fire extinguisher

Three different kinds of fire extinguisher. The water fire extinguisher is the most commonly used but it is suitable only for fires of ordinary combustibles, such as wood, paper, some plastics, and textiles. It is dangerous to use around electrical equipment. The carbon dioxide fire extinguisher needs to be used at close range and will extinguish fires of flammable liquids, such as oil, petrol, and paint. It works by starving the fire of oxygen. Carbon dioxide fire extinguishers are also used for fires involving electrical equipment. Dry chemical fire extinguishers are effective on most common types of fires but the powder is corrosive and it leaves a sticky residue.

Device for putting out a fire. Fire extinguishers work by removing one of the three conditions necessary for fire to continue (heat, oxygen, and fuel), either by cooling the fire or by excluding oxygen.

The simplest fire extinguishers contain water, which when propelled onto the fire cools it down. Water extinguishers cannot be used on electrical fires, as there is a danger of electrocution, or on burning oil, as the oil will float on the water and spread the blaze.

Many domestic extinguishers contain liquid carbon dioxide under pressure. When the handle is pressed, carbon dioxide is released as a gas that blankets the burning material and prevents oxygen from reaching it. Dry extinguishers spray powder, which then releases carbon dioxide gas. Wet extinguishers are often of the soda-acid type; when activated, sulphuric acid mixes with sodium bicarbonate, producing carbon dioxide. The gas pressure forces the solution out of a nozzle, and a foaming agent may be added.

Some extinguishers contain halons (hydrocarbons with one or more hydrogens substituted by a halogen such as chlorine, bromine, or fluorine). These are very effective at smothering fires, but cause damage to the ozone layer, and their use is now restricted.