A fire extinguisher; an active fire protection device used to extinguish or control small fires, usually in an emergency. Not intended for use on a raging fire. A fire extinguisher consists of a hand-held cylindrical pressure vessel containing an agent discharged to extinguish a fire. Fire extinguishers made with non-cylindrical pressure vessels also available, but they are less common. Nitrogen commonly used in dry chemical extinguishers, whereas air commonly used in water and foam extinguishers. The most common type stored pressure fire extinguishers. The expellant gas contained in a separate cartridge punctured prior to discharge, exposing the propellant to the extinguishing agent.