OSHA Calibration Frequency Bulletin
Contents
1. area is above the warning level and approaching a hazardous level Whether a DRPGM provides a warning or danger alarm at the proper concentration depends on its detection capabilities its ability to translate its findings into an accurate reading and the presence of interfering gases see Calibration Drift and Causes above Bump Tests Calibration Checks and Full Calibration Bump Test or Function Check This is a qualitative function check in which a challenge gas is passed over the sensor s at a concentration and exposure time sufficient to activate all alarm settings The purpose of this check is to confirm that gas can get to the sensor s and that all the instrument s alarms are functional The bump test or function check does not provide a measure of the instrument s accuracy When performing a bump test the challenge gas concentration should trigger the DRPGM s alarm s Calibration Check or Full Calibration There are two methods for verifying DRPGM accuracy a calibration check and a full calibration Each method is appropriate under certain conditions A calibration check verifies that the sensor s and alarms respond within the manufacturer s acceptable limits by exposing the instrument to a test gas The operator compares the reading to the test gas concentration as indicated on the cylinder containing the test gas If the instrument s response is within the acceptable range of the test gas concentration typically 10 20 of th2. Operation for Direct Reading Portable Gas Monitors http www safetyequipment org userfiles file calibration_statement 2010 mar4 pdf PDF Footnotes 1 See link to the ISEA Statement on Validation of Operation for Direct Reading Portable Gas Monitors at the end of this SHIB 2 See the discussion of calibration checks and full calibration later in this SHIB 3 The Supplementary Materials for NIST Policy Review page on NIST s website at http www nist gov traceability suppl_matls_for_nist_policy_rev cfm accessed 08 15 2013 provides the following definition of traceable to NIST According to the internationally recognized VIM definition metrological traceability is a property of a measurement result by which that result is related to specified reference standards not to institutions Accordingly the phrase traceable to NIST in its most proper sense is shorthand for metrologically traceable to NIST s practical realization of the definition of a measurement unit see 2 43 in JCGM 200 2008 International vocabulary of metrology Basic and general concepts and associated terms VIM Third Edition 2008 Accessibility Assistance Contact OSHA s Directorate of Science Technology and Emergency Management at 202 639 2300 for assistance accessing PDF materials All other documents that are not PDF materials or formatted for the web are available as Microsoft Office formats and videos and are noted accordingly If additional ass
3. curacy relative to a known traceable concentration of test gas DRPGMs compare the sensor s response to a known concentration of the test gas To confirm the validity of this comparison it is important to ensure the calibration gas has not expired always check the expiration date of the gas before usage The instrument s response to the calibration gas serves as the reference point The responsiveness of sensors will vary with workplace environmental conditions such as temperature and humidity Therefore to the degree possible operators should calibrate sensors in environmental conditions that are the same as or similar to the actual workplace conditions Follow the manufacturer s guidelines for proper calibration Standard procedures for regular calibration that conform to the manufacturer s instructions internal company policy and or the appropriate regulatory agency guidelines will help to ensure that calibration procedures are readily followed by the DRPGM operators and that the instruments are operable and accurate when used Employers should keep calibration records for the life of each instrument This record enables operators to quickly identify a DRPGM that has a history of excessive maintenance repair or is prone to erratic readings and to track drift of the sensors to determine when they need replacement Calibration Drift and Causes When an instrument s reference point shifts the reading will shift accordingly and be unreliable Th
4. e test gas concentration then the calibration check verified the instrument s accuracy Note OSHA recommends that operators check with the instrument s manufacturer for the acceptable tolerance ranges An operator should zero an instrument reset the reference point in some cases zero air gas may be needed before conducting the calibration check to ensure that the calibration check results are accurate When performing a calibration check the test gas concentration should be high enough to trigger the instrument s alarm s If the calibration check results are not within the acceptable range the operator should perform a full calibration A full calibration adjusts the instrument s reading to coincide with a known concentration i e certified standard of test gas Test gas used for calibration gas should always be certified using a standard traceable to the National Institute of Standards and Technology NIST When to Perform a Bump Test and When to Perform a Full Calibration In the past there has been some confusion regarding proper calibration procedures and frequency To clarify this issue ISEA updated its position statement on instrument calibration in 2010 stating A bump test or calibration check of portable gas monitors should be conducted before each day s use in accordance with the manufacturer s instructions If an instrument fails a bump test or a calibration check the operator should perform a full calibration on it be
