Air pressurized water (APW) is a substance used in common fire extinguishers known as APW extinguishers. It is most often seen in residence halls and businesses where there are no computers or chemicals. Air pressurized water is nothing special; it is just water and pressurized air combined to build a more powerful stream of water, much like in high-powered squirt guns. While APW extinguishers are common, they can only be used on Class A fires. When used on other fires, these extinguishers will actually make the fire worse.
APW extinguishers are the most common type of extinguisher used. The air pressurized water contained within them is nothing special, though, and they are really little more than large squirt guns. To make air pressurized water, the extinguisher is filled two-thirds with water, while air fills the other one-third. Both the water and air are normal; there are no special additives. Using pressurized air ensures the water will stream forward when needed for firefighting.
There are four classes of fire: A, B, C, and D. A involves common combustible material such wood and paper; B is for liquids such as gasoline; C indicates an electrical fire; and D indicates a chemical fire. Air pressurized water is only useful for Class A fires, which are the most common fires in households, businesses without chemicals and large numbers of computers, and residence halls. If an APW extinguisher is used on any of the other three classes, it can make the fire worse by splattering the fire or liquid, or by conducting the electricity into the extinguisher.
APW extinguishers are often used on or near electrical equipment when a computer catches fire or material near a computer combusts. These extinguishers can be used if a Class C extinguisher is not available. Before using air pressurized water, the equipment must be unplugged and several minutes must pass before the power is completely drained from the equipment. If the extinguisher is used before unplugging, the electricity will conduct into the extinguisher, causing it to explode or cause injury to the operator.
To fight a fire, an extinguisher’s substance must be able to reduce one or more aspects of the fire triangle, a diagram that displays the three aspects of a fire. Those aspects are air, heat and fuel. Air pressurized water kills fire by reducing the heat aspect of a fire, cooling it until the fire is gone.