Trialing Far UVC and Glycol Vapors

As we go into winter, we're thinking about infection reduction.  Our primary approaches are requiring high-filtration masks at half our dances (which we'll run another survey on in early Fall) and bringing in large amounts of outside air, but we're interested in exploring a variety of options.  Two promising candidates are far UVC and glycol vapors, and we'll trial both at our September 7th dance.

This is primarily a logistical test: we won't be able to tell whether these are working for pathogen control (that's what the studies linked below are for).  Instead, we're trying to get a sense for how well these fit our particular space, and how practical they would be for regular use.

Far UVC

Ultraviolet light is a spectrum, shorter wavelengths just beyond visual range.  The effect of light on viruses, bacteria, and the human body depends very strongly on wavelength, and some kinds of UV are dangerous for humans.  The specific range of UV light we'll use, however, is the much safer "far UVC" (~222nm).  The risk here is low: with such a short wavelength this light is absorbed by the outer layers of dead skin and the tear film of the eyes, without penetrating deeper the way longer wavelengths do.  See Görlitz et al. (2023) which reviews the risks and benefits of far UVC for pathogen control and concludes that "current evidence supports using far-UVC systems within existing guidelines."

We'll be setting up one Aerolamp, which is built around a Ushio Care222 Filtered Far UVC Module (test report).  This is a filtered krypton-chloride lamp, which produces 100mW of UV, of which >99% is far UVC.  It will be on stage, aimed horizontally outwards to clean the air above people's heads.  If we decide to go further with this method we plan to use four lamps, one in each corner of the hall, putting out a total of 400mW (still well within safe exposure limits).  When we run our Spark in the Dark dances each of our blacklight fixtures puts out more than ten times this much UVA (~10W each).

One downside of this kind of lamp when used in small well-sealed rooms is that they produce low levels of ozone.  In our case, however, the room is large enough that the effect would be negligible.  Additionally, since we're bringing in >10k CFM of external air with our two 42" barrel fans, even this negligible amount will quickly be exhausted.

Glycol Vapors

In the 1940s researchers learned that glycol vapors are surprisingly effective at inactivating airborne pathogens.  For example, Harris and Stokes (1943) ran an early controlled experiment and found a large reduction in respiratory infections in a children's skilled nursing facility.  Unfortunately this early work was essentially forgotten as public health shifted focus, and it wasn't until COVID that people began to take glycol vapors seriously for pathogen control: Gomez et al. (2022), Styles et al. (2023), Ratliff et al. (2023), Sultan et al. (2024), and Desai et al. (2025) all found high levels of pathogen inactivation with glycol vapors.

In the meantime fog machines have become widespread in entertainment, putting out much higher vapor concentrations than required for pathogen inactivation, and the risks have become better-studied.  In 2003, the EPA looked into the research and concluded "that there is a reasonable certainty no harm will result to the general population or any subgroup from the use of triethylene glycol."

We'll be setting up a small fog machine, ultrasonic humidifier, or aromatherapy nebulizer by the inward-pointing barrel fan, and we'll use triethylene glycol for fluid.  We'll have it on a low setting and aim to put out a little under 60mL over the course of the event and keep the air at around 1mg/m3.  While this is a very low level, well below where it would produce visible fog or where most people could smell it, it's high enough for pathogen inactivation.