I have a good friend who sells, and fills fire extinguishers. He has lots of out of date units that we sometimes do unscientific testing with.
There are several things you learn very quickly:
Those 2.5 lb dry chemical extinguishers might make you "feel" safer, but your not going to put much of anything out with one.
The smallest dry chem extinguisher worth having is a 10 pounder.
There is no such thing a too big. It's only too big, if your too old to grab it, and run with it.
The instructions for a fire extinguisher all leave out one important step, HOLD BREATH. If you don't take a deep breath, and hold it, you will probably inhale some of the contents, and you will regret it.
Get in close. If you don't have a 400 lb. Ansul, your only going to have a number of seconds to put out the fire. If your not right up in it, you may as well throw the empty bottle on the fire, and go get some marshmallows.
If you simply cannot fit a 10 lb. extinguisher on, or in the area you want to protect, the only small extinguisher you can really put out a fire with is a halon unit. You can't get "real" halon anymore, (thanks EPA), but there are environmentally friendly halons out there now, that work. The problem here is they all cost well over $100.
Halon is so effective, you can put out a candle on one end of in your living room, standing on the other end, facing the wrong way, with about a one second blast of a halon extinguisher. Halon is a gas, so it is going to be effected by winds, when you use it outdoors.
A really hot fire, like an engine fire, is best put out with water. Anything else may work, but the fire can keep reigniting from the heat, and your probably not going to have a big enough extinguisher to keep putting it out. I discovered this on the highway last year, trying to help a motorist.
