEC 60825 2 2005 E 2 2 3 Only staff who have attended an optical fibre safety training course should be permitted to work on OFCS in a location with hazard level 3B E 2 2 4 Staff installing operating or maintaining OFCS and any associated test equipment in locations with hazard level 3B should ensure that untrained personnel are adequately protected E 2 2 5 It is possible that high loss points in the system could suffer from high temperatures when extremely high power levels hundreds of mW to several W are injected into the fibre NOTE An example of such a system is one that uses distributed Raman amplification technology The high temperature may lead to dangerous situations in equipment and offices Therefore in systems that normally transmit extremely high power the following action is recommended connectors should be cleaned very carefully so that the loss induced by connectors splices or bending at any point is reduced as far as possible E 2 3 Training programme The employer of staff installing or maintaining OFCS should establish and maintain an adequate programme for the control of fibre optic hazards Safety and training programmes should be instituted for staff working on fibre optic communication syste
51. nd s found not to be terminated for example single or matched spliced should be individually or collectively covered with material multiple appropriate for the wavelength and power when not being worked on They should not be readily visible and sharp ends should not be exposed Suitable methods for covering include the use of a splice protector or tape Always attach end caps to unmated connectors 37 IS 14624 Part 2 2012 IEC 60825 2 2005 Ribbon fibres Test cords Fibre off cuts Maintenance Cleaning Modification Board extenders Label damage Key control Test Equipment Signs Alarms D 6 2 Do not cleave ribbon fibres as an unseparated ribbon or use ribbon splicers unless authorized When using optical test cords the optical power source should be the last to be connected and the first to be disconnected Collect all fibre off cuts and dispose of them in an approved container The container itself should be disposed of in an approved manner Follow only approved instructions for operating and maintaining the system being worked on Use only approved methods for cleaning and preparing optical fibres and optical connectors Do not make any unauthorized modifications to any OFCS or associated equipment Board extenders should not be used on optical transmitter cards Do not power optical sources when they are outside transmitter racks Report damaged or missing optical safety labels to line ma
52. nications systems would be repaired within one day therefore MTTR 24 hours Systems that do not test the safety related systems may operate unattended for long periods but sometimes these systems are likely to be upgraded repaired tested or replaced every couple of years Therefore the mean time to repair can sometimes be considered to be 104 h or MTTR 104 h which is in the order of one year Table D 12 Determination of equipment monitoring classification Diagnostic testing and monitoring Classification Mean time to of safety related system repair M Frequent or continuous diagnostic testing and 1 day 24 h monitoring performed on the safety related system No monitoring but frequent diagnostic testing 1 year 104 h M3 No monitoring and no testing system is taken out 20 years 2x105 h of service before the specified end of life of the APR 36 IS 14624 Part 2 2012 IEC 60825 2 2005 With this information the FIT rate can now be determined As an example consider a communication system operating at 1550 nm where the optical power under normal operation no fault detected exceeds Class 1M but is below the upper limit of Class 3B Let us say that we wish to enable the OFCS to operate in an unrestricted location To facilitate this it is necessary for the radiation accessible under reasonably foreseeable fault conditions to be limited to hazard level 1 and given the Class of laser emitter an APR system is needed
53. niques to achieve a lower less hazardous hazard level based on the normal power in the fibre and the speed of automatic power reduction 45 IS 14624 Part 2 2012 IEC 60825 2 2005 F 3 Rationale to definitions 3 1 3 4 to 3 11 and to Clause 4 Large portions of OFCS can sometimes be classed as not accessible under reasonably foreseeable conditions F 4 Rationale to 4 8 1 and 4 8 2 The philosophy of these subclauses is based on assumptions that already exist in Parts 1 and 2 of IEC 60825 The clause requires that the MPE not be exceeded if any person is exposed to radiation emerging from the port or fracture from the instant of break or disconnection The power is assumed to remain constant at its maximum value until the shutdown time has expired a Unrestricted locations The 1s shutdown for unrestricted areas is consistent with 4 8 1 of IEC 60825 2 which states that the assessment of the hazard level shall take place 1 s after the reasonably foreseeable event The 100 mm distance is consistent with Table 10 of IEC 60825 1 Even if a fibre is intentionally cut it is highly unlikely that within 1s a person can get within 100 mm and position collimating optics be adversely exposed Also one must keep in mind that optical signals are attenuated as they move down the fibre so the output at the failure in the unrestricted area may be considerably lower than at the transmitter or amplifier b Restricted locations
