Here at Nukit, we do a fair amount of R&D, and while much of it comes to nothing, sometimes it's an interesting sort of nothing worth writing about.
Recently we did a deep dive on CLO2, aka Chlorine Dioxide, an active ingredient in various dodgy products pushed early in the pandemic before they were widely exposed as a scam. We wanted to see if there was a tiny bit of science at the root of it all and if anything might come of it.
We're only going to talk about CLO2 gas as an airborne mitigation - but some people ingested it - which is a terribly bad idea. There is zero evidence that if ingested, injected, etc., it will do anything but harm you and then eventually kill you in a really painful way.
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However, CLO2 is still sold - and is quite popular in some countries as a mitigation against airborne pathogens. It relies on the old "Bubble of Protection" marketing scam, aka the "air is Jello" cognitive fallacy.
The "Bubble of Protection" pitch suggests to consumers that they can treat just the air immediately around themselves and that air will somehow (perhaps through previously undiscovered laws of physics) cling to their heads and follow them around or stay still and motionless while they sit, providing a steady 10 liters per minute of clean air that somehow does not mix with the rooms ambient air (possibly via wizardry, we respectfully hesitate to speculate on phenomenon so far outside the range of known science).
Consumers find this idea far more appealing than the obvious reality where air is a fluid, constantly swirling around us, mixing with all the air in the room like cream in coffee, and there's no way to keep it separate, have it politely stay in one place or follow our heads around snobbishly refusing to mix with "dirty" air. "Bubble of Protection" marketing is still quite common- and still unrealistic.
CLO2 is sold in a variety of form factors - wristbands, badges, pens, glowstick-style pendants that clip onto your pocket, air freshener canisters. All claim that they will slowly release chlorine dioxide into the air and protect the area around the user from pathogens.
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Now, like most of these things, the claims aren't made out of thin air, there are official looking certifications, and quite a few studies presented that seem to support their claims that chlorine dioxide gas really does mitigate airborne pathogens.
Protective effect of low-concentration chlorine dioxide gas against influenza A virus infection.
Roughly speaking, from the data we have, the dose required to have a reliable effect on a wide range of airborne pathogens is 0.1 ppm (0.3 mg/m³). Unfortunately, this is also the NIOSH limit for long-term exposure. So 0.1 ppm (0.3 mg/m3), no higher, no lower - it's a tiny, tiny window of efficacy versus safety.
As with all safety evaluations, we need to be able to measure what we are evaluating. So we're using one of these:
This is a fantastically well-designed little device that resolves down to 0.1 ppm, but flashes and beeps at 0.3 ppm - the NIOSH limit for safe exposure for 15 minutes. (We wore a respirator during testing of course, 3M 60926 cartridges are inexpensive, work well against CLO2 and most other common threats, so should already be part of everyone's emergency kit.) The Honeywell is not research lab accurate - but safety accurate, which is good enough for what we do.
Like GUV, once you have a good gauge and some appropriate PPE, CLO2 is pretty easy to safely work with - but without means to accurately measure what you are managing, you are really flailing around in the dark and wasting everyone's time. There's no way to make a meaningful safety assessment of a given product if you can't verify the manufacturer's claims.
All of the CLO2 personal protection products we have tested basically work by the same mechanism - a two-part reaction of powder and liquid (usually water) produces a gel that slowly releases CLO2 over a period of days or weeks.
Different companies stabilize the solution in different ways, the mechanics vary, but usually a capsule is broken in another container to start the reaction, but the basic chemistry is the same.
We put the different products in a sealed plastic box to test the reaction and the sensitivity of the meter, then in a small bathroom with the vents turned off, and then in an office.
The problem with all of these scenerios turned out to be maintaining the very precise concentration required entirely through a one-time chemical reaction. The CLO2 gas disperses easily and instantly. If all the doors and windows are closed - you go past the safe 0.3 ppm limit. If you even crack a window open to lower it, you immediately drop below the effective level of 0.1 ppm (0.3 mg/m³).
Proximity to the source of the gas matters very little, it would do nothing outdoors or in a large room but dissipate instantly. Even in a small room, it's basically impossible to stay in the optimal 0.1 ppm range.
The only way we can think of to do it is with a feedback loop using a CIO2 sensor that constantly opens and closes a servo controlled valve in a container to release the CLO2 into the air to maintain optimal levels. But we can't really see a reason to do this instead of using Far-UVC - other than cost and the fact that it can penetrate when UV cannot. For penetration and gassing of unoccupied spaces, ozone is easier to produce, cheaper to measure, and has most of the same advantages and disadvantages. Even for surface disinfection, HOCL is much safer and just as effective.
So CLO2 is interesting, but so far not at all useful for consumers and likely too dangerous to be worth the trouble at effective levels. We suggest you give it a pass.