Responding to concerns over the repeat use of disposable respirators, Maplewood manufacturer 3M Co. said it may be acceptable to use vaporized hydrogen peroxide systems to decontaminate used N95 masks during a crisis like the COVID-19 outbreak.

Some Twin Cities hospitals are using ultraviolet light to decontaminate used respirators, which 3M testing has initially found to be acceptable, though the U.S. Food and Drug Administration has not yet granted any company authorization to market UV-sterilization services for respirators.

3M said Thursday that the only method that has obtained FDA emergency authorization and met 3M's own requirements during testing to deactivate the virus while not damaging the mask is the use of vaporized hydrogen peroxide in systems offered by Steris, Advanced Sterilization Products and Batelle.

When fitted tightly to the face, an N95 respirator is intended to filter out 95% of small particles down to 0.3 microns in size. That's why N95 masks are commonly worn in health care settings to filter out airborne particles, including disease-causing pathogens.

The global supply of respirators during the COVID-19 outbreak has become a key bottleneck in the health care system, along with mechanical ventilators and hospital intensive-care beds. Vice President Mike Pence visited 3M's Maplewood headquarters early in the federal response to COVID-19, and President Donald Trump later declared that 3M was subject to the Defense Production Act.

3M is increasing production to a rate of 2 billion respirators annually, and importing another 167 million to the U.S. in the next three months.

Yet the supply of personal protective equipment remains so tenuous that the U.S. Centers for Disease Control and Prevention earlier this month said that health care providers may need to find ways to reuse and decontaminate disposable N95 masks. The CDC put out a detailed guide for when and how to do so.

However, decontaminating and reusing N95 respirators is not an approved practice under normal circumstances, and little published evidence exists on the best ways to do it.

3M has been testing ways of decontaminating its respirators for years. The company said Thursday that a key weakness of many of the published studies by other companies is a failure to consider all four factors that 3M sees as essential: The virus must be deactivated; the decontamination can't damage the filter; it can't change how it fits to the face; and the mask has to be safe to wear afterward.

"If, as a result of decontaminating a respirator, the filtration is damaged or the respirator does not fit, it will not help reduce exposure to airborne particles at the level indicated, such as N95," 3M's statement Thursday said.

With those factors in mind, 3M sent batches of respirators to outside companies that were proposing to apply to the FDA for emergency use authorizations (EUA), and then evaluated the state of the respirators that came back.

3M said UV-light systems made by Xenex successfully passed 3M's requirements for acceptable decontamination, but the FDA has not yet granted an EUA.

3M says the use of ionizing radiation degrades the filter performance, and is not recommended. Also not recommended is the use of microwave radiation, which can compromise the device's fit by melting the respirator near metal components. For the time being, 3M also does not recommend the use of high temperatures, autoclaves, or steam because of significant filter degradation.

Finally, 3M does not recommend using the controversial sterilization agent ethylene oxide because the chemical is widely believed to be carcinogenic when inhaled at high quantities.