Imagine breathing through a face-hugging N95 mask for an entire eight-hour nursing shift on a hospital floor.

Properly fitted, it clings tightly to the skin, protecting the wearer from breathing in pathogens such as the coronavirus that causes COVID-19.

But those filtered-out germs don’t just vanish — the novel coronavirus can live up to 72 hours on surfaces, masks included. Just touching the outside of a contaminated respirator is risky, and it’s considered the biggest danger of reusing them.

Yet 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.

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.

That number grew by 523 cases Sunday, according to the Minnesota Department of Health’s daily tally. MDH also said eight more people have died of COVID-19 in Minnesota, bringing the number of deaths to 1,425 across the state.

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.

Paper bags, UV light

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.

Barb Galle, a registered nurse, said guidance on reusing masks well past their intended life is influenced more by supply problems than safe-practice considerations.

“Why would you think that it’s OK to wear a potentially contaminated mask, from room to room to room?” said Galle, a float nurse at the Minneapolis VA Health Care System, speaking in her role as president of the American Federation of Government Employees Professional Local 3669. “In a nurse’s heart and mind, that is so disgusting.”

A Minneapolis VA spokesman said the hospital has held its COVID-19 employee infection rate to 0.74% of its workforce, and it is providing all employees with required personal protective equipment (PPE).

Hospital officials say they have no choice but to reuse masks because the global supply remains constrained ahead of a potential second wave of COVID-19 cases in the U.S.

“We do safely reuse N95 respirator masks to conserve supply now and ensure we’ll have enough in the event of a COVID surge,” David Martinson, spokesman for Bloomington-based health system and insurer HealthPartners, said via e-mail. “While it’s difficult to predict how a second wave might impact PPE levels, the decontamination methods we use have helped us conserve N95s and keep our patients and colleagues safe, and we’re confident in our supply quantity.”

Health systems like Allina Health and North Memorial Health stressed that they’re following mask-use guidance published by the CDC and the U.S. Labor Department’s Occupational Safety and Health Administration (OSHA).

“We are confident in the level of PPE protection that’s provided to our staff and patients, whether that be a surgical/procedural mask or an N95 when treating COVID patients,” wrote Christine Hill, spokeswoman for Hennepin Healthcare in Minneapolis.

Covering the mask

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.

Mary Turner, a critical care nurse at North Memorial Health Hospital and president of the Minnesota Nurses Association, said she’s not happy about having to use one N95 mask over five work shifts. But it is better than having to use them for 10 shifts, as was the case at the start of the outbreak.

“I’m not going to be totally comfortable with the whole situation until we’re back to using the optimal standards that we learned in nursing school,” she said. “I can’t say that I’m truly OK with any kind of reuse. But that being said, it is what it is.”

Staff writer Kim Hyatt contributed to this report.