UVC Sterilizer for COVID-19 Emergency

by bcrabtree

56K197182

Intro: UVC Sterilizer for COVID-19 Emergency

How to make a UVC sterilizer box. First things first. Electricity is dangerous! If you are not confident and competent do not attempt anything mentioned below. UVC (253.7nm) light is powerful, it can blind you and possibly give you skin cancer if exposed to your eyes or unprotected skin. Use a welding mask and protective equipment if you want to check the bulb function outside of the box (very strongly not recommended). If building one of these units please check with your hospital or local healthcare facility before just showing up with one.

The hospitals here, and nationwide, are running out of supplies. Our local hospital workers have to re-use their masks with NO way to effectively disinfect them. As this COVID-19 disease spreads we need to start working as a team to get this under control.

Over the past weeks I have developed a machine that can help our healthcare system cope with this. I have designed a UVC system that is able to disinfect reusable hospital equipment in minutes (n95’s, surgical masks, goggles, stethoscopes etc). This equipment is very inexpensive and easy to build. Currently our local ER's are using my systems to disinfect their PPE. These systems can effectively eliminate our n95 mask shortages. Any Engineer, Maker, STEM student, and capable handyman can make them. This will help take the stress off of hospital workers, as their disposable equipment can now be safely re-used.

How To make this:

STEP 1: UVC Sterilizer

Find a way to get your AC power into the box. Use either a cable gland, or a power socket.

STEP 2: Gather Up Your Components

For this you will need your circuit breaker, mechanical timer, limit switches, ballast, 2g11 socket and 2g11 UVC germicidal bulb.

(Look at pictures for actual layout and electrical schematic)

As soon as the power inters the box, connect the hot wire to the 2A circuit breaker.

Connect the neutral wire to the neutral on the ballast and connect the ground to the metal case of the ballast.

Connect the output from the circuit breaker to the input of the mechanical timer switch.

Connect the mechanical timer switch output to the normal open terminal (N.O.) of the first limit switch.

Connect a wire from the other side of the limit switch and connect it to the normally open (N.O.) terminal of the second limit switch.

Take the output from the second limit switch and connect it to the load (black wire) on the ballast.

From the ballast connect the blue wire to one side of the 2G11 base. If there are 2 blue wires, cap one of them with a wire nut. Cut the Red wire from the ballast output in half.

Connect one end of the red wire to the normally open (N.O.) terminal of the 3rd limit switch, connect the other end to the output from that switch. Attach the other red end to the 2G11 base across from the Blue wire.

Cap any other wires coming out of the ballast.

Now the fun begins.

STEP 3: Arrange the Box and Add Reflective Aluminum.

Now find a way to mount all of this inside the box!

Mount the bulb in the top of the box (see Photo).

Please note pictures are of a more complex computer controlled box with extra components (dc power source, din terminals, and a solid state relay), but you get the idea.

Please see comments from jfox240 below for additional pictures!

Group all of the electrical components on one side of the box to allow for maximum sterilization area. I suggest using acrylic to isolate the electrical components from the user.

Mount the limit switches so that they only close when the box lid is tight. I used a multimeter with the "tone" conductivity alarm. Attach your meter to the switches and position the switches on the inside of the box such that it has to be completely closed to engage the switch. Mount the switches tightly with screws so they do not move during heavy use.

Now coat the interior with reflective aluminum. I used 3/32 sheet and screwed it to the inside of the plastic. just make sure your electrical is isolated completely as aluminum will conduct electricity. A cheap alternative is to coat the inside of the box with aluminum tape. I also removed the pressure relief valve and filled the hole with hot glue to allow the user to see that the bulb is lighting up.

Now make some supports for masks, goggles, stethoscopes etc. I used clear acrylic and 50 lb fishing line to create a grid 1" above the floor of the box. This allows items to not touch the bottom, thus allowing reflected UV light to sterilize both sides. I also coated the acrylic with aluminum tape to increase reflection of UVC.

Check your UVC output from the bulbs actual UVC will vary. Thanks to Dr. Bohl for this information. It appears that UVC output is ~1/3 of the rated wattage from most bulbs.

So for a 36W bulb , we would have ~12W UVC (12,000,000μW) over an area of ~1440cm2 gives 8,300 μW/cm2. Over 1 minute this doses the items with ~ 500,000μW/cm2 or 0.5J/cm2. These values also decrease exponentially with distance. These are just calculations and your intensity will vary based on temp, bulb cycles, and reflectivity of UVC among other things. Ideally these can be measured with a UVC meter if available.

JUST OUT!!!! They made a room sized version!!!!

https://www.nebraskamed.com/sites/default/files/do...

