When it is described thusly:
If Nazis find something too nasty to work with, the thing is by association, nasty. Welcome to the wonderful world of flourine compounds, specifically chlorine trifluoride.
The GURPS e-mail list had a long running gag about the uses of flaming uranium hexaflouride. Just the kind of stuff you want the kiddies to have in their chemistry sets. The great REPSLEH MIJ II has story about witnessing a flourine fire. It is the kind of disaster that bugs you in the way that a nuclear event would.