Can I use UV light to disinfect Totobobo filters?

Precaution!
– UV is very harmful to the eyes and can cause skin cancer.
– Conceal the UV light inside an enclosed space.
– Do not allow children or pet approach when the UV light is turned on.
– Some UV light generates ozone, which is harmful to the lungs.

Recently, we have received a couple of emails from our customers with the same question.

Can I use UV light to disinfect the Totobobo filters for reuse?
Does the UV light kill the filter’s effectiveness?

These are interesting questions that we have yet to explore. UV-C devices (tube or LED) for decontamination are not difficult to find nowadays. However, there is an obvious concern that UV exposure may degrade the plastic filter material and it may kill the static charges embedded in the filter media, reducing its’ filtration efficiency. After all, we all have seen how plastic turns brittle after long exposure under sunlight. What if the UV device turns the filter media brittle? or somehow reduces the static charges in the fabric?

We decided to do a simple test to find out how does the UV light affects the filtration efficiency of the filter media?
We use an off-the-shelf UV lightbox and conducted a simple exposure test on our filters (F94, F96, and Pro99).

The procedures of the tests as follows:

1: Perform a quantitative fit-test (TSI PortaCount Pro) and record down the result (fit factor=x) before exposing the filters under UV.
2: Expose the filters under the UV lights
3: Mount filters onto the mask
4: Conduct the quantitative fit-test again under the same condition.
5: compare the result before and after the UV exposure

How does the PortaCount machine works?
The PORTACOUNT measures the concentration of these particles around the person’s head and then measures the concentration of those particles that leak into the respirator.
The ratio of these two numbers is the “fit factor”. A fit factor of 100, for example, means that the air inside the respirator is 100 times cleaner than the air outside.

TSI PortaCount

Remember, the main concern we had was whether the UV exposure would in some way deteriorate the filter’s electrostatic charge and degrades the efficiency and mechanical property. Read more below to find out!

We started the test off with a 1-hour UV exposure, to our surprise, the fit factor remained at the top level (200+), same as before the UV exposure.
The fit-factor is determined by two parameters, (1) how well the mask fits the face, and (2) the filtration efficiency of the filter media. Since the first parameter is fixed (same person, same mask), a change of the fit-factor would indicate a change of the filtration efficiency.

We decided to push it further, to a longer time frame of 3 hours. The results remained the same, showing the filters are holding the performance at the top-level even after 3 full hours of exposure to strong UV light.

Encouraged by the results we’ve gotten for the previous 2 tests, we decided to go another step further. We let the UV rays shine upon the 3 different sets of filters for an additional 2 hours, accumulated a total of 5 hours of UV exposure, and then perform the test again. The results remain the same! These filters are as good as new after a 5-hour under very strong UV radiation.

Frankly, we were quite surprised and impressed by the performances. Initially, we thought the UV radiation would destroy the filters and degrade its filtration performance. It turns out that the filtration efficiency is not really affected by UV light exposure.

In conclusion, filter efficiency is not likely to be affected by a few hours of UV exposure. (e.g. germicidal UV-C light) Such duration is more than enough to provide 4-5 times of 15 minutes UV-C decontamination sessions.

For additional safety, we recommend changing the filters after each visit to a high-risk area (i.e. crowded hospital). Disinfect the used filter with UV-C and rest for a minimum of 3 days in a clean space before reuse.

Precaution!
– UV is very harmful to the eyes and can cause skin cancer.
– Conceal the UV light inside an enclosed space.
– Do not allow children or pet approach when the UV light is turned on.
– Some UV light generates ozone, which is harmful to the lungs.

Reference reading:
Addressing COVID-19 Face Mask Shortages [v1.1]
Evaluation of Five Decontamination Methods for FFPs
FB: Open source COVID19 medical supply

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