Metal Powders are extremely flammable and very difficult to extinguish once it is burning.

[youtube=http://www.youtube.com/watch?v=Kk-_aiCbzI8]

Below metal powders are considered as dangerous goods by transport regulations.

Aluminium powder, coated
Hafnium powder, wetted with not less than 25% water
Titanium powder, wetted with not less than 25% water
Zirconium powder, wetted with not less than 25% water
Pyrophoric alloy or pyrophoric metal, n.o.s.
Aluminium powder, uncoated
Aluminium silicon powder, uncoated
Magnesium powder
Zinc ashes
Zinc dust or zinc powder
Barium alloys, pyrophoric
Zirconium powder, dry
Zirconium, dry, sheets, strip or coiled wire
Hafnium powder, dry
Titanium powder, dry

Titanium sponge powders
Metal catalyst, dry
Magnesium granules, coated, particle size not less than 149 microns
Cerium, turnings or gritty powder
Aluminium smelting by-products