The Science of Thermal Fogging

The concept behind using a thermal fogger to disperse chemical weapons is known as pulsejet technology, which is indeed a jet propulsion method. For the purposes of thermal fogging, the chemicals are heated to ~1400 degrees Celsius (C) in a combustion chamber and the fogger uses airflow to push the chemical mixture out a long nozzle resonator that cools the fog to 100-500 C before it is blown out as fog that cools as it hits air.


B/W image drawing with text from an old white paper book. The text says FOG DISSEMINATION at the top then a paragraph with `Fog dissemination devices operate by rapidly vaporizing a high boiling point liquid agent formulation. This is accomplished by injecting the liquid agent into a hot gas flow and allowing the vaporized agent to contact the cooler ambient air where the agent condenses into a fog and ultimately into extremely small agent particles.` In the middle is the drawing with a square on the left with a long rectangle coming out of it to the right with a cloud out the further end of the rectangle. There are bits of text around it, pointing to the box it says `FUEL`, `SPARK`, and `COMBUSTION CHAMBER`. in the middle of the rectange it says `HOT GASES` in the middle of arrows pointing out towards the cloud. Along the rectangle another injection area is noted for `Liquid Agent Injection` Text on the bottom says `FIGURE 4. FOG DISSEMINATION. A liquid chemical agent is vaporized by a hot gas flow and released as a fog cloud`.

Figure 41: Concept drawing from the International Association of Chiefs of Police chemical agents manual (Crockett 1969).


Although the mixture does cool considerably from its peak temperature before being released, the chemicals were heated to such high temperatures that they will thermally decompose, creating a much more toxic mixture of gasses. Indeed, the thermal cracking temperatures of CN gas (248 C Compton (1987)), CS gas (450 - 550 C; Xue et al. (2015)), Oleoresin Capsicum (OC) gas (< 200 C; Henderson and Henderson (1992)), and Terephthalic Acid (TPA) smoke (445 C; Kimyonok and Ulut├╝rk (2016)) are well below the temperatures achieved in a thermal fogger.

As a result, it is impossible for anyone to definitively know what chemicals they are fogging someone with, but it is fair to say the mixture is likely to have considerably higher toxicity than product labels and safety data sheets indicate.