I have sold, serviced and used fire extinguishers for a living for over 30 years.
There is a lot of disinformation out there about fire extinguishers and cars-much of it marketing hype.
As a practical matter, there are 2 basic groups of fire extinguishers commonly available: dry chemical and clean agent.
Dry chemical can be broken down to ABC (all purpose), BC and PK (rated for flammable liquids, electrical).
Clean agents come in several forms: Halon, Halotron, CO2… In the sizes usually found in cars, only have a BC flammable liquids, electrical rating.
These are my recommendations for installing extinguishers in your average collector car or truck and why:
1. BC, Purple K dry chemical 5# to 10# sizes:
Pro’s: Best agents for car fires, higher ratings, economical, will not stick and corrode to hot surfaces.
Cons: It is a chemical (sodium or potassium bicarbonate) and will make a mess.
2. ABC dry chemical 5# to 10# sizes:
Pro’s: Like BC and PK they are economical and have good firefighting capability with the addition of class A (wood, paper, plastics…).
Cons: They are a chemical (mono ammonium phosphate), will make a mess and will form a corrosive coating on anything over 350 degrees.
3. Clean agents 5#-11# sizes:
Pro’s: Clean agents do not leave any residue after use. They can put out a small, confined fire without making a mess. Particularly good for electrical fires behind dashes, interior fires…
Cons: In the sizes typically installed in cars they have a very low rating because they are gases and are greatly affected by air movement or wind… They are also very expensive to attain and recharge.
Note that I do not recommend anything under 5# in size.
You are trying to put out a fire before your car becomes a loss…right?
Don’t bring a knife to a gun fight.
There is a lot of good info here: