Sunday, March 22, 2020

Recycling N-95 masks

One of the local oncology wards is running out of N-95 masks. They are cutting masks out of cloth (to a pattern supplied by the CDC!) for the folks not in direct contact with patients.

I asked my contact if they had ever considered sterilizing the nominally disposable masks by placing them in a refrigerator with an ozone generator running.

Virus is relatively fragile. Ozone is a gas and permeates.

I believe it comes down to a time-concentration-temperature calc.

I volunteered the ERJ ozone generator if they want to give it a try.


  1. I would think you could autoclave these masks for reuse. Worst outcome would be the need for new elastics.

  2. I have read that the Covid19 virus can survive on certain surfaces for up to nine days. That seems unlikely to me, but let's assume it's true. I have also read that the survival time in full sunlight is measured in hours rather than days. And in full sunlight in a hot climate it is probably minutes rather than hours.

    So just hang them outside somewhere in full sunlight for a full day and you would probably be okay. If you want to be extra cautious, make it two days, with the outside of the mask facing the sun one day, and the inside facing the sun on day two.

  3. Microwave oven?
    Recommended Guidance for Extended Use and Limited Reuse of N95 Filtering Facepiece Respirators in Healthcare Settings:

  4. I believe I've mentioned this in comments before, but here is an article from the January 4 2017 Nature about impregnating filters with a salt to kill viruses. The salt doesn't chemically kill the virus, instead as the salt that gets dissolved in a droplet crystallizes as the droplet dries, the crystal edges chop up the virus.


Readers who are willing to comment make this a better blog. Civil dialog is a valuable thing.