54. nsmission system using multimode fibre of 50 um core diameter and a numerical aperture 0 2 0 02 carries six optical signals at wavelengths of 840 nm 870 nm 1 290 nm 1300 nm 1310 nm and 1320nm Each of these signals has a maximum time averaged power of 8 dBm 0 16 mW Determine the hazard level at the transmitter site In the absence of any other information concerning the transmitter emission duration when a connector is removed assume that no shut down system operates and then determine the hazard level based on the power levels accessible at the transmitter connector removing the connector is a reasonably foreseeable event Assess on the basis of f 100s emission duration for unintended viewing see 8 4 e of IEC 60825 1 Table 5 of IEC 60825 1 indicates that the effects of all wavelengths are additive The evaluation must therefore be made on the basis of the ratio of the accessible emission at each wavelength to the AEL for the applicable class at that wavelength see 8 4 b of IEC 60825 1 Note however that the AELs are constant in the wavelength range 1 200 nm to 1 400 nm hence the four signals in the vicinity of 1 300 nm may be considered as a single signal with a power level equal to the sum of powers in those signals First compare the emission levels with the AEL for Class 1 Since we have a small source with 50 um core diameter the angular subtense of the source is 0 5 mrad lt Qmin To 10 s See IEC 60825
55. nt with the disabled APR are included in the documentation NOTE 1 Except where otherwise explicitly stated this standard does not permit end to end OFCS to operate if accessible locations within that system are hazard level 4 If the transmitting power of a transmitter amplifier etc is Class 4 and the APR has been disabled then the result would be accessible locations operating at hazard level 4 Nevertheless it is recognised that it may be necessary to disable the APR in certain conditions but these conditions need to be well controlled and time limited so that the probability of exposure to a Class 4 radiation is very low NOTE 2 Regarding condition 5 an example of a suitable engineering means is a control system that automatically re enables the APR as soon as practicable after a time interval that is long enough to complete whatever task that caused the APR to be initially deactivated 4 6 Labelling or marking 4 6 1 General requirements Except as identified below each optical connector splice box or other part emitting radiation when opened shall be marked e g with a label sleeve tag tape etc if the hazard level at the location is in excess of hazard level 1 The marking shall be coloured yellow with the imprint of the warning label according to IEC 60825 1 and the explanatory label in IEC 60825 1 If XX is the hazard level assigned to the location then the explanatory text shall bear the words hazard level XX It i
56. nuator e Protective enclosures and housings f Fibre distribution frames 17 IS 14624 Part 2 2012 IEC 60825 2 2005 D 2 3 Typical operating functions a Installation b Operation c Maintenance d Servicing e Fault finding f Measurement including optical time domain reflectometry OTDR D 3 OFCS power limits The maximum mean power for each hazard level for the most important wavelengths and optical fibre types used in OFCS is presented in Table D 1 For most typical systems with duty cycles between 10 and 100 the peak power can be allowed to increase as the duty cycle decreases However for duty cycles lt 50 it is most straightforward to limit the peak powers to twice these mean power limits although IEC 60825 1 can be used for a more sophisticated analysis in order to identify any increase in peak powers permissible for these types of systems This is especially valid when visible sources with wavelengths in the photochemical hazard area are used NOTE For the most common single mode and multimode fibres the point source limits have to be applied Fibres with core diameters above 150 um e g plastic optical fibre POF and hard clad silica fibre HCS have to be considered as intermediate extended sources However the applicable apparent source size for the determination of the factor Cg may depend on the actual degree of mode filling Table D 1 OFCS power limits for 11 um single mode SM fibres an
57. onducted by the responsible organization NOTE Whereas IEC 60825 1 refers to single fault conditions it may be reasonably foreseeable that more than one fault will combine to cause a dangerous situation 26 IS 14624 Part 2 2012 IEC 60825 2 2005 b Service conditions often result in higher hazard levels see Clause 5 These should be considered by the responsible organization and persons Examples are introduction of high power or amplified optical time domain reflectometer pulses into an operating fibre network failure or overriding of the APR see 4 7 1e c Changing of components system parameters or the network structure may result in changed hazard levels Examples are replacement of conventional bundled fibre cables by ribbon cables this may be beyond the direct supervision of the network manager change of the modulation scheme change in transmitter circuit pack power or wavelength addition change of optical amplifiers etc D 5 Fault analysis Explanation and guidance Fault analysis is necessary for systems where the optical output is dependent on the integrity of other components and the performance of the circuit design It is recommended that the manufacturer or operator should carry out a fault analysis D 5 1 Definitions For the purpose of this Clause D 5 the following definition applies FITs an indicator of reliability defined as the number of failures per 10 h D 5 2 Fault analysis Hazard level
