UV Light Disinfects Masks, Harms Filtration Less Than 2%

While masks are in short supply during the coronavirus pandemic, the shortage is prompting people to ask UV light disinfects masks. This is a critical question for frontline healthcare workers, as they scramble for ways to safely re-use masks

Re-use masks infection

 

Here’s the problem. We know that UV light kills bacteria and viruses, but we also know that UV light degrades fibers. That means it’s crucial for healthcare workers to know whether UV light reduces the effectiveness of masks. 

 

 

Putting It to The Test: Does UV Light Harm Mask Performance?

 

Researchers got hard data on this question by testing four N95 masks before and after UV sterilization.

 

Can UV Light Disinfect Masks

 

They tested four models of N95 masks: the 3M 1860, 3M 9210, Gerson 1730, and Kimberly-Clark 46727.

 

 

They exposed masks to five different doses of UV light (also called “UVGI”) from 120 to 950 J/cm².

 

UV Light Disinfects Masks, But at What Dose?

 

These are high doses. Even the lowest dose is 66 times higher than a dose that researchers found is sufficient to deactivate 99.99% of viruses on masks (1.8 J/cm²).

 

UV Light Sterilization Hospitalk

 

To test how well the masks could capture particles, they shot tiny pieces of salt from 0.02 to 0.4 microns at the masks and measured what percentage penetrated the masks. This range of particle size covers the size of flu, ebola, and coronavirus particle sizes.

 

Size of coronavirus particle pm2.5 and bacteria

 

They tested 10 different sizes of particles and used the data for whichever size particle penetrated the mask the most.

 

UVGI Disinfection Dosage

 

UV Light Harms Mask Effectiveness Less Than 2%

 

The data showed almost no harm to performance. For most masks and most dosages, the degradation in particle capture was less than 1%.

 

UV Light Disinfect Masks Harm Performance

 

In only three tests was the harm above 1%. And even in the worst case, the UV light caused degradation of under 2%.

 

UV Light Sterilization Harms Straps More Than Filtration

 

However, capturing particles isn’t the only things mask have to do. They also have to keep their shape and fit to the face. Thus, the researchers also tested how the UV affected the structural integrity of the masks.

 

N95 mask UV light structural integrity

 

One test they did was to pull the straps as hard as they could until they broke. The tests found that, at higher and higher doses of UV light, less and less force was needed to break the mask straps.

 

UV Light Disinfection Harms Mask Structural Integrity

 

Besides the effect of UV light, the data also showed that masks with rubber band straps (3M 9210) broke far more easily than masks with elastic straps (3M 1860). This strength is also important for people who need to re-use masks. Masks with fabric straps will last longer on average than masks with rubber band straps.

Elastic versus rubber band N95 mask straps

 

A Simple Way to Tell If Mask Needs to Be Disposed

 

If healthcare workers are going to use UV light to disinfect masks from COVID-19, they’re going to have to solve another question: how many times can I disinfect the mask? One dose–even a strong dose–had only a small effect on performance, but surely repeated doses will have a cumulative effect.

The researchers suggested the answer lies in integrity. They found that, besides the straps, the UV light “dramatically affected” the structural body of the masks. The researchers suggested that (at least for some masks) masks will fall apart before they lose their ability to filter particles.

 

 

This is important because healthcare workers don’t have laser particle counters to continually test how well their masks are performing. So how do they know when it’s time to throw them out?

The scientists suggested people can use the structural degradation as a signal. Put simply, when the mask starts to fall apart, that’s a sign that they should throw the mask away while knowing that filtration performance has likely not dropped severely.

 

UV Light Disinfects Masks: Bottom Line

 

UV light disinfects N95 masks with less than a 2% harm to filtration effectiveness, allowing them to be re-used quickly.

 


Better Options Than Disinfecting Masks With UV Light

This finding is similar to results of washing masks with soap and water, which also harms performance. Instead, research shows that  simply drying and waiting as better options for disinfecting masks.

 

Read more: This proven disinfection method deactivates viruses with zero harm to mask performance.

 

Disinfect N95 mask wash alcohol viruses


Covid19 coronavirus best masks materials fundraiser

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jim

Thank you for this clear and sensible information. Hard to find info that doesn’t leave gaps or questions open. A job well done! You deserve a raise!

Rosanne

How about disinfecting a mask by leaving it outer surface up on the car dashboard, being irradiated by sunlight and also exposed to the heat from sunshine building up inside the car? How many hours might this take to render the virus non-viable? I am doing this currently with the surgical masks I use whenever I go out – when I leave the car to go into my house, I leave the mask sunning itself on the dashboard.

Liz - Smart Air

Hi Rosanne, Liz here from Smart Air. Good question! I looked it up and most cars windshield glassed have been treated with UV protections. So they can block out most UV light, although we always feel the heat accumulated on the front deck under the windshield. I would recommend to leave the mask on your porch or balcony where there is enough sunlight and good airflow instead.

rajesh

Thanks for publishing

Nik

Can you show us what is the best way to make a mask at home? I know there is a lot of Youtube videos, but none of them have tested them.