Efficiency and Pressure Drop Effects of High Concentrations of Cement Dust on N95 Electret Filters

ield tests were conducted to measure the effects of high concentrations of cement dust on the penetration and pressure drop of N95 electret respirator filters from two manufacturers. Three groups of each manufacturer’s filter were tested: 1) untreated; 2) irradiated with ionizing radiation; 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 “worst-case” NIOSH test conditions. Laboratory initial penetration values for the treated filters ranged from approximately 7% to 60% when tested using the NIOSH test procedures. The filters were then exposed to high concentrations of cement dust in a concrete block manufacturing plant. Dust loading on individual filters ranged from approximately 12 mg to 91 mg; mean dust loading by group was in the range of 31 to 40 mg. There was no significant difference in mean cement dust penetration among the three treatments for one manufacturer’s filters. Cement dust penetrations for the second manufacturer’s filter groups were statistically different from one another, but the highest mean penetration was only 0.228%. The workplace loading had minimal effect on pressure drop measurements. Laboratory aerosol penetration increased slightly for the untreated filters from both manufacturers, caused by masking of electrical charges on the media. Post-workplace laboratory penetration for the irradiated and IPA dipped filters from both manufacturers decreased significantly. This indicates improved mechanical efficiency with dust loading. These findings are consistent with predictions of filter performance modeling. As expected, current NIOSH approved N95 filters perform very well in very dusty conditions. Under the conditions of this study, filters with laboratory penetration values far in excess of those permitted for NIOSH approval were still very efficient in this workplace. This study provides additional assurance that users of currently approved N95 filters will not lose protection if some charge loss should occur in the workplace.