58. r unpredictable degree of mode mixing This mode mixing variability is also a potential problem when trying to evaluate these wavelengths on true multimode fibre If it is necessary to calculate a value for these cases the assumption that the fibre carries all of its power in the fundamental mode and use of the single mode equations will yield a conservative value NOTE 5 Multimode fibres with core diameters above 150 um These fibres have to be considered as intermediate extended sources e g hard clad silica HCS fibres with 200 um or plastic optical fibres with 1000 um core diameter The applicable source size may depend on the degree of mode filling and should be determined in detail before calculating the limit values NOTE 6 Hazard level 2 limits It can be shown that for apparent source sizes smaller than 33 mrad most cases in fibre communication techniques the hazard level 2 limits are always lower than the appropriate hazard level 1M limits Safe for the unaided eye but potentially unsafe when using optical instruments NOTE 7 Multiple fibres and ribbon cables The limits in the table are calculated for single fibres only If multiple fibres or ribbon fibres with single fibres located in close proximity to each other have to be assessed each individual fibre and each possible grouping of the fibres has to be evaluated NOTE 8 1 420 nm figure The 1 420 nm figure is calculated for the 1420 nm to 1 500 nm Raman range D 4 Haza
59. r precautions can be adopted ensure adequate warnings are provided to individuals regarding the potential hazards associated with OFCS through the use of signs labels and instructions Annex A gives a more detailed rationale for this part of IEC 60825 The safety of an OFCS depends to a significant degree on the characteristics of the equipment forming that system Depending on the characteristics of the equipment it may be necessary to mark safety relevant information on the product or include it within the instructions for use IS 14624 Part 2 2012 IEC 60825 2 2005 Where required by the level of potential hazard it places the responsibility for the safe deployment and use of these systems on the installer or end user operating organization or both This standard places the responsibility for adherence to safety instructions during installation and service operations on the installation organization and service organizations as appropriate and operation and maintenance functions on the end user or Operating organization It is recognised that the user of this standard may fall into one or more of the aforementioned categories of manufacturer installation organization end user or operating organization 2 Normative references The following referenced documents are indispensable for the application of this document For dated references only the edition cited applies For undated references the latest edition of the refer
60. ration or maintenance of fibre optic communication systems the responsibilities in relation to laser safety should be clearly defined by the operator In summary the primary differences between IEC 60825 1 and this Part 2 are as follows A whole OFCS will not be classified as required by IEC 60825 1 This is because under intended operation the optical radiation is totally enclosed and it can be argued that a rigorous interpretation of IEC 60825 1 would give a Class 1 allocation to all systems which may not reflect the potential hazard accurately However if the source can be operated separately it should be classified according to IEC 60825 1 Each accessible location in the extended enclosed optical transmission system will be designated by a hazard level on similar procedures as those for classification in IEC 60825 1 but this level will be based not on accessible radiation but on radiation that could become accessible under reasonably foreseeable circumstances e g a fibre cable break a disconnected fibre connector etc The nature of the safety precautions required for any particular hazard level will depend on the type of location i e domestic premises industrial areas where there would be limited access and switching centres where there could be controlled access For example it is specified that in the home a disconnected fibre connector should only be able to emit radiation corresponding to Class 1 or 2 whilst in
61. rd level evaluation examples D 4 1 Multiple wavelengths over the same fibre When more than one wavelength is transmitted along a single fibre such as on a wavelength division multiplex WDM system then the hazard level depends on both the power levels and on whether the wavelengths are additive For skin exposure to wavelengths usually used in OFCS the hazards are always additive For most fibre systems 1 400 nm is the point at which addition conditions change 19 IS 14624 Part 2 2012 IEC 60825 2 2005 a if two wavelengths are both below 1 400 nm they add i e the combined hazard is higher b if two wavelengths are both above 1 400 nm they add i e the combined hazard is higher c if one wavelength is above 1 400 nm and one is below then hazards do not add i e the combined hazard does not increase It is necessary to calculate separately for skin and retinal hazards To calculate the hazard level for a multi wavelength system it is necessary to calculate the system power at each wavelength as a proportion of the AEL for that Class at that wavelength for example 25 60 etc up to 100 and then add these components together If the totalled proportion exceeds 1 100 then the hazard level exceeds the accessible emission limits for that Class This procedure should also be used when determining the APR timing by using the MPE table instead of the AEL tables D 4 1 1 Multi wavelength example An optical tra