Notes on variations:

I used instant start ballasts in this method as their strike voltage is high enough that I have never had a problem starting the UVC bulb. These ballasts do cause premature failure of the bulbs due to the sputtering of the filament material during the high frequency start. I intentionally chose this type of ballast as they worked with all bulbs that I could find. I had problems with several programmable start and rapid start ballasts as they had insufficient voltage to start the bulbs. Initially I thought this reliability tradeoff was worth the decrease in bulb life as bulbs were cheap and readily replaceable. We had our first bulb failure yesterday(unbranded bulb from amazon) it lasted ~1500 cycles and had significant discoloration near the filaments due to electrode sputtering. 1500 cycles is ok, but I think we can get better lifespan by using dedicated UVC ballasts of rapid start ballasts. I did get this rapid start model to work using two bulbs instead of one : https://www.homedepot.com/p/Philips-Advance-AmbiSt...

This type of ballast would be in improvement to the instant start as it pre-heats the filaments before starting. We should theoretically have an increased bulb life; we will find out soon. I will add a new diagram of this 2 bulb design tomorrow. Adding a bulb to the bottom of this unit will dramatically increase the UVC output, and allow better coverage of the underside of items without depending on reflection of UVC. If there are any ballast experts out there please message me so i can improve this design. I would like to get as long of a life as possible out of these bulbs as they are becoming harder to source and considerably more expensive.

******

If you want to make a micro-controlled version, simply wire the first 2 limit switches as inputs to the controller. send 1 signal high and 1 low then check the switches in the logic. Then use output to drive a SSR to control the ballast. I use a logic level MOSFET to drive the SSR with 12V, as this is less prone to have problems with EMI generated from the system. Also only use shielded wire for logic switches as the EMI will probably give faulty logic signals to the controller when this system is running. Always use a backup limit switch that directly controls the AC to the light if using a micro controller system as you need protection if the board malfunctions.

******

Great Articles on this method:

https://www.ara.com/sites/default/files/MitigateSh...

Associated smell after cleaning with UVC (smells like burnt hair) :

https://www.ara.com/sites/default/files/Amendment1...

Please see below comments for dozens of applicable journal articles on n95's.

*******

-Brian Crabtree

MS, BS Bio-Engineering from University of Idaho

To contact me please see my website. Please be patient as I am overwhelmed with questions currently. You can always contact the engineering and microbiology department at your local university if you have questions about this technology. I didn't invent this technology, I just designed a cheap, affordable and easy to make version.

www.crabsci.com

or

www.dripcoffeebrewing.com

Spokane WA

Have fun making this!

112 Comments

Suntechled 3 years ago

But does uvc light is harmful for human skin and eyeys?

LotsaHotsa 3 years ago

So sorry you have almost exclusively relied on amazon, when there are many other sources, otherwise I hope your idea makes your goal

bhambrewer 3 years ago

It would be great if you could share some of the alternative sources you mention to find some of these materials.

LotsaHotsa 3 years ago

Eric, I'm only a reader and I'm just saying that we should also be promoting small businesses who are dropping like flies during this pandemic. I would hope that you, as the writer, could do the sourcing, as you are far more familar than I who am only mildly curious, thanks

Captain_Nemo 3 years ago

The small businesses aren't "dropping like flies" because of the "pandemic", they're dying because of the politicians forcing them to close.

Captain_Nemo 3 years ago

Corona has a lipid shell, which can be destroyed by soap. Yep, you can remove corona with just soap and water (or laundry detergent). Isopropyl alcohol also works.

Article needs to be edited, as the following is no longer true, and is misleading:
"The hospitals here, and nationwide, are running out of supplies. Our local hospital workers have to re-use their masks with NO way to effectively disinfect them."

YoramG 3 years ago

As a biologist and the author of the UV-LED paper mentioned earlier (thanks shloime),
I would NOT trust N95 mask disinfected this way. The UV transmission of the mask material is neglectable the shape makes it very hard to properly disinfect. I suggest you take a look the IUVA wepage
https://iuva.org/iuva-covid-19-faq

Also, the comment made by UnitAE35ae, a UV device without UV meter is a risky issue, especially given that those lamps age and lose power.

Finaly, UV-LEDs are indeed mercury free.

KarenK160 4 years ago

Please research this before trying it. I've read UV damages polypropylene, care has to be taken not to damage masks, gowns, shields etc. Taken from a medical study site...."When sterilizing N95 masks, be wary of using UV light–keep N95 masks away from UV light / sunlight. N95 masks are degraded by UV light because it damages the electrostatic charges in the polypropylene material. It is unclear how long the masks can be exposed to UV light before they are ineffective."

paulzag 4 years ago

Like all your comments @KarenK160 you "read" but didn't cite a single source. "a medical study site" is not a source. While the article, other comments and many, many other sites do publish sources to the >10 years of peer-reviewed articles on this research. Even a link to an abstract would be helpful.

Yes we should not be re-using disposable N95 standard PPE. Guess what? Re-use better than zero PPE. And in this pandemic we are forced to re-use N95 disposable masks.

