Dust explosions

This is demonstration that I've done in class dozens of times. It's great because it's hugely impressive - fireballs and all that - but actually involves pretty low risk if you know what you're doing.

The lycopodium powder is flammable, but in piles it's very tough to catch on fire. There's just not enough oxygen to get to each of the tiny grains of powder.

When the same powder, however, is suspended in the air, the oxygen can very quickly get to each of the grains, resulting in an instant and thorough reaction.

Good stuff - and highly relevant when you see stuff like the video at the bottom, of a grain elevator explosion in Evendale, OH, about three miles from my school.