5. fore using it If the instrument fails the full calibration the employer should remove it from service Contact the manufacturer for assistance or service Calibration Rules The following are a few basic calibration rules for DRPGMs Follow the manufacturer s guidelines for proper calibration Operators cannot perform any job including DRPGM calibration properly or safely without the right tools The type and concentration of calibration test gas sample tubing flow regulators and calibration adapters are key links in the calibration chain Operators should conduct any testing to verify the operation of the gas monitor in an environment that is the same as or similar to the working conditions e g temperature humidity atmospheric pressure Only use a certified traceable test gas and do so before its expiration date The instrument can only be as accurate as the test gas used to calibrate it Be certain that the supplier can provide a certificate of analysis for every test gas cylinder The concentration of the test gas particularly reactive gases such as hydrogen sulfide and chlorine will only remain stable for a limited period Never use a test gas after its expiration date Train DRPGM operators on the proper methods of calibration Most instruments are designed to be field calibrated with detailed instructions provided in the manufacturer s user manual training videos or computer based training modules Employers should train and te
6. inaccuracy due to improper or irregular maintenance and calibration can lead to exposure to hazardous levels of toxic gases or to an oxygen deficient atmosphere This exposure can cause workers to suffer serious injuries or illness and even death Flammable gas explosions are often catastrophic resulting in worker injuries and death or destruction of property The best way to verify that a DRPGM detects gas accurately and reliably is to test it with a known concentration of gas This procedure will verify whether the sensors in the instrument respond accurately and whether the alarms function properly The International Safety Equipment Association ISEA founded in 1933 is a trade association for manufacturers of protective equipment including DRPGMs The ISEA recommends at a minimum verifying the operational capability of these instruments before each day s use with additional testing conducted as necessary This SHIB incorporates recommendations developed by the ISEA Calibration The Key to Accurate Readings Operators use DRPGMs to detect the presence and concentration of toxic and combustible gases as well as oxygen deficiency or oxygen enrichment which is a fire and explosion hazard Workers must not rely solely on their sense of smell to alert them to these hazards Employers should ensure that workers use these instruments when working in areas with potential hazardous atmospheres Calibration refers to an instrument s measuring ac
7. ions in this Safety and Health Information Bulletin is not in itself a violation of the General Duty Clause Citations can only be based on standards regulations and the General Duty Clause The information in this Safety and Health Information Bulletin SHIB provides workers and employers guidance on calibrating and testing direct reading portable gas monitors hereafter DRPGMs or instruments These instruments protect workers from unseen workplace gas hazards Proper maintenance and calibration of the instruments ensures their accuracy in detecting worker exposure to harmful gases in the workplace Follow the manufacturer s recommendations with regard to calibrating the instruments Introduction DRPGMs are designed to alert workers to toxic gases as well as oxygen deficient and combustible atmospheres that may exist in their workplace environments such as permit required confined spaces manholes and other enclosed spaces Several OSHA standards require the use of gas monitors See paragraph c 5 ii C of 29 CFR 1910 146 Permit required confined spaces paragraph c 6 of 29 CFR 1910 120 Hazardous waste operations and emergency response and section 5 Entry into bins silos and tanks of Appendix A of 29 CFR 1910 272 Grain handling facilities OSHA recommends developing standard procedures for calibrating and using DRPGMs that include documentation to verify the proper maintenance and calibration of the instruments Instrument
