Fire Extinguisher

A fire extinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations. It is not intended for use on an out-of-control fire, such as one which has reached the ceiling, endangers the user (i.e. no escape route, smoke, explosion hazard, etc.), or otherwise requires the expertise of a fire department. Typically, a fire extinguisher consists of a hand-held cylindrical pressure vessel containing an agent which can be discharged to extinguish a fire. There are two main types of fire extinguishers: Stored pressure and generated pressure. In stored pressure units, the expellant is stored in the same chamber as the firefighting agent itself. Depending on the agent used, different propellants are used. With dry chemical extinguishers, nitrogen is typically used; water and foam are pressurized with air. Stored pressure is the most common type of fire extinguisher. Cartridge-operated extinguishers contain the expellant gas in a separate cartridge that is punctured prior to discharge, exposing the propellant to the agent.

The modern fire extinguisher was invented by British Captain George William Manby in 1818; it consisted of a copper vessel of 3 gallons (13.6 litres) of pearl ash (potassium carbonate) solution contained within compressed air. The soda-acid extinguisher was first patented in 1866 by Francois Carlier of France, which mixed a solution of water and sodium bicarbonate with tartaric acid, producing the propellant CO₂ gas. A soda-acid extinguisher was patented in the U.S. in 1881 by Almon M. Granger. His extinguisher used the reaction between sodium bicarbonate solution and sulfuric acid to expel pressurized water onto a fire.

The chemical foam extinguisher was invented around 1905 by Alexander Laurant of Russia, who first used it to extinguish a pan of burning naphtha. It works and looks similar to the soda-acid type, but the inner parts are different. The main tank contains a solution of water, foam compound (usually made from licorice root) and sodium bicarbonate. A cylindrical metal or plastic chamber holds about a quart and a half of 13% aluminium sulfate and is capped with a lead cap. When the unit is turned over, the chemicals mix, producing CO₂ gas. The licorice causes some of the CO₂ bubbles to become trapped in the liquid and is discharged on the fire as a thick whitish-brown foam.

Fire extinguishers are typically fitted in buildings at an easily-accessible location, such as against a wall in a high-traffic area. They are also often fitted to motor vehicles, watercraft, and aircraft - this is required by law in many jurisdictions, for identified classes of vehicles. Under NFPA 10 all commercial vehicles must carry at least one fire extinguisher (size/UL rating depending on type of vehicle and cargo (i.e.. fuel tankers typically must have a 9.1 kg (20 lb). when most others can carry a 2.3 kg (5 lb).) The revised NFPA 10 created criteria on the placement of "Fast Flow Extinguishers" in locations such as those storing and transporting pressurized flammable liquids and pressurized flammable gas or areas with possibility of three dimensional class B hazards are required to have "fast flow" extinguishers.