I know that today’s surgical masks were designed for single use, but given the shortage, can these masks be sterilized and reused? The coronavirus on inanimate objects can be killed with Lysol, so could masks be sprayed? And what about autoclave sterilization? Would a surgical mask (or gloves, shoe covers, etc) survive the heat?
Stanford just released a study showing masks (caution - PDF) that heated to 70C for 30 minutes safely disinfected the mask without impacting filtration ability.
Autoclaves use pressurized steam at 120C to sterilize medical equipment. It’s surprising that dry heat at 70C would be adequate.
Probably viruses are more fragile than bacteria. That’s about 160 F by the way. The lowest setting on my stove is 170; I wonder whether the masks would survive that temperature.
Based on some research I did for homebrewing and sous-vide cooking, disinfection/sanitization is very dependent on both temperature AND time.
Autoclaves are a combination of high temperature, pressure and steam to relatively quickly and effectively sterilize things, including spores and very tough bacteria and viruses. But you can duplicate the same effect with dry air for different periods of time and temperatures.
Look at it this way (by analogy)- the USDA safe temperature guidelines for food are the temps at which the food only has to be heated for around 1 second to effectively pasteurize the food, which for chicken is like 165 F. But you can accomplish the same reduction in bacteria by heating it to only 145 for a much longer time- on the order of minutes, not seconds. But in the end, the effect is the same.
I imagine autoclaves sterilize in a matter of a handful of minutes, while baking a mask takes half an hour at minimum.
They also mentioned UV light was just about as effective as heating the mask. Would leaving the mask in the sun work to provide UV sterilization?
I think the problem is how do you measure it? If I want to ensure it’s sterilized I can use a known heat x time. How much UV is falling on the mask? Is the elastic band casting a shadow? Did a cloud go by?
Yeah, those are all valid concerns and what I’m wondering about. If you have several masks, perhaps they could be hung outside and you rotate through them so it’s in the sun for a full day. UV sterilization from the sun might be a valid option for items which can’t go in the oven, like computer accessories, phones, shoes, etc.
One thing to keep in mind is if you put something in the oven to sterilize it, it should probably be inside something to protect it from direct infrared heat. Even if the oven air is 70C, the IR heat may make the surface of items in the oven much hotter. It’s like how the outside of toast burns because the IR heat from the burner is greatly heating the outside of the bread. The air in the toaster won’t brown the toast. It’s the intensity of the burners. The same thing would happen with a mask. The intense IR from the burners would “toast” the outside of the mask when they were on.
For something like sterilizing a mask, I would think you would need to protect it somehow. For example, put the mask raised up in a ceramic pot with lid and with a probe thermometer to measure the air in the pot. That way the ceramic pot would absorb the intense IR heat when the burners are on and the mask would not get hotter than the 70C air inside the pot.
I just heated up a few N95 masks to 200 F for 30 minutes. There was no visible damage to the masks. This is not something I would normally recommend, but times being what they are we have to do the best with what we have.
Wait, people miss the key point of the study, read the quote.
It’s not a study on killing the virus, it’s a study on killing the virus without destroying the mask. In the study, shows an oven, or steam, might destroy the virus, without destroying the mask. An autoclave or other extreme measure of course destroy virus, but it destroys the mask filtration also.
That’s whats interesting.
Fudan University in China (ranked one of the top 50 universities in the world) published a study on Feb 9th saying basically the same thing as the Stanford study and this has been well known in China for months now.
The key difference between viruses and bacteria is that viruses can only reproduce inside a living host so the viral load on any object can only go down over time. The standard practice that was considered safe in China was to have enough masks so that you didn’t need to reuse one for at least 5 days. Other sterilization mechanisms were used in conjunction with this when appropriate but all other forms of sterilization degrade the lifetime of the mask so just letting it sit was considered the most prudent mechanism.