Originally Posted by
UncleFrosty
Dry Chem extinguishers break the chemical reaction that leads to flame, so any breeze or anything that breaks the powder coat etc can impact on the effectiveness of these significantly (demonstrated when used on pooled fuel fires - re-ignites easily when powder layer on surface is broken). They don't remove any heat as such, so water works better on grass fires under vehicles.
The ratings on the side of the extinguisher indicate it's usefulness in each type of fire:
A - solid fuels (eg grass/wood)
B - liquid fuels (eg diesel)
C - gas
D - combustible metals (eg magnesium)
E - electrical
F - fat/oil (eg deep fryers)
The higher the number next to each letter the better it is at extinguishing that fire.
DC is a good All-rounder. Water way better for combustible solid fires due to its heat-removing properties. Foam for fuel, CO2 for electrical.
Big cojones for C, D or F class fires...