62. rds The following is a hypothetical and very conservative example of an approach for determining a SIL level It is based on the risk graph method in Annex D of IEC 61508 5 D 5 6 1 Example for consequence analysis Risk with no safety related systems in place is considered to be a function of the frequency of the hazardous event and the consequences of the event For this example a risk graph method is used to determine the SIL value The figure below is the risk graph taken from one of the IEC 61508 standards 31 IS 14624 Part 2 2012 IEC 60825 2 2005 C1 Starting point for risk reduction estimation C Consequence risk parameter F Frequency and exposure time risk parameter P Possibility of avoiding hazard risk parameter W Probability of the unwanted occurrence a b c h Estimates of the required risk reduction for the SRSs a b c d e f g h represent the necessary minimum risk reduction The link between the necessary minimum risk reduction and the safety integrity level is shown in the table Necessary minimum risk Safety integrity level reduction P No safety requirements P Neonat No special safety requirements See An ere SRS is not sufficient Figure D 3 Risk graph example from IEC 61508 5 Clause D 5 D 5 6 1 1 Step 1 Consequence evaluation In the 61508 standard four consequence levels are classified as shown in Table D 6 below In the ca
63. rios In addition the APR shall be designed to have an adequate level of reliability see Note 1 NOTE 1 Examples of calculating the reliability of APR systems are given in Clause D 5 NOTE 2 The restart interval described in the following scenarios is wavelength dependent as described in IEC 60825 1 4 5 1 Automatic restart In the case where the restart is initiated automatically the timing and power of the restart process shall be restricted such that the hazard level assigned to each accessible location of the system shall not be exceeded 4 5 2 Manual restart with assured continuity In the case where the restart is initiated manually and the continuity of the communications path is assured by the use of administrative controls or other means the timing and power of the restart process is not restricted see Note 3 The manufacturer s instructions shall specify that administrative controls or other means must take account of the fact that the assigned hazard level at any accessible location may be exceeded during this restart procedure NOTE 3 Since in this case the timing and power of the restart process is not restricted the administrative or other controls will need to take into consideration any increased risk of new hazards such as fire It is important that these additional controls be documented in the appropriate service instructions 4 5 3 Manual restart without assured continuity In the case where the restart is in
64. s FMEA Failure Mode Mechanism Distributions 1991 FMD 91 Reliability Analysis Center US Dept of Defense 1991 Prepared by Reliability Analysis Center PO Box 4700 Rome NY BT Handbook of Reliability Data for Components Used in Telecommunications Systems 1995 Issue 5 Copies available from ILI Index House Ascot Berkshire SL5 7EU UKAS Document NIS 20 Uncertainties of Measurement for Electrical Product Testing Draft 2 Jan 1992 IEC 61508 all parts Functional safety of electrical electronic programmable electronic safety related systems IEC 60794 1 1 Optical fibre cables Part 1 1 Generic specification General IEC 60794 1 2 Optical fibre cables Part 1 2 Generic specification Basic optical cable test procedures IEC 60794 2 Optical fibre cables Part 2 Indoor cables Sectional specification IEC 60794 3 Optical fibre cables Part 3 Sectional specification Outdoor cables IEC 60794 4 1 Optical fibre cables Part 4 1 Aerial optical cables for high voltage power lines IEC 60794 3 10 Optical fibre cables Part 3 10 Outdoor cables Family specification for duct and directly buried optical telecommunication cables IEC 60794 3 20 Optical fibre cables Part 3 20 Outdoor cables Family specification for optical self supporting aerial telecommunication cables IEC 60950 1 2001 Information technology equipment Safety Part 1 General requirements Nonelectronic parts rel
65. s ships or other vehicles c Locations with unrestricted access see 3 15 domestic premises services industries that are open to the general public e g shops and hotels public areas on trains ships or other vehicles open public areas such as parks streets etc non secured areas within business industrial commercial premises where members of the public are permitted to have access such as some office environments OFCS may pass through unrestricted public areas for example in the home restricted areas within industrial premises as well as controlled areas such as cable ducts or street cabinets Optical local area networks LANs may be deployed entirely within restricted business premises Fibre systems may be entirely in unrestricted domestic premises such as hi fi inter connections For requirements on infra red IR wireless LANs or free space optical systems see separate applicable part of IEC 60825 12 16 D 2 2 Typical system components a Fibre cables single fibre multiple fibre ribbon construction single mode multimode all dielectric or hybrid construction carrying single multiple wavelengths uni bidirectional fibre communications power feeding b Optical sources LEDs VCSEL Fabry Perot or DFB lasers pump lasers optical amplifiers bulk distributed continuous low high frequency emission c Connectors simplex duplex multiway hybrid d Power splitters wavelength multiplexers atte
66. s are assessed under reasonably foreseeable fault conditions The purpose of fault analysis is to identify failures in the optical control circuits that could have significant consequences affecting the assigned hazard level For example it is permitted for the lasers used in locations with hazard level 1M to emit optical power exceeding the upper limit of hazard level 1M under normal operating conditions if an adequate APR feature is provided However in case of a fibre break the accessible radiation is reduced so that it is within the limits of hazard level 1M If however a fault in a component in the laser drive circuit or in the APR were to result in radiation exceeding the limits for hazard level 1M then a higher hazard level would have to be assigned An APR feature can comprise both hardware and software components both components should be taken into account when determining the reliability of the APR feature D 5 3 Fault probability levels No system is 100 fail safe since there is always a non zero probability that failures will occur To quantify the risk of exposure to hazardous radiation OFCS should be subject to fault analysis using recognized techniques D 5 4 Commonly used fault analysis techniques Commonly used fault analysis techniques are simulation of those faults that could be expected under reasonably foreseeable conditions failure modes effects and criticality analysis FMECA see IEC 60812 1 conseq
