UV Face Mask Sanitizing Box
Mobile mask sterilization stations that can be used to clean up to 32 masks at a time. The system uses ultraviolet C (UVC) light, a short-wavelength light capable of converting the virus into harmless carbon compounds and water.
Traditional UVC bulbs are also short supply because of the pandemic. Prototype system uses a more readily available LED bulb also capable of reaching the needed frequency for germicide.
- Will sanitize mask in less than 10 minutes.
- Grill rack in the middle to radiate from top and bottom.
- Safety switch to turn off UV lamps for accidental lid opening.
- Timer switch to control radiation timing from 2- 15 minutes
- Pilot lamp to indicate if UV is ON.
- Inside surface is made reflective using aluminum tape or glued aluminum foil.
- The lid has 3/4” lip around to prevent UV light from escaping when closed.
- Locking system to keep away from unauthorized use.
- The usable surface area of the unit is 11 square feet (5.5 ft x 2ft). It can hold up to 32 masks (6” x 8” masks) in four rows.
- Information Sheet (PDF)
- Box Dimensions = scalable as needed
- Mask Capacity = scalable as needed
Frequently Asked Questions
The studies shows that only UV-C range of ultraviolet light is effective in killing the virus. UV-C has wavelength less that 280 nm but most UVC lamp has 254nm wavelength. UV-A and UV-B are not proven effective for this application.
The target UV dose for wavelengths around 250 nm is 1J/cm^2 to deactivate virus similar to SARS-CoV-2 on N95 as recommended by a the University of Nebraska report (https://www.n95decon.org/uvc). With the UVC bulbs we are using, a treatment period on the order of 15 minutes will achieve this level.
We have few dozen at hand. But Joe Kaufman, one of our Alumni and who has provided these bulbs to us, says he can get more if needed. Also, there are vendors who carry those bulbs.
The unit should kill virus provided there are no obscured surfaces. If UV light can't reach a spot, there is a possibility that the virus will survive at those places. I do not believe there is any easy way to test if all virus has been killed. We are designing this from a study that 1J/cm^2 or higher amount of UVC radiation is enough to kill SARS CoV2 virus. Also, it is possible that objects life will degrade from exposure to intense UV light. So we would suggest to evaluate your situation looking at objects you want to sanitize and make the best judgement.
Here is the procedure, in a nutshell and then detailed.
- Find the killing dose (for SARS CoV-2, it is > 1 Joule/cm2)
- Find the Watts of UVC radiated (Bulb spec sheet)
- Find the power density at the weakest location in the sterilizer. See discussion below.
- Divide killing dose by power density to get kill time.
It takes a killing dosage of one Joule per square centimeter of UVC radiation to kill the corona virus, according to several medical and bioengineering papers that I read. In researching a host of UVC tubes, I found that their efficiency in converting input electrical power to radiated UVC is almost always about 35% to 40%. Therefore, to get the wattage radiated as UVC, divide the rated input electrical Watts by three. Now calculate the surface area of a cylinder whose radius r is the distance from the fluorescent tube center line to farthest point that you want sterilized; h is the length of the fluorescent tube. Area = 2 * pi * r * h. To get the power density, divide Watts UVC by the Area. Now divide the killing dosage by the power density. Joules per sq cm divided by Watts per sq cm is seconds. The result is the killing time. Do your calculations with units as we taught you to do in basic college Chemistry and Physics as a check on your work.
If you want greater accuracy and a quicker kill time and you have more than one tube, power densities sum as vectors. If vectors are not your thing, add together all the power densities that you calculate from each bulb to the farthest point that you want sterilized and multiply by 0.7 to get the total power density. The math behind the 0.7 is trigonometric, a cosine function or a dot product, and assumes an angle of no more than 45 degrees formed by the two bulbs and the farthest point, a pretty reasonable assumption. But this summing of power densities is probably too complicated. Skip it if you prefer and just calculate the kill time from the nearest tube and leave it at that.
Some have suggested sterilizing twice to be sure that the virus is dead. As satisfying as that may be, it is a bad idea. Dead is dead; trying to kill something already dead is wasteful. UV light is well known to degrade the quality of many materials such as plastics and rubber. Hitting the equipment a second time means one fewer sterilizing cycle available before the gear wears out. Most of the papers that I read seem to indicate that at least ten sterilizing cycles can be done without risking PPE equipment performance.
We recommend buying UL listed sterilizing equipment whenever possible.
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