What is the proper method for calibrating a personal air sampling pump used for measuring worker exposure to airborne contaminants?

The proper method for calibrating a personal air sampling pump involves using a calibrated primary standard, such as a dry gas meter or a bubble flow meter, to verify the pump's flow rate. Calibration is essential for ensuring accurate measurement of worker exposure to airborne contaminants. The process begins by assembling the sampling train, which includes the air sampling pump, tubing, a sampling media (e.g., filter cassette or sorbent tube), and a calibrated primary standard. The sampling media should be the same type used during actual air sampling to account for any backpressure effects. Next, the pump is connected to the primary standard, and the flow rate is measured. This measurement is typically done before and after each sampling period to check for any drift in the pump's flow rate. The flow rate is adjusted, if necessary, using the pump's adjustment knob until it matches the desired flow rate specified by the sampling method. The desired flow rate depends on the contaminant being sampled and the sampling media used. The calibration must be performed with the sampling train assembled as it would be during actual sampling, as the resistance of the sampling media affects the flow rate. Record the initial flow rate, final flow rate, date, time, and the name of the person performing the calibration. If the flow rate changes by more than 5% during the sampling period, the sample may be invalid. For example, if you are sampling for silica dust using a filter cassette that requires a flow rate of 2 liters per minute (LPM), you would connect the pump and cassette to a calibrated rotameter or electronic calibrator, adjust the pump until the flow rate is 2 LPM, and record the flow rate. You would then repeat this process after the sampling period to ensure the flow rate remained consistent. Regular calibration, at least annually and after any repairs, is critical for maintaining the accuracy of air sampling data.