Rule 1: Perform a *Bump test prior to each use; calibrate if the confined space gas meter is out of calibration by more than +/- 10% of the test gas value.
For example: if you apply 50% LEL methane to a combustible sensor, +/-10% of 50% LEL is +/- 5% LEL (acceptable tolerance 45%-55% LEL). If you apply 25 ppm H2S to an H2S sensor, then +/-10% of 25 PPM is +/- 2.5 PPM (acceptable tolerance 22.5 PPM – 27.5 PPM).
Rule 2: Use a certified traceable test gas, recommended by the manufacturer for the calibration of the confined space gas meter, which has not expired.
Rule 3: Use the test gas in a well-ventilated area or under a vent hood to minimize exposure.
Rule 4: If the gas meter is equipped with a sample pump; the pump, hose(s), probe, and filters used with the gas meter, should be attached during a bump test. Once the pump, hose(s), probe, and filters are attached; test for air leakage by blocking the inlet. If there is no leakage, the pump should stall and a low flow alarm should sound, if so equipped. Correct any air leaks prior to performing a bump test or using the gas meter.
Rule 5: Test response time and repeatability. It is important to make sure the sensor(s) respond quickly and within manufacturer specifications. Repeatable results are also very important, so test the meter with gas more than once. These specifications are usually outlined in the sales literature or owner’s manual.
Rule 6: Perform a visual inspection of the meter and all accessories prior to use. Some of the items to check are; dirty filters, cut hoses, cracked probe filters, button-switch operation, leaky batteries, damaged display, damaged case/housing, corrosion, damaged wires, and missing or loose hardware.
Rule 7: Remove any meter from use that requires calibration or repair. OSHA 1910.146(d)(4) states that an employer must provide equipment that is properly maintained.
Rule 8: Maintain test and calibration records. OSHA Safety and Health Information Bulletin SHIB 09-30-2013 states “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 the drift of the sensors to determine when they need replacement.”
*Bump Test: This is a qualitative function check in which test 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.
This article was based on the following sources
Safety and Health Information Bulletin SHIB 09-30-2013 https://www.osha.gov/dts/shib/shib093013.html
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