Welcome to the Osmosis daily report on the coronavirus pandemic. I'm Dr. Rishi Desai and I'm the chief medical officer at Osmosis.
I'm also a pediatric infectious disease doctor and I used to work at the CDC in the division of viral diseases. Today
we're going to talk about recycling N95 masks. So as we know, there's a shortage of N95 masks for healthcare workers.
And there's a page on the CDC website that addresses this directly. It's called Strategies for optimizing the supply of N95 respirators.
If we scroll down there's a section
here around extended use of N95s.
And they actually specifically call out how long you should be using them for. They say when practicing extended use the maximum recommended time
is up to 8 to 12 hours.
So let's say 12 hours is the maximum time. They go on to say respirator should not be worn for multiple work shifts
and should not be reused after extended use. So essentially what they're saying is
one mask can at most be used for 12 hours and then you should get rid of it.
Now that's a big challenge for a lot of places that don't have N95 masks. And in fact, in practice
a lot of clinicians are taking N95s home with them and reusing them day after day.
So Stanford medicine has worked on putting together this document
from the anesthesia informatics and media lab and partnership with learnly.
So these folks have said, "hey, can face masks be safely disinfected and reused?" So it's a great question. It's very relevant.
And they go on to say very clearly there are some methods of N95 mask disinfection
that can work over multiple disinfection cycles. But a couple of things.
A,
this is not NIOSH approved,
and B,
the the exact changes to the mask itself are not well understood.
And so this is where they did a research study to kind of show and understand
how
putting a single mask through multiple cycles would affect that mask.
So they looked at three key ways of doing this. The first was hot air. They said, okay
let's go ahead and preheat the oven to 75 degrees celsius.
Let's put some samples in the oven and then let's let them essentially cook or bake for 30 minutes. After that
let's let them cool for 10 minutes. And then they actually did this to the same mask
20 times. So over and over and over they would do this and they wanted to see
whether the mask would break down and whether it would still work after 20 cycles of this.
So you can see they started with an initial filtration efficiency of about 97.44%.
And then when they did this to these masks 20 times at the end of it the filtration efficiency was 95.96%.
Right here... so really not that different.
And so that's actually pretty reassuring that even though you're cleaning these these masks 20 times over
they're still working the way that you would expect them to work.
So then they used a second disinfection method and this was using UV light. They irradiated with UV light using these specifications
for 30 minutes and then they did it again. They let it kind of
be out for 10 minutes and then they put it through another cycle.
They did this again over and over and over again 10 cycles to see again what the filtration efficiency would be
at the end of that. And here they ended with 96.78%
efficiency so again really high efficiency even after 10 rounds of UV light. The third approach they tried was steam.
They would steam these for 10 minutes, the masks, and then they would let them dry
and then put them through another round. They did this again 10 times and then checked the efficiency at the end of that.
This time the efficiency fell pretty dramatically. So you can see after 5 rounds it was 86
and then after 10 rounds it was
77.77% efficient. So here, unlike the first two examples, there was a big decrease that you were seeing
in the efficiency of the filtration after just 5 or 10 cycles of it. So some key conclusions they drew from this
is that method one and method two seemed pretty effective, meaning the heat
and using the UV light. They did say that the UV light may
be not penetrating all the way through the mask. They said that may limit the disinfection capabilities
for maybe some virus that's deep within the fabric. And then for the heat method they pointed out that actually even after 20 cycles
the mask didn't have any deformation. It wasn't shaped any differently, the elasticity of the bands didn't degrade,
they were still usable, so clearly from this it seems like
the hot air approach is the best one.
They did it for 20 cycles, had good filtration efficiency.
The mask was looking and feeling right at the end of it, with good elasticity of the bands.
So that seems like one of the
best outcomes here. Now, they do make a big point and right up front they can see this kind of image here
they say do not use anything in your home to disinfect
contaminated equipment. Specifically they say do not use your home oven. That's not what they used in the study.
What they would recommend is someone in the hospital setting actually doing this for a large cohort ideally of masks and
cleaning those masks so that people can use them again and again.
Okay, so with that, thanks for tuning in. Please make sure you subscribe and hit the bell icon to get daily notifications. Go to
osmosis.org/covid-19 for all of our resources.
Remember to flatten the curve and raise the line. We're all in this together. Thanks a lot.