The effect of pressure drop on respirator faceseal leakage.

Users of particulate air-purifying respirators are typically told to change their filters when breathing resistance becomes uncomfortable. It has been proposed that a noticeable increase in breathing resistance (pressure drop) may increase airflow through respirator faceseal leaks. This logic has been extended to suggest that respirator user exposure to contaminants may increase because of this theoretical increase in air leakage. Procedures similar to those of previous investigators were used to study this issue. Repeated faceseal leak rate measurements were made at -5.6 through -20.1 mm water pressure drops across the faceseal. Subjects were divided into two groups, representing acceptable fit or unacceptable fit, based on leak rate criteria prescribed by the Occupational Safety and Health Administration (OSHA). Subjects with acceptable fit did not experience an increase in faceseal leak rate with increased pressure drop. Leak rates for subjects with unacceptable fit were highly variable and did not show an association with pressure drop. Results of this study do not support the concept of increased faceseal leakage with increased pressure drop. The evidence does not suggest increased risk of contaminant exposure through the face seal as pressure drop increases.