In an effort to prolong the life of N-95 face masks, many institutions have been using UV-C light disinfection. It is being looked at by
3M and they list testing results on their masks. FDA recommends following the guidelines of the manufacturer for UVC decontamination procedures. CDC references a article from the
Infectious Disease Journal providing guidance on UVC decontamination. The CDC lists UVC as a
method of N-95 respirator decontamination.
Here are some safety notes to note up front. UV-C light is hazardous. Do not expose skin or look at the light as it will cause damage. The light must be turned on remotely without individuals present in the room. The lamps can get hot, and ozone may be produced.
There are concerns with making sure all parts of the mask are disinfected. There are also concerns that the UV-C light will cause the material to photo degrade and loose its effectiveness.
Not all UV lights are equivalent (notes from Nancy Rolstad and
Wikipedia UV)
- UV-A lights (the ones used in a tanning bed) do not have sufficient germicidal properties (long-wave UV) It is associated with skin aging
- UV-B light is a shorter wavelength of light associated with skin burning.
- UV-C lights are necessary for disinfection. (aka UVGI germicidal irradiation or shortwave UV)
- UV-C light bulbs efficiency is reduced over time. A UV meter is necessary to measure the quality of the light source.
- UV-C light is absorbed by the ozone layer and the atmosphere. That is why the sunlight that reaches the earth does not have good disinfecting properties for COVID-19.
J. of
The
University of Nebraska has excellent guidance on the use of UV-C light for COVID-19 disinfection including information on a
COVID-19 UV-C decontamination process They also looked at using the
UV-C lights in biological safety cabinets to disinfect masks. The University of Nebraska produced specific information on
UV-C light respirator decontamination. The
AMA has a brief description of the process.
Stanford University also has a
UV-C COVID-19 disinfection process.
In
Science Daily: Researchers report a 99.9% reduction in surface COVID-19 levels with a 30 second dose of UV-C light. The dose was not specified.
U of M's
CIDRAP has weighed in on N-95 reuse. Current methods are for an emergency use only to extend the amount of stock available. The UV-C light does begin degrading the material. Under the emergency circumstances they recommend 5 cycles at 1 J/cm2 per cycle.