Expired or previously used and sterilized N95 respirators can be used when new N95 respirators are unavailable during the coronavirus disease 2019 (COVID-19) pandemic, according to the results of a quality improvement study published in JAMA Internal Medicine.

Researchers conducted fitted filtration efficiency (FFE) tests on 29 different respirators and face masks between April and June 2020 in a custom-built exposure chamber. They measured FFE during a series of repeated movements of the torso, head, and facial muscles to simulate typical physical activities of a mask wearer. A Particle Generator 8026 supplemented ambient particle counts, and the particle concentration was allowed to stabilize for 30 minutes before testing. The temperature ranged between 23 oC and 29.5 oC and the relative humidity was between 10% and 50%.

The following sterilization methods were tested on used masks: ethylene oxide (500 mg/L-hours at 50 oC, 16-hour cycle), steam (121 oC, 15 minutes), and vaporized hydrogen peroxide (8 g/min, 260 PPM, 100-minute cycle).

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The N95 respirators that expired up to 11 years past their expiration date (2009 and 2011) and the N95 respirators sterilized using the ethylene oxide and vaporized hydrogen peroxide methods retained their FFEs >95%. Steaming visibly distorted the 1860 N95 respirators, which made them unusable. The 1870+ Aura face masks, however, were not visibly altered and maintained >95% FFE after a single cycle of steam autoclaving.

Although N95 respirators with exhalation valves are not generally used in healthcare settings because of the expired air, the researchers noted that the FFE of those masks was also >95%. However, N95 respirators in the wrong size had decreased FFEs between 90% and 95%.

Both surgical and procedure masks had substantially lower average FFEs than N95 respirators, as expected, and the variability was largely dependent upon the tightness between the individual’s skin and mask material. Interestingly, FFE of masks with ties outperformed masks with ear loops. This suggests that the elastic ear loops may not provide sufficient tension to maintain a secure fit during a typical range of motions.

A major limitation of this study was that the researchers tested each mask on only 1 man and 1 woman vs a large number of individuals.

“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,” the researchers concluded.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Sickbert-Bennett EE, Samet JM, Clapp PW, et al. Filtration efficiency of hospital face mask alternatives available for use during the COVID-10 pandemic. JAMA Intern Med. Published online August 11, 2020. doi:10.1001/jamainternmed.2020.4221

This article originally appeared on Pulmonology Advisor