"Chemists are hypersensitive to the phrase 'toxic chemical.' Anything in excess is toxic (people can drown in water). So when I saw 'toxic halon gas' in your column, I was taken aback. Yes, Wikipedia says 'toxic,' but let's be a little more subtle here.
The reason halons were chosen as fire extinguishers is not only because they work well but also because they are quite unreactive. Halocarbons are used for synthetic blood and for cardiac imaging contrast agents (a use to which they have been put for yours — truly three times in the last six months, and I still seem to be here). So saying 'halons are toxic' is about as enlightening as saying 'music is loud.' Well, some music is loud. Sometimes that loudness is intentional, and sometimes it's a side-effect of turning the volume control the wrong way.
Same thing with halons. On an acute basis, they are utterly innocuous. Some halohydrocarbons are carcinogenic (in fact, Mike Plewa at the UI has shown that some halohydrocarbons that are the byproduct of chlorinating water are some of the strongest carcinogens known. But if we don't kill bacteria in our water, there are nasty acute diseases we'd get that also killed people worldwide until chlorination became common in the 20th century. If you want to live 'til next week, chlorination is good. If you want to live 250 years, it may not be).
The ways that halons suppress fire are, first, by displacing oxygen and, secondly, by suppressing the chemical reactions active in fires. Some of the products of the latter activity are toxic, so I wouldn't want to hang around in the presence of both halon extinguisher and fire, but that's mainly because of the smoke and fumes, not because of the halon."It'd be interesting to know which UIUC chemistry professor reads the News-Gazette.