Comparison of Mask Types Finds Key Differences in Filtration

Megan Brooks

August 11, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

N95 masks that are well past their expiration date or have been used and re-sterilized are acceptable alternatives to standard new single-use N95 masks, new research indicates. But some masks start off with better filtration efficiency than others.

Personal protective equipment (PPE) and especially N95 respirators — named for their ability to filter 95% or more of tiny 0.3-μm particles — are scarce commodities in the time of COVID-19.

Shortages in PPE and N95 masks have led some providers and health systems to get creative, adopting nonstandard practices such as using expired N95 masks and various decontamination processes to prolong their use. Hospitals are also turning to imported or donated masks that are not approved by the National Institute for Occupational Safety and Health (NIOSH) as a potential replacement for limited NIOSH-approved N95 masks.

But how safe and effective are these alternatives? A new study published online today in JAMA Internal Medicine provides some reassuring data.

Emily Sickbert-Bennett, PhD, with the Infection Prevention Department, University of North Carolina Health Care, Chapel Hill, and colleagues tested the fitted filtration efficiencies (FFEs) of 29 different fitted face mask alternatives worn by a male and female volunteer in a custom-built exposure chamber. 

They measured FFEs during a series of repeated movements of the torso, head, and facial muscles to recreate typical occupational activities of the mask wearer. They used a particle generator to supplement ambient particle counts in the chamber.

According to Sickbert-Bennett and colleagues, N95 respirators up to 11 years past their expiration date with intact elastic straps and those that had been sterilized with ethylene oxide and hydrogen peroxide retained FFEs > 95%.

The performance of N95 masks in the wrong size was slightly lower, with FFEs between 90% and 95%.

The researchers also evaluated steam sterilization for two respirator models. Steam visibly distorted the 3M 1860 N95 respirators, rendering them "unsuitable" for reuse. However, the 3M 1870+ Aura face masks were not visibly altered and maintained > 95% FFE when put through a single cycle of steam autoclaving, they report.

All six of the respirators not listed as approved failed to achieve 95% FFE. They are the SAS Safety Corp 8617 Duckbill; Fangtian Duckbill FT-032 with exhaust valve; Safe Life N95 B150; Jia Hu Kang KN95 mask with ear loops; Zhongshan Dongfeng Huangshang GM700; and Guangdong Fei Fan KN95.

In addition, neither of the two imported respirators approved by the US Centers for Disease Control and Prevention but not by NIOSH (Dasheng DTC-3X-1 and DTC-3X-2) achieved 95% FFE; DTC-3X-1 was the more effective of the two (approximately 80% FFE).

"These respirators, which have elastic ear loops and a vertical fold design, were least effective when the test individual bent at the waist and looked up and down," say the researchers.  

Surgical, Procedure Masks Likely Okay in Routine Care

Not surprisingly, surgical and procedure masks had substantially lower average FFEs than the N95 respirators, they found. The variability in their performances was largely dependent on the tightness of the contact between the material and the wearer's skin.

In all tests, the FFE of masks secured with ties outperformed those secured with ear loops, researchers say.

Procedure masks with ear loops had FFEs of only 38.1%. They were least effective when the wearer's head moved from left and right (21.2% FFE), and created visible gaps between the face mask and the wearer.

"Taken together, these data suggest that elastic ear loops may not provide adequate tension to maintain a tight fit during a typical range of motions. Moreover, these findings illustrate the importance of fit for maximizing the overall effectiveness of both respirators and masks," the researchers write.

"This evaluation provides quantitative results on which health care administrators, supply chain leaders, and hospital epidemiologists can make evidence-based decisions to protect clinicians and other health care workers during a pandemic or long-term mask shortage," Sickbert-Bennett and colleagues conclude.

The coauthors of a linked editorial say despite the apparent "imperfect" FFE of non-NIOSH approved respirators and surgical masks in the laboratory, "there is reason for optimism regarding their real-world effectiveness."

It is "critically important" to find innovative ways to overcome PPE shortages, write Caitlin Dugdale, MD, and Rochelle Walensky, MD, MPH, from Massachusetts General Hospital, Boston.

"Frontline clinicians and essential health care workers who engage in the highest risk procedures should be afforded the highest level of protection with NIOSH-approved N95 respirators," they point out.

The current study shows that 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."

This study was supported by a cooperative agreement between the University of North Carolina at Chapel Hill and the US Environmental Protection Agency. Sickbert-Bennett has reported receiving consultation fees from PDI and Johnson & Johnson. Dugdale has reported receiving travel reimbursement from the Infectious Diseases Society of America and personal fees from the Joint United Nations Programme on HIV/AIDS.

JAMA Intern Med. Published online August  11, 2020. Full text, Editorial

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