N95 respirators can be safely decontaminated without undermining functional integrity only two or three times, a government study showed.
Both ultraviolet light and vaporized hydrogen peroxide met the bar for killing off SARS-CoV-2 virus that causes COVID-19 without impacting fit testing for two rounds of wear and decontamination compared with control respirators. Filtration remained “acceptable” after a third round for those two methods as well.
Vaporized hydrogen peroxide (VHP, approximately 1,000 ppm) was the faster of the two, reported Vincent Munster, PhD, chief of the National Institute of Allergy and Infectious Diseases’ Virus Ecology Unit in Hamilton, Montana, and colleagues.
VHP eliminated viral growth in media exposed to the mask after decontamination to zero in about 10 minutes, whereas ultraviolet light (260-285 nm) dropped it to below the acceptable level in about an hour.
“Taken together, our findings show that VHP treatment exhibits the best combination of rapid inactivation of SARS-CoV-2 and preservation of N95 respirator integrity, under the experimental conditions used here,” they wrote in a study on the preprint server medRxiv.
Preprint studies have not been peer-reviewed and should not be used to guide clinical practice, according to the site.
The CDC has not approved any method for decontaminating masks, but it has said it “does not intend to object to the distribution and use of sterilizers, disinfectant devices, and air purifiers that are intended to be effective at killing SARS-CoV-2 … FDA believes such devices will not create such an undue risk, when performance and labeling criteria are met.”
The study also looked at a 70% ethanol solution sprayed to saturation and heat treatment in a 70°C (158°F) oven for 10 minutes.
Ethanol was quick to decontaminate the respirators but didn’t pass the test for respirator function on the second round of decontamination.
Dry heat was slow, taking about an hour to hit the viral kill threshold, but kept proper function for two rounds of decontamination.
The researchers cautioned that how contaminated masks are initially will impact how long they need to be treated for, particularly with ultraviolet light and dry heat. Also, “utmost care should be given to ensure the proper functioning of the N95 respirator after each decontamination using readily available qualitative fit testing tools,” Munster’s group wrote.
A separate group studying N95 respirator decontamination has cautioned that soapy water, alcohol, bleach immersion, and overnight storage are unsuitable.