8. is is called calibration drift and it happens to all sensors over time An instrument that experiences calibration drift can still measure the quantity of gas present but it cannot convert this information into an accurate numerical reading Calibration checks or full calibration with a traceable gas concentration will verify or update the instrument s reference point Operators should conduct these procedures daily or more frequently if needed to ensure that the instrument will continue to produce accurate readings Calibration drift occurs most often because of Degradation caused by exposure to phosphates Degradation of phosphorus containing components Degradation of lead containing components Gradual chemical degradation of sensors and drift in electronic components that occur normally over time Use in extreme environmental conditions such as high low temperature and humidity and high levels of airborne particulates Exposure to high concentrations of the target gases and vapors Exposure of catalytic hot bead LEL sensors in the instruments to volatile silicones hydride gases halogenated hydrocarbons and sulfide gases Exposure of electrochemical toxic gas sensors to solvent vapors and highly corrosive gases Handling jostling of the equipment causing enough vibration or shock over time to affect electronic components and circuitry Operators should validate a DRPGM s operability when any of these conditions occurs
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10. o 5s mt Tus pla eS Vi eth oe a ey p A oe C D i a Tay I j plat Ls thts mete Ea ae fy Menu Occupational Safety amp Health Administration We Can Help Safety and Health Information Bulletins Calibrating and Testing Direct Reading Portable Gas Monitors U S Department of Labor Occupational Safety and Health Administration Directorate of Technical Support and Emergency Management Office of Science and Technology Assessment Calibrating and Testing Direct Reading Portable Gas Monitors l l SHIB 09 30 2013 Safety and Health Information Bulletin This Safety and Health Information Bulletin is not a standard or regulation and it creates no new legal obligations The Bulletin is advisory in nature informational in content and is intended to assist employers in providing a safe and healthful workplace Pursuant to the Occupational Safety and Health Act employers must comply with hazard specific safety and health standards and regulations promulgated by OSHA or by a state with an OSHA approved state plan In addition pursuant to Section 5 a 1 the General Duty Clause of the Act employers must provide their employees with a workplace free from recognized hazards likely to cause death or serious physical harm Employers can be cited for violating the General Duty Clause if there is a recognized hazard and they do not take reasonable steps to prevent or abate the hazard However failure to implement any recommendat
11. or is suspected during use When attempting to calibrate an instrument after exposure to these conditions the sensor often will either display a failure message or will not allow the operator to fully adjust the display reading Harsh operating and storage conditions can affect instrument performance leading to inaccurate readings or even failure While a DRPGM may appear undamaged during visual inspection it actually could be damaged internally At this point the operator should replace the damaged sensor or have qualified personnel service the sensor Be sure to follow the manufacturer s instructions regarding sensor replacement and servicing Worker Safety The Number One Reason for Proper and Regular Calibration The primary reason for proper regular instrument calibration is to provide accurate gas concentration readings that could prevent worker illness injury or death Correctly calibrating an instrument helps to ensure that the DRPGM will respond accurately to the gases it is designed to detect thereby warning users of hazardous conditions before the conditions reach dangerous levels Some DRPGMs have two levels of alarms warning and danger The warning alarm alerts the operator and workers that the work environment has a detectable elevated concentration of toxic gas and is therefore potentially hazardous The danger alarm indicates that the toxic gas concentration exceeds the programmed hazard threshold and that the toxic gas in the work
12. st everyone responsible for performing DRPGM calibration Conclusion Many workplaces have a risk of injury illness or death from respiratory hazards such as oxygen deficiency and the combustible or toxic gases DRPGM technology and products exist to minimize such risks Properly verifying the function and accuracy of instruments before each day s use will help to ensure that each worker finishes the job safely For more information contact OSHA at 1 800 321 6742 OSHA OSHA Main Number www osha gov Twenty seven states and territories operate their own occupational safety and health programs approved by OSHA States enforce similar standards that may have different or additional requirements A list of state plans is available at http www osha gov dcsp smallbusiness index html OSHA s On site Consultation Program offers free and confidential advice to small and medium sized businesses in all states across the country with priority given to high hazard worksites On site Consultation Programs are separate from enforcement and do not result in penalties or citations To locate the OSHA On site Consultation Program nearest you call 1 800 321 6742 OSHA or visit http www osha gov dcsp smallbusiness index html On Line Resources International Safety Equipment Association ISEA 1901 North Moore Street Arlington VA 22209 1762 703 525 1695 http www safetyequipment org OSHA Alliance 2003 2005 ISEA Statement on Validation of
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