OSHA recommends developing standard procedures for calibrating and using gas monitors that include documentation to verify the proper maintenance and calibration of the instruments.
Instrument 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 monitor 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 ISEA recommends, at a minimum, verifying the operational capability of these instruments before each day's use, with additional testing conducted as necessary.
The following are a few basic calibration rules for gas monitors:
- 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 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 test everyone responsible for performing DRPGM calibration.
When to Test?
Calibration - Before first use and monthly thereafter.
Bump Test - Prior to each day’s use.
Between regular calibrations, a calibration should be performed immediately following each of these incidents: the unit falls, is dropped, or experiences another significant impact; is exposed to water; fails a bump test; or has been repeatedly exposed to an over-range (positive or negative) gas concentration. A calibration is also recommended after the installation of a new (or replacement) sensor. These recommendations are based on field data, safe work procedures, industry best practices, and regulatory standards to ensure worker safety.
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