Mask Filtration Efficiency

Angie Szumlinski Health, Studies

In March 2020, the soaring number of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections resulted in an unprecedented shortage of personal protective equipment (PPE) for clinicians and essential health care workers. The shortage was most profound among N95 respirators, named for their ability to filter 95% or more of tiny 0.3 µm particles, and are considered the mainstay of protection against airborne pathogens. To mitigate the shortage of N95 respirators, many health care facilities are pursuing non-standard approaches to maintaining an adequate supply, including mask decontamination and reprocessing for reused, which extend the wearable life of the mask beyond the expiration date and procuring KN95 masks (N95 masks that are regulated in China).

A recent laboratory-based evaluation of a broad array of non-standard face masks demonstrated that the National Institute for Occupational Safety and Health (NIOSH)-approved N95 respirators outperform alternatives in terms of filtration efficiency. Results of the study demonstrated that N95 masks reprocessed using ethylene oxide sterilization as well as masks that are up to 11 years past expiration, maintain very high filtration efficiency under laboratory conditions. N95 masks with suboptimal fit still had comparable filtration efficiency of more than 90%. The KN95 masks however performed less well, with filtration efficiency ranging from 53% to 85%. Surgical masks, secured with either ties or ear loops also had much lower filtration efficiency of 37% to 69%, as might be expected by their more comfortable, thinner filter and looser fit.

Frontline clinicians and essential health care works who engage in the highest risk procedures should be afforded the highest level of protection with NIOSH-approved N95 respirators. The study demonstrates that the reprocessed use and expired supply of N95 masks are safe and offer excellent alternatives to standard, single-use N95 masks. Despite lower filtration efficiencies of submicron particles, surgical masks, and other N95 alternatives likely provide adequate protection against transmission for routine care. Stay the course, stay strong, stay well, mask up and stay tuned!