Research on the degradation is supported by peer-reviewed articles at 100+ to 1000+ exposure levels.

Being nice, I appreciate your taking the time to share a warning particularly with all the disinformation around. Please include a link to the article if you are capable of quoting it.

a-morpheus 3 years ago

I looked into building a germicidal UV sterilizer last spring (but in the end didn't build) and came across the same issue as mentioned by KarenK. Here are some links to papers/articles discussing the problem of filter degradation, strap degradation and tendency of straps to harbor germs since twists put surfaces in UV shadow, and also an article on other methods of sterilizing for reuse.
I think the takeaway for these hard UV wavelengths is to find the optimum exposure level--too short and you won't get enough sterilization, too long and after enough cycles (I don't know how many...research it) you might cause deterioration of some materials like plastics to the point where the mask probably isn't filtering at the level you hope it is.

1. "Ultraviolet germicidal irradiation of influenza-contaminated N95 filtering facepiece respirators"
https://www.ajicjournal.org/article/S0196-6553(18)...
Talks a little about UV dosage, W/cm2.

2. "Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC46994...
I'll include one interesting snippet from that about the various drawbacks of the methods:
"A variety of techniques for decontaminating N95 respirators have been tested, including autoclaving, steam generated by heat or microwaves, ethylene oxide, vaporized hydrogen peroxide, and bleach. All of these techniques have advantages and disadvantages. Heat and steam can melt or degrade the respirator and require drying the FFR after treatment.(10,12) Chemical disinfectants require rinsing and drying, and can leave an unpleasant odor or a residue that irritates the skin.(12) Gaseous systems using ethylene oxide or vaporized hydrogen peroxide require specialized equipment and ventilation controls.(11) N95 respirators cannot be disinfected with alcohols such as isopropanol because alcohols remove the electrostatic charge from the filtration media and substantially degrade its filtration capacity."

One interesting reference in that article: "Evaluation of Five Decontamination Methods for Filtering Facepiece Respirators"
https://www.researchgate.net/publication/26871567_...
-> https://academic.oup.com/annweh/article/53/8/815/1...

3. general guidelines on mask reuse
"Recommended Guidance for Extended Use and Limited Reuse of N95 Filtering Facepiece Respirators in Healthcare Settings"
https://www.cdc.gov/niosh/topics/hcwcontrols/recom...






shloime 3 years ago

simple (simplistic?) logic is that if the number of cycles is >1, it’s worth doing, because it reduces the amount of waste by at least half.

even capping the max number of reuses at 5 or 10 (just put an “x” on the item each time), greatly extends the effectiveness of the available supply.

yammv.

KOHNAN 3 years ago

So, I built 2 now, and they smell like they are working great. I brought one to the U.S. Navy shipyard that I work at to suggest they build and distribute, and came across an interesting dilemma...

Many of the areas in the shipyard and Mercury Exclusion areas because of the Nuclear reactor work that is going on there. Has anyone found mercury free UVC bulbs in their supply orders? Is that a thing? Is that a concern outside of a Nuclear shipyard, such as certain chemo facilities of a hospital?

After trial and error and some bad parts I was able to get the price to about $150 per unit, although starting over with what I found I could probably do it for about $115.

delwilson6241 3 years ago

An array of Far UVC LEDs will get you past the mercury issue AND provide a more even distribution of the UV light. Assuming this system is designed to alleviate the problems with the Covid-19 pandemic the optimum UVC light wavelength is 275-280 nm which is a little higher than the overall peak @ 260 nm.
Mercury vapor UVC lamps typically output in the ~254 nm range. That's close enough to be effective
A good source of aluminum sheet is https://www.mcmaster.com/standard-aluminum-sheets/.
Attaching components is easy if you use Velcro strips with adhesive; https://www.amazon.com/slp/velcro-strips-with-adhesive/yx6fxpaxpp338v7

Wjandrus 3 years ago

How did you get such a nice conformed metal on the interior of the case did you make a mold and press it?

Abkareeno 3 years ago

Use LED UVC by Klaran ,they are mercury free ,no need for ballast and high intensity

Wjandrus 3 years ago

What did your sanitize cycle length end up being?

Wjandrus 3 years ago

I feel like I am a little behind the curve on reacting to this pandemic in a quick thinking manner like you all have! Congratulations to all of you working to make these. I am starting my first prototype and would really appreciate any other tips you might share. I live in Canada and shipping from anywhere else right now is almost impossible. Main issue I am having is sourcing a suitable UVC bulb to start. Are there any Canadian thinkers making one of these. if so where are you sourcing your bulbs from. Lastly there is a waterproof fish tank UVC lamp you can get that has its own power supply, I am sure could be modified, but the max wattage is only 13 watts. Do you guys think 2 of these lamps would provide enough of a dose?

panchora99 3 years ago

How long must an item remin inside the box in order for it to be completly sterilized?
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