Introduction: UV Disinfectant Cart
The global pandemic has freaked out my family and staff at my store. Bringing things into our personal space has a risk with Covid 19 or the Corona Virus. The more items the bigger the risk.
We repair sewing machines and other appliances for other people. How to mitigate these viral risks was keeping me awake. Then as my subconscious worked over this dilemma I drew on prior projects. What if I could build a compartment with reflective walls and germicidal ultraviolet lights.
Having never seen a germicidal light I got on Google, eBay and instructables. First was to find a light, eBay had a $23 pair of led bulbs with medium base screw sockets. Now a friend came over needing face masks for his employees. I told him about my project and we traded 20 sewn face masks for two rolls of reflective mylar bubbles. The quickest way to make a box was to use an old metal cart. Like many of my projects there were many failures and bad decisions before success.
Metal cart, mylar bubbles, scrap aluminum, wire, two light sockets, old darkroom timer, UV bulbs, magnets, strip of steel, tape, black out fabric sewing machine and hand tools.
Step 1: Making Cart Into Reflective Box
Adjust the 3 shelves so the lowest shelf is as close to the bottom positioned an inch away from the middle shelf. Place the top shelf as high as possible.
Wrap and tape the mylar around the cart such that the largest opening will fold up giving access into the cart.
To prevent light leakage around the door opening sew a cover out of black out curtains. I draped the fabric over the top and down both sides. Then fold over the corners at an angle and pinned. Sew along this line to create square corners. Sew a second one that will overlap the first. This allows you to tuck in the black out curtain with and the overlap prevents all light leakage.
Step 3: Magnetiz
Using clamps position a strip of packing tape the width of the door sticky side up. Position a rare Earth magnet every couple of inches on the tape in a straight line. Unclamp the tape and stick to the lower edge of the door.
For the sides of the door you can take advantage of the perfectly placed magnets you already arranged. Take another strip of tape and clamp it sticky side up on top of the earlier magnets. Now it's easy to add magnets as they alliagn with the prior magnets and stick to the tape. Turn the tape so the sticky side faces out as you place the magnets on the vertical poles. As you hinge down the door the tape will stick to the door. Repeat this process on the other side of the door.
Step 4: Wiring
To support the lights drill holes in the bar to mount the sockets one third of the way from each side. Extra holes are drilled to tie the cords out of the way and to cable tie the bar to the rack.
Step 5: Timer
To control the amount of time to expose the carts contents I used an old dark room timer from the 1960's. I added an internal socket with an led bulb and a red lens to indicate when the power was on in the box. This is not necessary but does give an extra level of protection for the operators. I put a layer of cardboard on the top to protect the fabric since any flat spot becomes a shelf to store stuff on.
Step 6: Testing Failure
After building the cart I waited for 3 and half weeks for my bulbs. Then I excitedly began to test it. UVC is powerful and dangerous when exposed to your skin and eyes. The bulbs I ordered claimed they generated 30 times more UVC than exposure to the sun. Fifteen minutes with one bulb would disinfect a 500 square foot room. This was designed with overkill with two bulbs in a small area it would have 400 times the power to disinfect.
IT WAS A LIE.
I first tested it with newspaper, I knew how it would become yellow in the sun in just a day. I cut strips and exposed them at different times. Despite my best effort to see the more exposed strips damaged, they all looked the same. Then I took a loaf of fresh bread and cut it into slices and wiped each slice on the dumpster next door. I then bagged and labeled each slice and exposed it for different times. They all molded the same.
NO DIFFERENCE. .
I consulted with my daughter the scientist and in the mail arrived a stack of 10 Dosimeter cards. These are used in hospitals to measure proper UVC doses to clean a surgery suite.
It was clear the LED bulbs from eBay were fake. They were just black light (UVA) and not germicidal (UVC) bulbs.
Step 7: More Disappointment
I filed a complaint with the seller and order a more expensive $35 bulb. This also came from an eBay seller. These bulbs were quartz glass which also generate ozone. That was not my first choice as it requires the cart be in a well ventilated area when in use. It does provide an extra lethal dose of O3 gas which will permeate around areas not in direct contact with the light.
This project has now stretched into the second month. I was delighted at how fast the new bulb came but shocked that the post office damaged it in shipment. Back to eBay for another bulb and since it was wired for two I order two bulbs for an extra $70.
Step 8: Success
Success is sweeter when it does not come easy. The new bulbs worked. I began exposing the Dosimeter cards at different times to find when would they reach a safe kill level. In six minutes the card had turned the darkest color indicating 100 micro joules per square centimeter. I decided to go with 8 minutes for a little extra protection.
Now I wanted to know if you could sunburn a banana if you had run out of cards. The answer was no. Nor did the newspaper yellow in 8 minutes. I did a test with a card face down so only reflected light would hit it. What would darken the card in 6 minutes took two hours of reflected light.
I am pleased with the contraption now I need to develop a protocol for staff. It does seem to work on killing odors but I plan to do more experiments with that. Stay safe and if you build one I would like to hear how it works for you. Thank you.