Introduction: Homemade UV-C Disinfection Cabinet for COVID-19 and Other Nasties
Ultraviolet (UV) light is a common way to disinfect things. It works by disrupting the DNA structure of bacteria and viruses, and preventing their replication. However, there are different types of UV and you need to use the right one for disinfection. They are:
UV-A - Used in black lights at Halloween parties
UV-B - Causes sunburns and skin cancer
UV-C - Used for disinfection. Filtered by the ozone layer so you don't see much naturally-occurring UV-C
The magic wavelength for DNA disruption is 254nm, which falls in the UV-C spectrum. Therefore, a UV-C light must be used in any disinfection application. UV-C lights are available commercially, and are often labeled as "germicidal".
By using a UV-C light combined with other commonly gettable materials, you can make your own disinfection cabinet, like I did. This instructable will show you how I did it.
This instructable was built with parts procured from Amazon (bulb, fixture) and Home Depot (cooler, velcro, aluminum foil, aluminum tape), and no power tools are required for construction.
Disclaimer: I'm not a particle physicist, but I did my best to understand and use the physics, microbiology and math behind this solution. Treat this article and its assertions with the same prosecution and diligence of anything else you find on the internet.
WARNING! UV-C lighting, while good for disinfection, is very bad for humans. Bad for your skin, bad for your eyes. Therefore, it's important to build a solution that doesn't allow the light to escape and break down your own personal DNA.
Step 1: Materials
I used the following materials, most of which I got from Home Depot:
1. Cabinet. Any cabinet with a lid that can be closed will work. I got a Rubbermaid 75qt cooler from Home Depot. Its insulating properties are useful when disinfecting groceries.
2, 3. Aluminum tape and aluminum foil. The inside of the cabinet needs to be lined with aluminum foil. Aluminum reflects UV rays; most other materials absorb UV rays. Aluminum tape is commonly used to fasten ducting in HVAC systems, and works out nicely here.
4. Velcro tape. Two 2"x4" patches. Used to attach the lamp to the lid. You can also use tape/zip-ties and other things to fasten the lamp to the lid.
5, 6. 2x paint grids and paint stirrers. It's important to raise the irradiated materials off the floor so that the bottom can be exposed to UV-C as well. I fastened two of these together to make a stand. A small metal dish rack could also work as well. I used the paint stirrers to provide some extra rigidity.
7. Zip-ties. I didn't wind up using these, but it's in the picture, so I thought I'd call it out.
Step 2: Line the Inside With Aluminum Foil
Using the aluminum foil and aluminum tape, line the inside of the cabinet.
Step 3: Procuring a UV-C Light
There are lots of UV-C lights available commercially. I wound up getting an OSRAM/Sylvania 15W tube light, which is 18 inches long. Note the "Germicidal" labeling on the bulb. This light has the standard 2 pin connector that is common with tube lights. Other form factors and implementations are out there and are equally as feasible.
I figured I would go to Home Depot and buy a tube light fixture for this bulb. However, I found out the hard way that the standard sizes for tube lights are 24" and 48". My light is 18". Fortunately, I was able to find an 18" tube light from a pet store, that is typically intended for illuminating your pet lizard. This lamp comes with a UV-B bulb, which is good for your lizard, but no good for this project. It was an easy bulb swap. There's a plastic cover for the bulb, which I removed and discarded.
Step 4: Fastening the Lamp
I used a 4"x4" patch of velcro to attach the lamp. It worked nicely, since the lamp is 4" wide. I put the velcro patch in a spot that allows the UV-C tube light to be centered on the lid. After attaching the velcro, I lined the rest of the lid with aluminum foil.
Step 5: A Rack to Lift Your Items
It's helpful to get the items you want to disinfect off the floor, so that the bottom can be hit with UV-C rays as well. I taped together 2 paint trays to make a rack. I broke off pieces of the paint stirrer and used them to add a little extra rigidity.
Step 6: Final Assembly and Ready to Disinfect!
At this point, all that's needed to be done is attach the lamp! This was trivial, given the velcro connection. At first I thought I might need to cut a notch to account for the power cord, but the lid is able to sufficiently close without any surgery.
You can see a photo of the lamp in action. (I used the timer on my phone to take the photo, to avoid zapping myself with UV-C)
Important Note: Since taking this photo, I've read a number of articles that advise against using UV-C disinfection with N95 masks, because the UV-C can break down the elastic. So I largely use it to disinfect groceries and takeout food.
To use the cabinet, put your stuff in (while the lamp is off!), close the lid, and then plug in the lamp. That's it!
Only one question remains: how long should I have my stuff in the cabinet to get proper disinfection? The answer depends on: the wattage of your bulb, the desired amount of irradiation energy needed to achieve disinfection, and the distance from the bulb to the item(s) you are disinfecting.
The UV-C bulb is a 15W OSRAM 21259 G15T8/OF
The bulb is rated at 15W, but that’s the power consumed, not the UV power emitted. OSRAM doesn’t have a spec on UV power output. However, another manufacturer of a very similar bulb, USHIO, does spec this at 4.9W.
USHIO 3000007 G15T8: https://www.ushio.com/files/specifications/germic...
Anywhere from 7 J/m^2-241 J/m^2 (average 67 J/m^2) D90 dosage is required to kill coronaviruses. Source: https://www.uv-light.co.uk/coronavirus/
Here’s the math that I did to calculate UV dosage time. You should do your own math and follow your own conclusions.
A G15T8 (15 W germicidal fluorescent bulb) emits 4.9 W of UV-C with a central peak at 253.7 nm
UV Dose = UV_Energy/Area
UV_Energy = UV_bulb_power*Exposure_time
Area = 4*pi*(UV_bulb distance^2) [assuming spherical divergence]
This leads to: UV_Dose = UV_bulb_power*Exposure_time/(4*pi*UV_bulb_distance^2)
So the desired direct exposure time in seconds is:
Exposure_time = (Desired_UV_Dose*4*pi*(UV_bulb_distance^2))/UV_bulb_power
Units: UV_Dose: Joules/m^2, UV_Energy: Joules, UV_bulb_power: Watts, Area: m^2, UV_bulb_distance: m, Exposure_time: s, pi: 3.141592
The distance from the bulb to the cabinet floor is 29cm (or 0.29m). For UV_Dose, I’m using the highest number from the studies referenced above. This gives:
Exposure time = ((241 J/m^2)*4*pi*(0.29 m^2))/4.9 W = 254.7 J/4.9 W = 52 seconds
I typically irradiate my items (mainly groceries and takeout food) for 2 minutes for good measure.