Relative survival of Bacillus subtilis spores loaded on filtering facepiece respirators after five decontamination methods

This study determines the relative survival ( RS ) of Bacillus subtilis spores loaded on an N95 filtering facepiece respirator ( FFR ) after decontamination by five methods under worst‐case conditions. Relative survival was obtained by testing after decontamination and after storing the FFR s at 37°C and 95% relative humidity for 24 hours. The decontamination methods involved ethanol, bleach, ultraviolet irradiation ( UVA 365 nm, UVC 254 nm), an autoclave, and a traditional electric rice cooker ( TERC ) that was made in Taiwan. Without decontamination, 59 ± 8% of the loaded spores survived for 24 hours. When 70% ethanol was added to the N95 FFR at a packing density of 0.23, the RS was 73 ± 5% initially and decayed to 22 ± 8% in 24 hours. Relative survival remained above 20% after 20 minutes of UVA irradiation. The other four decontamination measures achieved 99%‐100% biocidal efficacy, as measured immediately after the methods were applied to the test FFR s. Relative survival is a useful parameter for measuring sterilization or degree of disinfection. Bleach, UVC , an autoclave, and a TERC provide better biocidal efficacy than ethanol and UVA . Not only a higher filter quality but also a lower value of RS produced the most decontaminated FFR .