Efficiency of Degraded Electret Filters: Part I – Laboratory Testing Against NaCl and DOP before and after Exposure to Workplace Aerosols

Laboratory studies have demonstrated degradation of electrostatically-enhanced (electret) respirator filter performance after exposure to excessive levels of ionizing radiation, immersion in solvents, and when exposed intermittently to specific aerosols. This study was conducted to determine if such degradation has practical significance in the workplace. N95, R or P95 and P100 filters from two manufacturers were tested. All filters were electrets except the P100 filters from one manufacturer. Each filter type was divided into three groups: 1) untreated; 2) irradiated with ionizing radiation; and 3) dipped in isopropanol for 15 seconds. The purpose of the irradiation and isopropanol treatments was to produce laboratory penetration values above those allowed for approval using NIOSH test conditions. Initial penetration and pressure drop measurements were made with an automated filter tester (AFT) using sodium chloride for N filters and DOP for R and P filters. Filters from each group were then exposed to a grinding aerosol or an oil mist in a steel foundry. Following the workplace exposure, the filters and controls for each group were retested for initial penetration and pressure drop. Results of the AFT testing did not indicate changes in penetration or pressure drop attributable to the workplace aerosols.