Halon at very high temperatures - um, phosgene, no? Just a little bit poisonous. Halon works well on flames as it is inert and heavier than air. In the case of incendiary Magnesium, Titanium e.g., a bucket of sand is a better way to go. Early Teflon (tm) research by duPont killed at least one scientist when the fry pan under test got a bit too hot. According to the legend.