Disposable respirators are supposed to be single use items - up to a few hours to a day.
The CDC noted in the above image to make sure to discard respirators/masks once used.
However, many people are trying to find ways to decontaminate their masks in order to re-use them. 3M, the world's largest manufacturer of disposable respirators, said that "no disinfection method..has met their key criteria"(3M).
That being said, there is also research that shows that respirators and masks don't degrade quickly when put to use. The team at SmartAirFilers found that their masks only lost 1.4% of their filtration capacity after being used in Beijing over 11 days.
This is remarkable and indicates that reuse of respirators and face masks, while not recommended, might be okay a short period, if no other alternatives exist. Corona 95 Masks.co reiterates that our recommendation is to make sure you have a supply of respirators / masks (N95s, KN95s, FFP2, etc) that you can use and dispose of without concern.
|Suitable Decontamination Options||Poor Decontamination Options|
|Time & Heat||Washing|
Time & Heat
One of the simplest methods of decontamination (with the coronavirus SARS-CoV-2 in mind) is to store a used respirator for enough time that the virus is no longer active. A recent study published in NJEM (link) found that the length of time the virus remained active depended upon the surface it was on.
With the longest duration being 72 hours (3 days) on steel and plastic.
A recent study appeared (link) from Hong Kong researchers, that found a “significant level of infectious virus could still be detected on the outer layer of a surgical mask on Day 7”. As surgical masks perhaps sharing similar material to respirators, this is worth taking note of.
Temperature plays a role too. A study (link) using SARS-CoV surrogates found that viruses died faster as the temperature increased, with 40C killing them faster than 20C.
Overall this suggests that time and heat will decontaminate respirators. However, whether 72 hours or longer is needed still remains unclear and warrants further research. For settings in which a fast turnaround for respirators is needed, this strategy is likely to be inadequate.
Experiments performed by 4C Air and mentioned in Stanford research found that 70C (158F) oven heat for 30 minutes was capable of killing E.coli bacteria, which they used as a substitute for the coronavirus (SARS-C0V-2), due to the lack of availability to study live novel coronavirus directly.
Critically, they found that after this heat treatment, the respirator had lost less than 1% of its “meltblown fiber filtration media” and 8% of its “static-charged cotton” filtration efficacy – seen below in the table:
One thing to note is that the results in killing E.coli were used as a simulation for SARS-CoV-2 (COVID-19, Coronavirus), but these results haven't been confirmed yet.
The same study as above, also found that hot water vapor from boiling water for 10 mins was also capable of killing E.coli bacteria without causing a big reduction in filtration capacity of the respirator.
Ultraviolet light is part of the spectrum radiated by the sun. We’re particularly familiar with UV-A and UV-B, which cause skin damage, and sunscreen aims to block. UV-C is also emitted by the sun, but due to it’s shorter wavelength, it gets blocked by the Earth’s atmosphere and ozone layer.
UV-C doesn’t reach the Earth, and as such, organisms haven’t evolved defenses against it. As a result, a short amount of exposure to UV-C will kill simple organisms.
A hospital in Omaha, called Nebraska Medical, has publicly documented (link) their use of UV-C to decontaminate their hospital’s N95 (KN95, FFP2) masks / respirators.
- They estimate RNA viruses like SARS-CoV-2 (COVID-19, Coronavirus) should be inactivated by 2-5 mJ/cm2 of UV-C
- For caution, they use upto 12x that dose, so 60mJ/cm2. For every round of sanitization
- They use a product called “The Torch” by ClorDiSys which uses 8x 254 nm bulbs, which produce 200 μw/cm2 at 10 feet distance for a dosage of 12 mJ/minute.
- They monitor dose using a UV meter. They can monitor, start and stop the process from outside the room. This is great, because UV-C can damage human cells too (eyes and skin are the first hit), and needs to be avoided. It can’t pass through walls however, so being outside the room is adequate.
- They covered the walls and ceiling with a UV-reflective coating from Lumacept. This allows sections of the respirator not in direct line of sight from the UV-C bulb to still receive light radiation. Regular paint on walls and ceilings would hinder this by absorbing the light, rather than reflecting it.
- They intend to extend use of their N95 (KN95, FFP2) respirators until respirator fit is impacted (they discuss this a bit more here).
More details here in their PDF guide
In the same way that we can wash our hands with soap and remove the SARS-CoV-2 (COVID-19, Coronavirus) particles, we can potentially do the same with a respirator or mask (N95, KN95, FFP2). However there is some research to show that washing a respirator will dramatically decrease its filtration capacity.
SmartAirFilters found that washing their respirator reduced its filtration capacity by 21%, which is a huge drop:
Part of the reason for this is that N95, KN95 and FFP2 respirators use “electrostatic attraction”, and washing damages this. For the electrostatic attraction layer to work, oppositely charged particles are attracted to a charged fiber, which aids in the collection of both larger and smaller particle sizes (see CDC link for more info). We can also anticipate that washing (especially vigorous) might damage the fibers.
Whilst we have sources to suggest that 70%+ alcohol is effective against SARS-CoV-2 (COVID-19, Coronavirus) (see CDC link), the risk is that it damages the filter capability. In particular removing the electrostatic charge applied to N95, KN95, FFP2 respirators.
Experiments performed by 4C Air and mentioned in Stanford research, suggest that soaking and then drying in 75% alcohol reduced filtration capacity from 96% to 56% – which is a dramatic loss of function.
Right now there is no proper solution to reuse respirators or masks such as the N95, KN95, or FFP2 models after extensive use. Most methods of decontamination have significant trade offs that can damage the integrity of the filtration system.
Therefore it is recommended to NOT reuse respirators, if possible
Thank you to John for the original post.