The effect of respirator dead space and lung retention on exposure estimates.
Am Ind Hyg Assoc J 1993 Dec; 54(12):711-722
The effects of respirator dead space and lung retention on inhalation exposure estimates were examined. Equations expressing the effects of respirator dead space and lung retention on inhalation, exhalation, and full cycle equilibrium average contaminant concentrations inside a respirator were derived for filter penetration and face seal leakage or no filter penetration and face seal leakage. The equations were based on mass transfer relations and assumed that air entering the filters was mixed with exhaled air or not mixed (plug flow condition). For a dead space volume of zero, no mixing was predicted to occur and the difference between the inhaled and exhaled contaminant concentrations was maximal. For nonzero dead space volumes, the difference between the inhaled and exhaled concentrations decreased with increasing volume. The presence of a face seal leak resulted in a higher average in/respirator contaminant concentration than the no leakage condition. During the plug flow condition, a greater proportion of the contaminant could enter the mask, but was not inhaled, and consequently would not be retained in the respiratory tract. The validity of the equations was evaluated by comparing their predicted average concentrations with concentrations measured during a laboratory simulation. A mannequin fitted with a quarter, half, or full face respirator was connected to a breathing machine. Dead space volumes of 0.14 to 1.73 times the respirator volume were used. Polydisperse and monodisperse aerosols of oleic-acid tagged with uranine dye were used as the test aerosol. Concentrations predicted for good mixing of inhaled and exhaled air showed the best agreement with the experimental values. Concentrations predicted for the plug flow condition showed the worst agreement. The dead spaces reduced the average in/respirator aerosol concentrations by up to 50%. The authors conclude that respirator dead space and lung retention can reduce average inhaled contaminant concentrations in a respirator by as much as 50%. The effect increases with increasing head space volume. Areas in which the equations can be applied are discussed, including fit factor evaluations, respirator performance modeling, and workplace protection factor studies.
NIOSH-Publication; NIOSH-Grant; Respirators; Training; Respiratory-protective-equipment; Industrial-hygiene; Equipment-reliability; Mathematical-models; Laboratory-testing; Occupational-exposure
Inst of Safety & Systems Mgmt University of California University Park Los Angeles, Calif 90089-0021
American Industrial Hygiene Association Journal
University of Southern California, Los Angeles, California