Fire classes - Extinguishers rated by class in order to be safe for the user to use
A - ordinary materials - wood, paper, etc
B - flammable liquids or things that behave like them - some plastics, etc
C - electrically energized equipment - IF power is fully removed, the fire changes to another class
D - metals - magnesium, aluminum, exotic metals - metal fires can explode if the wrong agent is used.

extinguishers carry a numeric value to indicate the size of a fire that can be extinguished with an experienced user - used for relative size
A - 1 = 5 gallon pail of water
B - equals the square footage of liquid puddle that can be extinguished.
C - no rating - these extinguishers usually carry a B rating as well.
D - square inches I think - seldom needed

ABC rated dry chemical is most common - Example - what we call a "10 pounder" weighs about 9 t0 9-1/2 pounds stands about 15" tall and about 4-1/2" in diameter is rated 2-A, 10-B,C.

This is the minimum size I would advise people to buy - Smaller ones are better than nothing! They make some decent small ones for boats.

ALL agents other than water will NOT put a fire out forever - they inhibit flames, but do NOT absorb heat, hence the ingredients - Oxygen, Heat, Fuel still exist in the fire zone, often causing reignition. Water is dangerous on B, C, and D fires.

Dry chemical can be seen, while halon, CO2, etc cannot. The gasseous agents need confinement to work well.

Any extinguisher in a car should be mounted in a metal bracket. In the mid sixties, our Fire Chief ws killed by a CO2 extinguisher in an auto accident!
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96 855R, 95 855,854, 90 744 Ti - 325,000 miles driven