Diffusion effects under low flow conditions.
Am Ind Hyg Assoc J 1983; 44(6):453-462
Low and high flow rate personal sampling pumps were compared for diffusion effects. Tests were run to determine at what flow rate positive bias occurs as a result of diffusive mass influx at the solid sorbent tube sampling train inlet. Two mathematical models predicted the flow rate at which diffusive flux is a bias. Less than 3.0 cubic centimeters per minute (cc/min) and 1.5cc/min were the flow rates where bias was predicted. To test these mathematical models, experimental tests were performed. Two sets of ethanol (64175) samples were collected on charcoal tubes, one set at monitored ethanol concentration in the test manifold. To measure volumetric flow rates, the rate of pressure increase was determined using a transducer and valving. Ethanol samples were taken and analyzed by gas chromatography. Analysis of samples collected at flow rates of 0.8cc/min showed concentrations as much as 75 percent higher than from samples collected at flow rates of 20cc/min. The author concludes that diffusive flux can be a bias at low sampling.
NIOSH-Author; Diffusion-analysis; Analytical-methods; Industrial-hygiene; Industrial-environment; Atmosphere-analyzers; Monitoring-systems; Air-monitoring; Sandblasting; Air-sampling-techniques
William A. Heitbrink, U.S. Department of Health & Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety & Health, 4676 Columbia Parkway, Cincinnati, OH 45226
American Industrial Hygiene Association Journal