Aerodynamics and exposure variability.
Appl Occup Environ Hyg 1991 Jan; 6(1):36-39
Factors affecting variability in determinations of time weighted average (TWA) breathing zone exposures in the workplace were examined. The theoretical aspects of exposure variance were discussed. Wind tunnel studies to examine the influence of contaminant generation rate and the relative location of the source and worker were conducted with a department store manikin and sulfur- hexafluoride tracer gas. The tracer source was positioned at distances of 3.0 to 10.0 inches from the manikin along a line perpendicular to the torso at a chest height of 2.25 feet. The manikin and tracer source were positioned so that the air flow was parallel to both or the source was positioned downstream from the manikin. Air flow velocities were 49, 152, or 265 feet per minute. Breathing zone concentrations were measured with an infrared spectrophotometer and recorded with a data logger to produce 10 minute TWA exposures. The degree of variance in the TWA data was determined by various statistical techniques. The variance was one to two orders of magnitude greater when the sulfur-hexafluoride source was located downstream from the manikin compared to the parallel airflow position. The authors conclude that the increased variance resulting from placing the source downstream from the manikin is due to the source being in a separated boundary layer. The boundary layer effect is more important than the actual air velocity and source to breathing zone distance. The data should be useful in assisting industrial hygienists to identify situations of high exposure variability.
NIOSH-Publication; NIOSH-Grant; Industrial-hygiene; Air-flow; Occupational-exposure; Air-sampling; Time-weighted-average-exposure; Simulation-methods; Laboratory-testing; Laboratory-techniques
Environmental Sciences & Engr University of North Carolina Rosenau Hall 201H Chapel Hill, NC 27514
Applied Occupational and Environmental Hygiene
University of North Carolina Chapel Hill, Chapel Hill, North Carolina