Collection efficiencies of airpurifying respirators containing electrostatic filter media

Abstract

Electrostatic media are widely used in particulate air purifying cartridges and filtering facepiece respirators. Such media provides high collection efficiency while affording low breathing resistance to the wearer. The certification method used by National Institute for Occupational Safety and Health (NIOSH) is considered to represent worse case respirator performance. Respirator certification does not consider either the mechanism of particle capture or the type of filter media used in a respirator. The correlation between respirator penetration with particles less than 1 μm for predicting worker exposure to air contaminants greater than 1 μm has not been validated. This research was undertaken to: 1) evaluate the collection efficiency of particulate air purifying respirators containing electrostatic filter media and 2) determine if the NIOSH method used for respirator certification accurately predicts collection efficiency of these respirators loaded with contaminants representative of the workplace. Two of the three contaminants selected for this project, asphalt fumes and synthetic metal cutting fluid mist, possess chemical and/or physical properties in addition to a vapor stage that could mask or degrade the charge on the electrostatic fibers. The third workplace aerosol, aluminum oxide dust, was selected to be representative of a solid particulate mineral dust. Filtering facepiece respirators are often used in environments where they become saturated with the wearer's perspiration. Perspiration contains ions that could interact with the charge on an electrostatic filter. Affect on collection efficiency was determined after a respirator saturated with artificial perspiration was dried with HEPA filtered air. The findings of this work support the following conclusions: 1) the NIOSH method test for N95 respirators underestimates penetration of respirators loaded with laboratory and field generated workplace contaminants, 2) N95 respirators containing electrostatic filter media did not perform significantly different from an N95 mechanical filter media respirator, 3) penetration of some N95 respirators fully loaded with either asphalt contaminants or synthetic metal cutting fluid mist increased beyond the rating of the respirator, and 4) performance of filtering facepiece respirators saturated in artificial perspiration were not significantly affected after the respirators were dried.