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N95 Respirator Masks: Clean and Reuse?

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It seems that each week during the COVID-19 pandemic, there is one primary topic of discussion in the Shapiro household. Last week it was an emphasis on the exponential growth curve of the virus – still happening in California, among many other states. At the point of my writing this editorial, the United States is known to have the largest number of COVID-19 cases in the world, and it was reported that we could see up to 100,000 – 200,000 deaths.¹ This week, as I’m back to work seeing patients (our clinical faculty is on a rotating schedule of one week on and 1-3 weeks off call and clinic in case one of us is exposed and needs to quarantine) the conversation is about N95 masks. Like all caregivers, I have a limited number of N95 respirators, so I’ve spent time trying to figure out how many times I can use a mask and if it is possible to decontaminate a mask. Unfortunately, there isn’t a good evidence-based answer to this yet. Each method seems to have its limitations. Let’s find out more about this respirator mask to understand the protective equipment everyone is talking about.

First, in case you’ve been listening to medical podcasts there’s one small piece of information worth noting about the name of this pandemic. The disease caused by the virus is called COVID-19 while the virus itself is termed SARS-CoV-2 (severe acute respiratory virus syndrome coronavirus 2).

What’s so Special About the N95 Mask?

This respirator is very different from a surgical mask, which is loose fitting and made to keep particles from the wearer (the surgeon and staff) from landing on the patient. Because the surgical mask is open on the sides it does not provide protection for the SARS-CoV-2 virus. This is the reason why it makes no sense for those not ill to wear a surgical mask – it doesn’t protect us. It is, on the other hand, useful for those who are ill, so the productions of their cough stay within the mask. Here are some bullets about the N95 respirator:

• Production is regulated by the National Institute for Occupational Safety and Health (NIOSH).
• N = “Non-oil” respirator rating, ie, it does not filter out oils in the air. For that you would need R (oil proof for 8 hours) and P (completely oil proof).
• 95 = 95% efficiency. Masks ending in “100” have a 99.97% efficiency, which is the same as a HEPA filter.
• These masks filter out particles 0.3 microns or larger as well as large droplets. Not to freak anyone out, but coronaviruses are 120 nm (0.12 microns) in size, about half the size of the smallest particles the N95 filters.
• Material: This is an electrostatic nonwoven polypropylene fiber made from millions of microfibers stacked on each other. It is placed between two other fabrics to prevent abrasion of the filter. The filter fiber is charged in an electrical field to ionize the filter making it 10 times more effective than it would be if it weren’t ionized.²

Can You Clean and Reuse the N95 Respirator?

This construction is why it has been so difficult for the medical community to clean and reuse the masks. For example, chlorine-based products seem to do a good job cleaning (though no one has studied this coronavirus’ response yet). However, chlorine eliminates the electrostatic charge in the respirator, an important aspect. Besides, it’s not terribly safe to breath chlorine! So…don't use chlorine.

Schwartz and colleagues at Duke University found using 35% hydrogen peroxide vapor to decontaminate N95 respirators was successful in allowing safe reuse.³ Price and Chu from Stanford reviewed this unfortunately sparse topic and made this suggestion: “70C /158F heating in an oven (not your home oven) for 30 min, or hot water vapor from boiling water for 10 min, are additional effective decontamination methods.”⁴

Amanda Deskins, DO gets the award for single most logical idea when she contacted retired Dr Peter Tsai, the person who invented the fabric in the N95 mask.⁵ He explained that because the masks are hydrophobic, the virus won’t be able to live on it. He reminded us that the virus lives on metal surfaces for up to 48 hours, on plastic for 72 hours, and on cardboard for 24 hours. As a result, he recommended the following protocol:

Take four N95 masks and number them 1-4.

On day 1, use mask #1, then let it dry out for 3-4 days.

On day 2, use mask #2, then let it dry out for 3-4 days.

Same for day 3 (mask #3) and day 4 (mask #4)

Based on everything we know about this respirator, it’s no wonder we’re supposed to throw them away after each use and why we need so many of them. For me, understanding how the mask works, as well as its limitations, provides some measure of comfort. I’m staking my own health on Dr Tsai’s recommendation and using the protocol he described. Hopefully these suggestions will keep us healthy enough to continue our caregiving responsibilities. Stay healthy!