Still in short supply in Minnesota, N95 masks used over and over

Three months into the COVID-19 pandemic, nurses and other clinicians are being forced to reuse hospital masks in ways that would have gotten them written up a year ago, according to the Minneapolis Tribune.

Maplewood-based mask-maker 3M Co. said Friday that despite doubling its production of N95 respirators this year, global demand continues to far exceed the supply for the entire industry. With too few respirators to go around, hospital administrators are left to decide how best to protect their staffs, even as some evidence suggests health care workers are transmitting the virus among themselves while at work.

Contract tracing shows 4% of health care workers in Minnesota who have unprotected exposure to COVID-positive co-workers test positive within 14 days, though it’s not possible to rule out community transmission. All told, health care workers, including hospital staff, make up about 10% of Minnesota’s 35,549 lab-confirmed cases.

Tight-fitting N95 masks — designed to protect the wearer by trapping 95% of particles of a specific tiny size — are in such demand that hospitals are doing everything they can to extend a mask’s life, from storing them in paper bags hanging on the wall to using UV light and hydrogen peroxide to clean and disinfect them.

Rather than using and discarding several N95s per day, a common practice before the pandemic, nurses and other clinicians now wear a single mask for an 8-hour shift or longer. That mask is then used again for up to five nonconsecutive shifts, hospitals and nurses say.

After that, the masks are often put in storage in preparation for a future surge.

To kill the virus, some hospitals are using machines that zap the masks with ultraviolet light, or bathe them in vaporized hydrogen peroxide. A more common strategy, described in guidance from the Centers for Disease Control and Prevention, is to put used masks in separate paper bags where they can air out until any virus dies.

N95s protect the wearer, while looser-fitting surgical masks and cloth masks worn in public protect the people around them by blocking microscopic droplets in their breath that can spread the virus. In hospitals and clinics, health care providers sometimes wear surgical masks or full face shields over their N95s to preserve the mask.

In the government recommendations, mask decontamination is depicted as a strategy of last resort.

Guidelines from the CDC urge a wait-and-reuse approach before considering disinfecting. The CDC says respirators from other countries may be considered, though the Food and Drug Administration has said certain masks made overseas are no longer authorized for distribution in the U.S.

OSHA says decontamination voids the approval granted by the CDC’s National Institute for Occupational Safety and Health (NIOSH).

“Still, during periods of shortages … when other preferred alternative respirators … are not available, filtering facepiece respirator decontamination and reuse may need to be considered as a crisis capacity strategy,” the OSHA guidelines say.

NIOSH says three methods offer the “most promise” for cleansing and purifying N95 masks: vaporous hydrogen peroxide (VHP), ultraviolet (UV) radiation, and “moist heat” from water heated in an oven.

Methods that NIOSH said should be avoided, because they damage the mask, include dry heat, 70% isopropyl alcohol and microwave irradiation.

Federally funded study results published this month in the CDC journal Emerging Infectious Diseases noted that using VHP resulted in the best combination of rapid decontamination and least damage to the mask. UV light killed the virus more slowly, the study said, but preserved mask function “almost as well.”

The study, using 3M’s Aura N95 respirators, concluded that the masks can be reused up to three times after being treated with UV or VHP.

3M does not recommend decontaminating its masks. But in light of the government guidelines on doing so, the company has been publishing technical bulletins, the latest of which finds that its N95 respirators can be cleaned without affecting the fit or function 10 to 20 times, depending on which FDA-authorized device is used.