Study: Wearing surgical masks over N95s can cause dangerous leaks

Healthcare worker wearing a medical mask on top of a respirator

Hospital CLINIC / Flickr cc

For optimal protection against respiratory pathogens such as SARS-CoV-2, procedure masks shouldn't be worn over N95 filtering facepiece respirators (FFRs), according to a study published today in Infection Control & Hospital Epidemiology.

The National Institute for Occupational Safety and Health (NIOSH), part of the Centers for Disease Control and Prevention, does not recommend wearing a mask over a respirator. In a June 2020 agency blog post, NIOSH researchers said, "Wearing a surgical mask or cloth covering over an FFR, such as an N95, is not approved or recommended by NIOSH because it is not consistent with the conditions of the approval, therefore voiding the certification."

But they add, "However, this is a strategy that can be used in a crisis situation" to prolong FFR use when they are in short supply.

Increased pressures can cause leakage

Researchers from Mayo Clinic in Phoenix and the University of Tulsa noted that the need to conserve/reuse N95 FFRs early in the COVID-19 pandemic led public health agencies and associations to say that cloths or procedure/surgical masks can be worn over N95s to prevent or reduce FFR microbial contamination.

"Although this idea is intuitively appealing, we found no published evidence demonstrating this presumed benefit," they wrote.

The team studied N95 respiratory performance in 100 healthcare workers who had successfully completed Accufit Pro 9000 quantitative fit-testing with Mayo Clinic occupational health staff wearing a 3M 1870+ Aura FFR. But when they added a Halyard 47117 procedure mask over the same N95, 13% failed fit-testing.

"The additional resistance created by an overlying face mask can lead to increased airway pressures that cause leakage at the N95 FFR facial seal," the authors wrote.

An avoidable risk

Disposable N95 FFRs are designed, regulated, and marketed for single use and carry the warning, "Fit testing must be performed while the test subject is wearing any applicable safety equipment that may be worn during actual respirator use which could interfere with respirator fit."

That statement, the researchers said, indicates than an N95 fit-testing result is valid only for the conditions at testing. "Thus, adding an overlying face mask later invalidates test results obtained when the overlying face mask was not in place," they wrote.

The additional resistance created by an overlying face mask can lead to increased airway pressures that cause leakage

The team cautioned that their results may not apply to other combinations of N95s and face masks but said that generic guidance on the use of N95s should consider the possible risk of failure when they are worn beneath a procedure mask.

"Because N95 FFRs are often worn in high-burden environments (eg, during aerosolizing procedures), N95 FFR failure may result in significant health consequences," they concluded. "Given both community and healthcare use of N95 FFRs, it is imperative that this avoidable risk be recognized and understood."

This week's top reads