Filter Performance Degradation of Electrostatic N95 and P100 Filtering Facepiece Respirators by Dioctyl Phthalate Aerosol Loading

Polydisperse dioctyl phthalate (DOP) aerosols are employed for testing filter penetration with loading of Rand P-series particulate filters for National Institute for Occupational Safety and Health (NIOSH) certification. Penetration for filters must not exceed NIOSH allowed maximum levels during the entire loading of 200 mg DOP indicating no filter degradation. Degradation of respirators loaded with DOP by other aerosols as well as respirators exposed to both oil and non-oil aerosols found in some workplaces is not well studied. To better understand the degradation of respirators with electrostatic filter media, two models of N95 and P100 filtering facepiece respirators (FFRs) were loaded with polydisperse DOP aerosols up to 200 mg as employed for NIOSH certification testing with simultaneous measurement of filter penetration. In parallel experiments, both N95 and P100 FFRs were loaded with 10 to 200 mg DOP and challenged with polydisperse NaCl aerosol employed for NIOSH certification testing as well as monodisperse NaCl aerosol, and filter penetration was measured. Results showed that filter penetration for both N95 models increased with increasing amounts of DOP loading and exceeded NIOSH allowed maximum penetration (5%) by both DOP and NaCl aerosols indicating filter degradation. Monodisperse NaCl aerosols (20-400 nm) gradually increased the penetration and shifted the most penetrating particle size from ~40 nm to larger sizes. In the case of P100 FFRs, DOP aerosol penetration was below 0.03% for up to 200 mg DOP loading as required for NIOSH certification. Interestingly, one of the two P100 FFR models loaded with 10-50 mg DOP showed >0.03% penetration with polydisperse, as well as monodisperse, NaCl aerosol testing. Overall, the results obtained in the study indicate that some P100 models loaded with DOP at lower amounts may show higher penetration with other aerosols such as NaCl. Further studies are needed to better understand the filter degradation of DOP loaded respirators. INTRODUCTION The National Institute for Occupational Safety and Health (NIOSH) recommends the use of particulate respirators for protection against airborne inert and biological particles in many workplaces. NIOSH approves three categories, N (not resistant to oil), R (resistant to oil), and P (oil proof) of particulate filters based on resistance to filter efficiency degradation by dioctyl phthalate (DOP) [1]. Each category of filter is certified at three levels of filter efficiency 95%, 99%, and 99.97%, designated as class 95, class 99 and class 100, respectively. For example, a filter marked N100 would mean an Nseries filter that is at least 99.97% efficient. The filtration efficiency of respirators is measured using a more challenging test method with charge neutralized aerosol particles at 85 L/min flow rate. To measure the filter efficiency degradation, filtering facepiece respirators (FFRs) are loaded with test aerosols, up to 200 mg, with a simultaneous filter penetration measurement. The maximum penetration must not exceed 5%, 1% and 0.03% for class 95, 99 and 100 FFRs, respectively, during the entire loading period of 200 mg test aerosols [1]. For certification of Rand Pdesignated respirators, polydisperse DOP aerosol with a count median diameter (CMD) of 185 ± 20 nm and a geometric standard deviation (GSD) of less than 1.60 is used. DOP aerosol is known to degrade N-series respirators and increase filter penetration. For this reason, N-series respirators are tested using polydisperse NaCl aerosols with a CMD of 75 ± 20 nm and a GSD of less than 1.86.