During the COVID-19 pandemic, widespread shortages of filtering facepiece respirators have prompted the use of nonstandard practices to provide protection for health care workers. Researchers compared the fitted filtration efficiencies of 29 respirators and face masks used in health care facilities, including expired N95 respirators, sterilized N95 respirators, Centers for Disease Control and Prevention (CDC)-approved imported respirators, respirators not listed as approved, and surgical or procedural masks with ties or ear loops.

The masks were fitted on one male and one female volunteer and tested in a custom-built exposure chamber in which ambient particles were supplemented with sodium chloride particles. Fitted filtration efficiency was measured during a series of repeated movements of the torso, head, and facial muscles to simulate typical occupational activities.

N95 respirators up to 11 years past expiration with intact elastic bands and N95 respirators subjected to ethylene oxide and vaporized hydrogen peroxide sterilization retained more than 95% fitted filtration efficiencies. The respirators that are not listed as approved and the two imported respirators that are approved by the CDC but don't meet National Institute for Occupational Safety and Health standards did not achieve 95% fitted filtration efficiencies. Compared with N95 respirators, surgical and procedural masks had substantially lower fitted filtration efficiencies. In all tests, masks with ties were more efficient than those with ear loops. Wearing N95 respirators in the wrong size led to decreased fitted filtration efficiencies, the authors observed, while noting that these respirators were still more than 90% efficient.

A limitation of the study was that masks were tested on just one man and one woman.