Metal powder barge fires (related)

Does anybody know why, when you get down to five- and ten-micron powders, they're a problem?

Student: Breathing them in.

Yeah, but before you even breathe them in, they tend to be pyrophoric. There's enough surface area that they burn really well. You've seen a metal powder fire — you've been to fireworks demonstrations, you've seen incendiary flares. That's nothing more than a metal powder fire. Or you've seen rockets take off — a solid rocket motor, that's a metal powder fire. You get small fine metal powders, lots of surface-to-volume ratio, heat them up a little bit, and you get some really good fires.