P.A.S.S. is an acronym used to describe the actions taken to properly use a halon, dry chemical or carbon dioxide fire extinguisher. It stands for Pull, Aim, Squeeze and Sweep, the four steps to successful fire fighting.
Pull. "P" stands for "pull," and it refers to the locking pin on the handle. The pin is used to prevent the fire extinguisher from being discharged accidentally. In order for the lever to work, the pin must be removed.
Aim. "A" stands for "aim." If the fire extinguisher discharges from the end of a hose, point the hose at the base of the fire. If your extinguisher discharges from a nozzle at the top of the canister, point it directly at the base of the fire. P.A.S.S.-style fire extinguishers discharge only for about 10 seconds, so it's important to aim first so you don't waste your extinguisher.
Squeeze. The first "S" in P.A.S.S. stands for "squeeze." Once your extinguisher is properly aimed, pull the lever upward toward your palm.
Sweep. Sweep the nozzle side-to-side toward the base of the fire to make sure all potential hotspots are saturated. Don't hesitate to use the extinguisher until it is empty.