Negative pressure and aerosol systems for fit testing of respirators on human subjects were compared. Subjects wore small, medium, or large size half mask or full facepiece probed respirators for the conducting of fit tests. By removing the cartridges and installing airtight manifolds in the cartridge receptacles, negative pressure tests were accomplished. Repeated sequential fit tests were conducted on a single subject using both fit test systems. Repeated testing was conducted on three subjects over a 1 month period with both half mask and full face respirators. Sequential fit tests were conducted for 125 military and civilian workers in a respiratory protection program using both negative pressure and aerosol tests. The controlled negative pressure system consistently detected a range of air leakage through fixed leaks and respirator face seals. The aerosol system results were in general an order of magnitude lower than those determined by the negative pressure tests. An assumed inspiratory flow of 431 milliliters/second was used to calculate the negative pressure determined fit factors. Relatively low levels of challenge aerosol were detected in the mask sampling line. The authors suggest that other factors such as leak penetration losses, incomplete mixing due to streamlining, and lung retention may have been important contributors to the reduced aerosol levels detected. The authors conclude that the aerosol fit test systems may seriously underestimate air leakage into respirators.
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