67. s of IEC 60825 1 and IEC 60825 2 to their specific application It does not contain any requirements This standard applies to OFCS In such systems the optical power can be transmitted for long distances beyond the optical source and measures need to be taken to ensure that the potential hazards from a broken communications path are minimised In order to know the extent of the potential hazard existing in an OFCS it is necessary to assign a hazard level to those locations that can become accessible this is similar to but replaces the designation of a Class to the equipment within IEC 60825 1 It is possible to configure an optical fibre communications system to act as a closed loop control system such that when the communications path is broken the transmitted signal is automatically reduced in power within a short period of time to a safe value It is therefore possible to have two systems one with automatic power reduction APR and another without APR both having the same hazard level and therefore the same degree of safety the signal level under normal operating conditions in the system with APR can then be much higher than the signal level in the system without APR Because the APR feature is critical to safety the reliability of this feature should be adequate and recommendations are provided in this Annex Whereas the Part 1 standard applies to discrete laser products this Part 2 applies to complete end to end systems Because the su
68. s permitted to reduce the marking in size provided that the result is legible For network elements containing laser or optical amplifiers it is the responsibility of the manufacturer of the network element to provide such labelling all other labelling is the responsibility of the operating organization Labelling or marking is not required in unrestricted locations for hazard level 1M or 2M restricted locations for hazard level 1M or 2M if the requirements for cable connectors in unrestricted locations are met see 4 4 1 controlled locations for hazard level 1M or 2M NOTE 1 Unlike the labelling requirements of IEC 60825 1 marking in restricted locations is mandatory for locations with hazard level 1M except as identified above NOTE 2 In unrestricted locations hazard level 1M or 2M is exempt from this requirement because access to radiation from a connector is limited to hazard level 1 by suitable means see 4 4 1 and the mechanical design of the fibre cables must be consistent with the relevant standard within the IEC 60794 series see 4 3 NOTE 3 In controlled locations hazard level 1M or 2M is exempt from this requirement because accessibility is limited to personnel with appropriate laser safety training see definition 3 13 IS 14624 Part 2 2012 IEC 60825 2 2005 4 6 2 Marking of connectors of optical transmitters and optical amplifiers For connectors of optical transmitters and optical amplifiers
69. s with accessible locations other than hazard level 1 or 2 the installation organization and or the service organization shall a provide adequate laser safety training of personnel responsible for carrying out installation and service activities b ensure that suitable access controls and warning labels are employed on controlled and restricted locations 4 7 3 Operating organization The operating organization has the ultimate responsibility for the safety of the end to end system This includes especially a identification of the location type at all accessible locations of the entire OFCS b ensuring that the hazard levels are not exceeded for those location types under reasonably foreseeable events IS 14624 Part 2 2012 IEC 60825 2 2005 c ensuring that installation and service is performed only by organizations with the capability of satisfying the requirements of 4 2 to 4 9 d ensuring that access to restricted and controlled locations is appropriately addressed with respect to laser safety e ensuring continuous compliance with system manufacturing operating installation service and safety requirements 4 8 Assessment of hazard level 4 8 1 Determination of hazard level The hazard level is determined by the measurement of the optical radiation that could become accessible following any reasonably foreseeable event e g fibre break during operation and maintenance The methods for the determination of complia
70. se of OFCS for skin or eye damage the consequence risk level could very conservatively be assigned C3 Table D 6 Consequence classification from IEC 61508 5 Table D 1 Consequence Risk Level Classification Serious permanent injury to one or more persons death to one person D 5 6 1 2 Step 2 Frequency evaluation In the IEC 61508 series of standards frequency and exposure time in the hazardous zone must be assessed and can be assigned one of two values as specified in Table D 7 below A very conservative estimate for an OFCS example is an assignment of risk level F3 32 IS 14624 Part 2 2012 IEC 60825 2 2005 Table D 7 Frequency classification from IEC 61508 5 Table D 1 Frequency of and exposure time Classification in the hazardous zone Risk Level Rare to more often exposure in the hazardous zone Frequent to permanent exposure in the hazardous zone D 5 6 1 3 Step 3 Evaluation of the possibility of avoiding the hazard In the standard the possibility of avoiding the hazardous event can be assigned one of two values as specified in Table D 8 below In this example an assignment of risk level P is made Table D 8 Possibility of avoiding hazard classification from IEC 61508 5 Table D 1 Possibility of avoiding the Classification hazardous event Risk level P Possible under certain conditions D 5 6 1 4 Step 4 Evaluation of the probability of the hazardous event taking place
