Last week I focused on Confined Spaces. This week I’d like to address Gas Detection, which
is especially important in Confined Spaces.
Workers can’t rely solely on their own sense of smell to keep them safe from a possible gas hazard. It takes proper maintenance and calibration of Gas Detection instruments to ensure their accuracy in identifying worker exposure to harmful gases in the workplace.
Occupational Health and Safety Administration (OSHA) reports that direct-reading portable gas monitors (DRPGMs) are designed to alert workers to toxic gases, as well as oxygen-deficient and combustible atmospheres that may exist in workplace environments, such as permit-required confined spaces, manholes, and other enclosed spaces. Several OSHA standards require the use of gas monitors. OSHA recommends developing standard procedures for calibrating and using DRPGMs that include documentation to verify the proper maintenance and calibration of the instruments.
There is a real danger to instrument inaccuracy due to improper or irregular maintenance and calibration. Inaccuracy can lead to exposure to hazardous levels of toxic gases or to an oxygen-deficient atmosphere, which can lead to serious injuries or illness, and even death. Flammable gas explosions can be catastrophic, resulting in injuries and death, in addition to the destruction of property.
OSHA recommends that the best way to verify that a DRPGM detects gas accurately 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.
Furthermore, OSHA has shared that gas detectors should be calibrated before each use. A full calibration for a 4-gas monitor takes about 5 minutes.
OSHA refers on their website to recommendations from the International Safety Equipment Association (ISEA), a trade association for manufacturers of protective equipment, including environmental monitoring instruments. The ISEA recommends, at a minimum, verification of sensor accuracy before each day’s use. This does not necessarily include calibration, but would require bump testing – the process of subjecting the gas monitor to the gas(es) they are supposed to detect and making sure they register – each day.
Accurate Readings through Calibration
Operators use DRPGMs to detect the presence and concentration of toxic and combustible gases, as well as oxygen deficiency or oxygen enrichment (which OSHA identifies as a fire and explosion hazard). Workers need to use these instruments when working in areas with potential hazardous atmospheres.
"Calibration" refers to an instrument's measuring accuracy relative to a known traceable concentration of test gas. DRPGMs compare the sensor's response to a known concentration of the test gas. When testing, 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 gives you the reference point.
Sensor responsiveness will vary with workplace conditions, factors such as temperature and humidity. Therefore, it’s recommended that operators 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 need to conform to the manufacturer's instructions, internal company policy, and the appropriate regulatory agency guidelines. Employers should keep calibration records for the life of each instrument. OSHA believes these records help operators 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
A reading becomes unreliable when an instrument's reference point shifts. The general rule of thumb is that “calibration drift" happens to all sensors over time. An instrument that experiences calibration drift can still measure the quantity of gas present, but it won’t 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.
OSHA reports that 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 confirm a DRPGM's accuracy. 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. While a DRPGM may appear undamaged during visual inspection, it actually could be damaged internally. When this happens, the operator should replace the damaged sensor or have qualified personnel service the sensor. OSHA recommends following the manufacturer's instructions regarding sensor replacement and servicing.
Keep Workers Safe
It’s critical to keep proper, regular instrument calibration in order 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. This detection is vital in warning users of hazardous conditions before the conditions reach dangerous levels.
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. Verify the function and accuracy of instruments every day to help ensure that each worker goes home safely.
Visit arbill.com for more information on how to learn more about keeping your workers safe through effective training, and our full line of safety products.
Have a safe day!