Sampling Pump Flow Rate
Sampling pump flow rate is the volume of air per unit time drawn through a sampling train during air monitoring, expressed in litres per minute (L/min) for particulates or millilitres per minute (mL/min) for gases and vapours. It must be known, specific, and stable, typically within ±5% of the target, to accurately calculate sampled air volume and worker exposure concentration per NIOSH, OSHA, and ASTM methods.
On a shop floor, sampling pump flow rate is critical for personal and area air monitoring to comply with exposure limits. For particulates like welding fume or silica, flow rates of 1–5 L/min are used through filters and cyclones; for gases and vapours like solvents, 20–500 mL/min through sorbent tubes. Technicians set and verify flow pre- and post-sampling using calibrated standards, ensuring the average flow is within ±5% of the target. The sampled volume is calculated as average flow times sampling time, and deviations beyond ±5% may invalidate the sample. WorkSafeBC and OSHA expect documented pre-/post-flow checks and traceable calibrations.
How is sampling pump flow rate linked mathematically to exposure concentration?
Airborne concentration C is calculated as C = m / V, where m is the mass of contaminant collected and V is the sampled air volume. Volume V is derived from the pump flow rate: V = Q_avg × t, where Q_avg is the average of initial and final flow rates (L/min) and t is sampling time (min). A 10% error in Q_avg yields roughly a 10% error in calculated concentration, hence the ±5% flow stability criterion.
What are recognized tolerances for flow rate calibration and stability?
Common criteria include at least three flow readings agreeing within ±2–5% for calibration, and final flow within ±5% of initial for sample acceptability. Some procedures use the lower flow if difference is >5% but ≤10%, and void the sample if >10%. For regulated applications like coal mine dust, flow must not vary by more than ±0.1 L/min over 10 hours at 2 L/min.
How do I choose flow rate for a new sampling project in a BC facility?
Identify the contaminant and applicable WorkSafeBC OELs, then select an approved NIOSH or OSHA method specifying the sampler type and flow rate. Set the pump to match that flow, verify pump capability (flow range, battery life), and calibrate with documented pre- and post-sampling flows using accepted practices.