> I don't know much about fire extinguishers - I'll look for CO2.
For a long time, the basic extinguisher was water. I remember when they had hand-pumps, or acid and base in separate cups that mixed when turned upside down and forced the water out; now most seem to be pressurized.
Water is bad on electrical fires, and also for grease fires (it pushes the grease around and spreads the fire). The common alternative (and what we have at school) is "Dry Chemical", which is pretty much baking soda under pressure (really ammonium phosphate). Won't carry electricity and hardly spreads grease. But it makes a white powder mess, and if somehow that powder gets wet before the panic is over it will corrode things like electrical gear.
The long-time standard for many types of fires is Carbon Dioxide, C02. It works pretty good, won't conduct, gives little grease-spread. There is one in every commercial kitchen, often a permanent plumbed system above the fryer and grille. The CO2 is cheap but it has to be held at very high pressure. The tank is heavy and expensive, the valve has to be checked regularly and the tank re-filled. And CO2 is much less effective on wood or paper than water or dry-chemical extingushers.
If you release a large amount of CO2 in a small space and stay there, you will suffocate. But if you meet a fire which needs that much CO2, it is probably beyond safe handling. You should save your life and leave, not die trying to save property.
Plain old sand can be an effective extinguisher if it will stay on the fire. It would take too much sand to smother a couch-fire, but 10 pounds of sand might smother a transformer with relatively little mess. And sand is sometimes the only way to put out burning metals.
Halon will put out many fires at low concentration, not enough to make people sick. It had a short fad for property owners who had expensive machines and wanted the workers to hang around during the fire. Was THE standard in computer rooms. Then they realized it ate the Ozone layer. Production stopped. Many Halon systems are being decommissioned, so if you have an existing Halon system you can still get Halon that has been salvaged. Halon still makes sense in a few places: fire in a military tank in war, would you rather burn inside or go outside and be shot by the enemy? Or in the Space Shuttle.
One basic problem with Halon: the stuff is so expensive that you don't use much. Sometimes a fire will go out in a whiff of Halon, and then re-ignite, and burn the place down. So Halon normally needs a back-up. And if the back-up is any good, why have Halon?
Some of the least-poisonous of the Halon alternatives make HydroFloric Acid in a fire. This is actually seen as "good" because it encourages people to leave before worse things happen to them. But that can't be good for your gear. (Anyway you probably can't get FE-13 in a home-size bottle.)
http://www.ehs.ualberta.ca/FireSafety/index.aspx?Page=35 --READ!
http://www.h3r.com/halon/
http://www.epa.gov/Ozone/snap/fire/lists/stream.html
http://palimpsest.stanford.edu/waac/wn/wn15/wn15-2/wn15-209.html
http://palimpsest.stanford.edu/waac/wn/wn15/wn15-2/wn15-208.html
http://www.halon.org/