71. sidered as service or maintenance operations Wherever possible diagnostic tests should be carried out in such a way as not to increase the hazard level at any location It may be necessary to have administrative controls which in some cases may involve a permit to work system When connecting test equipment due regard should be given to establishing the actual power levels introduced into the system in assessing the hazard E 1 2 The operating organization should develop and maintain clearly defined conditions under which the automatic power reduction feature can be overridden When the automatic power reduction feature has been overridden the hazard level should be reassessed by the operating organization The appropriate safety precautions described in 5 2 and its associated subclauses should be taken as appropriate to the reassessed hazard level E 1 3 Any viewing optics for fibre examination and splicing should be selected so that they reduce exposure to below the relevant maximum permissible exposure MPE and should be approved for use by the operating organization NOTE The marking of approved viewing optics with a label by the operating organization may be an acceptable solution E 1 4 Wherever reasonably practical servicing maintenance and repair should be carried out with no power propagating in the fibre Where this is not reasonably practicable the system should be operated at the lowest power consistent with the functional nee
72. ssigned to any accessible location within an OFCS at which under a reasonably foreseeable event human access to laser radiation in excess of the accessible emission limits of Class 3B for the applicable wavelengths and emission duration will not occur 3 11 hazard level 4 hazard level 4 is assigned to any accessible location within an OFCS at which under a reasonably foreseeable event human access to laser radiation in excess of the accessible emission limits of Class 3B for the applicable wavelengths and emission duration may occur NOTE This standard is applicable for the operation and maintenance of OFCS In order to achieve an adequate level of safety for persons who may come into contact with the optical transmission path hazard level 4 is not permitted within this standard It is permitted to use protection systems such as automatic power reduction to achieve the required hazard level where the transmitted power under normal operating conditions e g no fault exists in the fibre path exceeds that permitted for a particular location type For instance it is possible for accessible parts of an OFCS to be hazard level 1 even though the power transmitted down the fibre under normal operating conditions is Class 4 3 12 installation organization an organization or individual that is responsible for the installation of an OFCS 3 13 location with controlled access controlled location an accessible location where an engineering or admin
73. t such as a fibre break has caused the radiation to become accessible This maximum power value could be lower than the normal operating power in the fibre as a result of activation of the APR system Requirements are described in 4 8 1 4 2 Protective housing of OFCS Each OFCS shall have a protective housing which when in place prevents human access to laser radiation in excess of hazard level 1 limits under normal operating conditions 4 3 Fibre cables If the potential hazard at any accessible location within an OFCS is hazard level 1M 2M 3R or 3B then the fibre optic cable shall have mechanical properties appropriate to its physical location Cables for various physical locations are described in the IEC 60794 series Where necessary additional protection for example ducting conduit or raceway may be required for locations where the fibre would otherwise be susceptible to damage 4 4 Cable connectors The following requirements for cable connectors may be achieved by the mechanical design of the connectors or by the positioning of the connector or by any other suitable means Whichever means is chosen human access to radiation above that permitted for connectors in a particular location type shall be prevented NOTE The use of a tool for disconnection is one example of a mechanical solution 4 4 1 Unrestricted locations In unrestricted locations if the radiation level exceeds the accessible emission limits of Class 2
74. t to look A possibility might be to use a cleaving tool that stayed attached to the cleaved fibre end until it was inserted into a ribbon splicer that likewise prevented access during the whole operation 25 IS 14624 Part 2 2012 IEC 60825 2 2005 Once ribbon fibre is used in the network it will be difficult to control what type of system is put onto it D 4 6 Power diminution due to power splitters and fibre losses This power diminution may be taken into account for example at the customer side of a distribution network the hazard level after some length of fibre may be lower than at the distribution point Figure D 1 shows the layout of a typical passive optical network PON Exchange office External Customer Switch Ad ONU Services CY OL lt N a a ONU Services Z Splitters a Fibre Copper OLT Optical line termination ONU Optical network unit Figure D 1 PON passive optical network based system D 4 7 General considerations and examples a The assessment of hazard levels should always consider reasonably foreseeable fault conditions see 4 8 3 resulting from random failures in hardware components and systematic failures e g failure of software controlling the APR function Consequently it may be necessary to include multiple fault conditions a determination of the probability of such conditions occurring is to be c
