How to Use a Fire Extinguisher

The different types of portable fire extinguishers available are described as follows.

Dry Chemical extinguishers are usually rated for multipurpose use ABC if they contain mono ammonium phosphate, which melts at 350° F forming a coating on the combustible surface, including wood or paper. If they contain sodium or potassium bicarbonate they are usually rated for class B and C fires.

Halon Extinguishers are often used to protect electrical equipment, Class C fires, since they leave no residue. They have a limited range, usually 4 up 6 feet.

Water extinguishers should only be used on Class A (ordinary combustibles) fires.

Carbon Dioxide (CO2) are most effective against Class B and C (liquids and electrical) fires. Since the gas disperses quickly, they are effective from 3 to 8 feet. The carbon dioxide is stored as a compressed liquid in the extinguisher; as it expands, it cools the surrounding air and it causes ice to form around the "horn" where the gas is expelled from the cylinder.

All extinguishers operate in a similar manner. Acronym PASS:

Pull, Aim, Squeeze, and Sweep

Pull the pin at the top of the extinguisher that keeps the handle from being accidentally pressed.

Aim the nozzle toward the base of the fire. Make sure you are on target - the fire extinguisher only lasts 3 to 20 seconds -

Stand approximately 8 feet away from the fire and squeeze the handle to discharge the extinguisher. If you release the handle the discharge will stop.

Sweep the nozzle back and forth at the base of the fire. After the fire appears to be out watch it carefully it might re-ignite

References:
Keller's Official OSHA Safety Handbook
Lab Safety EZ Facts: Use, Placement, Maintenance and Testing of Portable Fire Extinguishers,
http://www.hanford.gov/fire/safety/extingrs.htm#use
http://www.uh.edu/admin/srmd/usingfext.html