Filter quality of electret masks in filtering 14.6–594 nm aerosol particles: Effects of five decontamination methods

<div><p>This study investigates the effects of five decontamination methods on the filter quality (<i>q</i>_<i>f</i>) of three commercially available electret masks—N95, Gauze and Spunlace nonwoven masks. Newly developed evaluation methods, the overall filter quality (<i>q</i>_{<i>f</i>,<i>o</i>}) and the <i>q</i>_<i>f</i> ratio were applied to evaluate the effectiveness of decontamination methods for respirators. A scanning mobility particle sizer is utilized to measure the concentration of polydispersed particles with diameter 14.6–594 nm. The penetration of particles and pressure drop (Δ<i>p</i>) through the mask are used to determine <i>q</i>_<i>f</i> and <i>q</i>_{<i>f</i>,<i>o</i>}. Experimental results reveal that the most penetrating particle size (MPS) for the pre-decontaminated N95, Gauze and Spunlace masks were 118 nm, 461 nm and 279 nm, respectively, and the respective penetration rates were 2.6%, 23.2% and 70.0%. The Δ<i>p</i> through the pretreated N95 masks was 9.2 mm H₂O at the breathing flow rate of heavy-duty workers, exceeding the Δ<i>p</i> values obtained through Gauze and Spunlace masks. Decontamination increased the sizes of the most penetrating particles, changing the <i>q</i>_<i>f</i> values of all of the masks: <i>q</i>_<i>f</i> fell as particle size increased because the penetration increased. Bleach increased the Δ<i>p</i> of N95, but destroyed the Gauze mask. However, the use of an autoclave reduces the Δ<i>p</i> values of both the N95 and the Gauze mask. Neither the rice cooker nor ethanol altered the Δ<i>p</i> of the Gauze mask. Chemical decontamination methods reduced the <i>q</i>_{<i>f</i>,<i>o</i>} values for the three electret masks. The value of <i>q</i>_{<i>f</i>,<i>o</i>} for PM_0.1 exceeded that for PM_0.1–0.6, because particles smaller than 100 nm had lower penetration, resulting in a better <i>q</i>_<i>f</i> for a given pressure drop. The values of <i>q</i>_{<i>f</i>,<i>o</i>}, particularly for PM_0.1, reveal that for the tested treatments and masks, physical decontamination methods are less destructive to the filter than chemical methods. Nevertheless, when purchasing new or reusing FFRs, penetration should be regarded as the priority.</p>