Beware of Magical Thinking on UV-C
Ralph Rathburn
Certified Scaling Up Coach | Experienced CEO | Japan Expert | International Business Owner | Occasional Baker
There has been a lot of talk about how sunlight, specifically UV-C light, can destroy the SARS-COV-2 virus that causes COVID-19. That is a real thing, and there is real science that explains how UV-C can kill the virus.
In my first piece in this series, I said I am not a doctor, but I failed to mention that I’m not a wizard like Harry Potter, either. I don’t cast magic spells; I don’t believe in magical thinking; nor do I sell snake oil, for that matter. People, by nature, LOVE to believe in magical thinking or supernatural powers to solve real-world problems, like dealing with viruses in the air, but unfortunately, it just doesn’t work that way. Sorry.
It is often reported that about 40mJ/cm2 of UV-C deactivates the COVID-19 virus. Just seeing that unfamiliar unit of measurement can confuse us enough to send us into the false magical thinking that UV-C instantly kills the virus.
This confusion is quite convenient for the salespeople who want to exploit that magical thinking to get consumers to buy stuff. Needless to say, however, it is definitely not good for the consumer.
So, let’s put aside the false magical thinking and break things down so that everyone can make informed purchase decisions.
The unit mJ/cm2 is a measure of how much light energy hits a specific spot over 1 second. The farther away the light source is from the spot, the smaller the amount of energy becomes.
Companies that install industrial UV-C disinfectant units into HVAC systems use very high-intensity UV-C bulbs and do very complex calculations on the strength of bulbs, the air speed, and how big the unit needs to be to ensure the virus gets hit with the right cumulative mJ/cm2 exposure.
Here is a very simple version of the calculations.
X mJ/cm2 * (Y m)2 ÷ (1m)2 = Z mJ/cm2
X is the mJ/cm2 of the UV-C lamp and Y is the distance from the UV-C lamp to the virus you want to deactivate. Z is the number of mJ/cm2 that actually hits the virus.
Using the Z number, we can then determine the time it takes to deactivate a specific virus or bacteria.
If the estimates of 40mJ/cm2 are correct, then 40 ÷ Z = number of seconds needed to deactivate the COVID-19 virus.
Let’s use the same equation from above with the kind of situation you might find in a portable UV-C unit.
15 mJ/cm2 * (0.1524m)2 ÷ (1m)2 = 0.348mJ/cm2
40 mJ/cm2 ÷ 0.348 mJ/cm2 = 115 seconds (divided by 2 bulbs = 57.5 seconds)
You have to hold the wand 6” away from the virus for almost 2 minutes to kill it. Magical thinking lets you believe that you just have to casually wave a UV-C wand over the virus to kill it. Science shows why it’s really important to follow the manufacturer’s instructions if you are using a UV-C disinfecting light. If you are not at the right distance or you move the light too quickly, you could end up just giving the virus a nice tan rather than destroying it!
This is why it is very unlikely that any portable air purifier can have a UV-C ‘kill zone’. Manufacturers trying to get you to believe they have one, are encouraging you to use magical thinking.
The fact of the matter is that air moves fairly quickly through most portable air purifiers. The hypothetical and yet critical question to ask is how much distance must the virus-containing air travel in order for it to be exposed to the UV-C light for 57.5 seconds. Let’s suppose that a high-end air purifier moves 380cfm (or 6.333 cubic feet per second) of air. If they outfitted the ‘kill zone’ with 2 rows of 15mJ/cm2 along its length, the answer is 57.5 sec * 6.333cfs = 364 feet.
Magical thinking lets you believe that a ‘kill zone’ that can fit in a portable air clearer will destroy the virus. Simple science shows that it won’t, unless it can be 364 feet long!
Until next time, as Jacinda Ardern the Prime Minister of New Zealand says, “Stay Safe. Be Kind.”
PS: Next time, I will talk about how the ‘detergent of the troposphere’ – hydroxyl radicals – can help clear indoor air.
NOTE: We are currently seeking professional distributors in various fields. We are also seeking independent salespeople in North America.
To learn more about how our system can help you remove viruses, bacteria and other harmful particles from your air, please download one of our brochures. Or contact me for a consultation.
- https://www.airgle.com/downloads/Brochure_AirgleCleanRoom.pdf
- www.airgle.com/downloads/Brochure_AG900Commercial.pdf
- www.airgle.com/downloads/Brochure_AG900Educational.pdf
- www.airgle.com/downloads/Brochure_AG25Ambulance.pdf
- www.airgle.com/downloads/Brochure_AG25Cars.pdf
Also, please take a look at the other articles in this series.
- https://www.dhirubhai.net/pulse/removing-scare-from-air-ralph-rathburn/
- https://www.dhirubhai.net/pulse/viral-scare-air-size-matters-ralph-rathburn/
? 2020 Ralph Rathburn