Custard powder is flammable
Minimal details to protect the guilty.

It's possible build a flamethrower using custard powder, a weedsprayer, a car battery and some wire. Blow a nice cloud of custard powder into the air over a hot wire, and if the consistency of the cloud is right, it produces an impressive fireball six or eight feet across.

Top tip: not all the powder burns. Some of it settles on the ground. If, as you are playing with your flamethrower, you walk around, this is not a problem. If you stop moving and do three or four "burns" in one place, a decent sized layer of fuel will build up directly in front of you. On the fourth or fifth burn, the slight breeze generate by the fireball will disturb the layer you've made and you will experience the joys of a secondary dust cloud explosion. These can be surprisingly violent and damage trousers.
(SonofRojBlake, Fri 10 Aug 2012, 8:37, 3 replies)

Quite a lot of powders burn.
Basically anything that is organic, and a fine powder, will explode under the right conditions.

Part of my work involves loading terminals at ports. In the course of my career have seen several grain terminals go up, usually dust from wheat or corn, and for the really big bangs what you want is a sugar terminal.

We built one in France. To get into it you had to empty your pockets and wear a special non static suit, and a hat that stopped you touching your hair, which could in theory produce a spark.

Oh, I beleive coal dust goes up well too. Never seen that though.
(username failed moderation, Fri 10 Aug 2012, 9:14, closed)

And some metal powders (e.g. iron and zinc) can spontaneously ignite in air.

( The Mock TurtIe ™ --- Thinks you are a cunt, on, Fri 10 Aug 2012, 20:43, closed)

"These can be surprisingly violent and damage trousers."
Quite possibly from the inside..
(BeatsWork, Fri 10 Aug 2012, 9:49, closed)