75. tional Standard referred in this adopted standard and has decided that it is acceptable for use in conjunction with this standard International Standard Title IEC 60825 1 Safety of laser products Part 1 Equipment classification requirements and user s guide Only the English language text has been retained while adopting it in this Indian Standard and as such the page numbers given here are not the same as in the IEC Standard For the purpose of deciding whether a particular requirement of this standard is complied with the final value observed or calculated expressing the result of a test or analysis shall be rounded off in accordance with IS 2 1960 Rules for rounding off numerical values revised The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard IS 14624 Part 2 2012 IEC 60825 2 2005 Indian Standard SAFETY OF LASER PRODUCTS PART 2 SAFETY OF OPTICAL FIBRE COMMUNICATION SYSTEMS OFCS First Revision 1 Scope and object This Part 2 of IEC 60825 provides requirements and specific guidance for the safe operation and maintenance of optical fibre communication systems OFCS In these systems optical power may be accessible outside the confinements of transmitting equipment or at great distance from the optical source This Part 2 requires the assessment of hazard levels at accessible locations as a replacement for classifi
76. to energized fibre is reasonably foreseeable is when an energized system has one or several of its fibres disconnected at an optical connector A number of solutions exist to achieve a safer hazard level when disconnecting optical connectors For example one mechanical solution that can be considered is the use of shuttered connectors Such a solution provided the connectors meet the reliability characteristics outlined in Clause D 5 provides control of the exposure from unmated connectors These shutters should operate within 1s in unrestricted locations and 3s in restricted and controlled locations It should be noted that shutters might not be practical or desirable for controlling optical power levels exceeding hazard levels 1M 2M or 3R In these situations APR may be the only solution D 4 3 5 Submerged buried cable for undersea systems Certain undersea systems have the potential to carry substantial optical power levels Typically damage to fibre cable is incurred on the submerged portion not on the buried land portion Because the fibre cable is submerged an appropriate shipping vessel is necessary to retrieve the cable and repair it which may take hours or days to accomplish As automatic power reduction may not be appropriate or practical for these systems rigorous administrative controls including manual laser shutdown procedures may need to be employed This will ensure that proper working conditions are maintained below hazard
77. uence analysis see the IEC 61508 series of standards 5 27 IS 14624 Part 2 2012 IEC 60825 2 2005 D 5 5 Failure modes effects and criticality analysis If the chosen method of fault analysis is failure modes effects and criticality analysis then the probability of exceeding the accessible emission limits under reasonably foreseeable circumstances for the target hazard level should not exceed 500 FITs It is recommended that the manufacturer or operator should carry out a fault analysis NOTE On the basis of 500 FITs and the estimated amount of time an engineer works on live fibres throughout his working life the incident rate for the risk of injury to the eye is less than five HITs HITs is the number of hazard incidents per 109h For example in the UK the Health and Safety Executive considers an occupational risk of less than 5 43 HITs for accidents to be trivial D 5 5 1 Example of FMECA analysis for a simple laser drive circuit The purpose of the analysis is to provide a quantitative measure of the probability of the optical power exceeding Class 1M AEL The following example illustrates one recommended method Consider the simple circuit in Figure D 2 5V C1 Figure D 2 Simple laser drive circuit D 5 5 1 1 Step 1 identify critical components From circuit diagrams and parts lists identify all the components likely to affect the laser module Typically these include mean power control circuitry dat
78. uipment with higher optical output powers providing the accessible fibre ends and connectors at all locations are secured and labelled with the appropriate hazard level before testing proceeds E 2 1 4 Entry points to controlled areas with a hazard level of 3B should have a sign bearing the warning label according to Figure 14 in IEC 60825 1 and the explanatory label of Figure 15 of IEC 60825 1 bearing the words Hazard level 3B a sign limiting access to authorized persons only and explaining the existence of a potential hazard E 2 1 5 Each person engaged in the operation installation or service of an OFCS should observe all rules procedures and practices established for the safe operation of OFCS immediately notify the supervisor of conditions or practices that have the potential to cause personnel injury or property damage immediately report to the supervisor any known or suspected abnormal exposure to optical radiation E 2 2 Precautions in locations with hazard levels 1M 2M 3R and 3B E 2 2 1 Where possible optical transmission or test equipment should be shut down put into a low power state or disconnected before any work is done on exposed fibres connectors etc In that case unintentional switching on should be prevented by a remote control switch or another suitable method The status of the line power on or off should be clearly indicated E 2 2 2 Persons having access to any energized fibre e
79. ures demand MTTR is mean time to repair in hours and 109 is the conversion from failure rate in failures hour and FITs in failures 109 hours The following figure D 4 shows the relationship between FIT rate and mean time to repair a failed safety system The range for SIL level 1 safety systems has been highlighted FIT rate required to meet safety integrity levels 100 000 000 T 1 000 000 T L 2 Z 10 000 o g m 100 1 day 1 month 1 year 14 1 r ea H 1 10 100 1 000 10 000 Mean time to repair h Figure D 4 Graph of FIT rate and mean time to repair D 5 6 1 7 Step 7 Reducing the risk from systematic failures For SIL 1 IEC 61508 2 and IEC 61508 3 highly recommend at least the following methods to reduce systematic failures a program sequence monitoring e g watchdog logical monitoring of program sequence temporal monitoring with online check b software design using structured methods e g JSD MASCOT SADT Yourdon 35 IS 14624 Part 2 2012 IEC 60825 2 2005 c measures against voltage breakdown voltage variations overvoltage low voltage d separation of electrical energy lines from information lines e increase of interference immunity f measures against the physical environment e g temperature humidity water vibration dust corrosive substances g measures against temperature increase e g temperature sensor fan control thermal fuse temperature alarm
80. very low NOTE Examples of reasonably foreseeable events might include the following fibre cable break optical connector disconnection operator error or inattention to safe working practices Reckless use or use for completely inappropriate purposes is not considered as a reasonably foreseeable event 3 20 service organization an organization or individual that is responsible for the servicing of an OFCS 3 21 subassembly any discrete unit subsystem network element or module of an OFCS which contains an optical emitter or optical amplifier 4 Requirements 4 1 General This section defines the restrictions that are to be placed on an OFCS and on the location types in which an OFCS can operate in accordance with the hazard that arises from optical radiation becoming accessible as a result of a reasonably foreseeable event Whenever one or more alterations are made to an OFCS the organization responsible for that alteration shall make a determination of whether each alteration could affect the hazard level If the hazard level has changed the organization responsible for the alteration s shall re label those locations in the system that are accessible so as to ensure continued compliance with this standard Each accessible location within an OFCS shall be separately assessed to determine the hazard level at that location Where multiple communications systems are present at a location the hazard level for the location shall be the
81. without any safety related systems The last assignment is the probability of the hazardous event taking place without any safety related systems i e probability of unwanted occurrence see Table D 9 below For this example the risk level range of W W3 is assigned Table D 9 Classification of the probability of the unwanted occurrence from IEC 61508 5 Table D 1 Probability of the unwanted Classification occurrence risk level A very slight probability that the unwanted occurrences will come to pass and only a few unwanted occurrences are likely A slight probability that the unwanted occurrences will come to pass and a few unwanted occurrences are likely W3 A relatively high probability that the unwanted occurrences will come to pass and frequent unwanted occurrences are likely D 5 6 1 5 Step 5 Mapping onto the graph Mapping these parameters onto the risk graph Figure D 3 above yields under the most conservative conditions an assignment of a reliability level of SIL 1 for a skin or eye hazard The other methods described in the IEC 61508 series of standard also converge to SIL 1 using the same criteria 33 IS 14624 Part 2 2012 IEC 60825 2 2005 D 5 6 1 6 Step 6 Determination of the reliability of the APR system In the following steps only SIL 1 has been considered For SIL levels other than 1 refer to the IEC 61508 series of standards For these SIL levels hardware random failures hardware fault to
82. y normal transmitting power levels exceeding the acceptable hazard level for the particular location type protection systems such as automatic power reduction may be used to determine the actual hazard level 4 See 4 9 14 IS 14624 Part 2 2012 IEC 60825 2 2005 Annex C informative Methods of hazard safety analysis Some methods of hazard safety analysis include the following a preliminary hazard analysis PHA including circuit analysis This method may be used in its own right but is an essential first stage in the application of other methods of hazard safety assessment b consequence analysis see the IEC 61508 series of standards 5 c failure modes and effects analysis FMEA d failure modes effects and criticality analysis FMECA see IEC 60812 1 e fault tree analysis FTA f event tree analysis g hazards and operability studies HAZOPS Appropriate testing should be implemented to supplement the analysis whenever necessary The method of analysis and any assumptions made in the performance of the analysis should be stated by the manufacturer operator 15 IS 14624 Part 2 2012 IEC 60825 2 2005 Annex D informative Application notes for the safe use of OFCS D 1 Introduction This annex provides guidance on the application of this standard to specific practical situations It is an informative annex to assist the users of this standard in applying the requirement

IS 14624-2 (2012): Safety of laser products, Part 2: Safety of Optical

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