When a fire breaks out, you need to act quickly. The best way to do that is by using a fire extinguisher. There are different types of fire extinguishers and each type is rated for a specific class of fire. Each class of fire is characterized by the kind of material or substance that is burning.
There are four classes of fires: Class A – ordinary combustible materials such as paper, wood and cloth; Class B – flammable liquids such as gasoline, kerosene and oil; Class C – energized electrical equipment (motors, appliances, power tools); and Class K – combustible fats and oils in cooking appliances.
Each of these fires requires a different kind of extinguisher and can be put out with a variety of chemicals. These include water, dry chemical, carbon dioxide and clean agent solutions.
Handheld fire extinguishers are kept in a pressurized cylinder, usually made of metal, and have a handle on the top. The user activates the fire extinguisher by pulling a pin at the bottom of the unit and depressing a lever or knob on the cylinder. This causes a valve to open and allows the fire-suppressing solution to flow out the nozzle.
These extinguishers use either potassium acetate, potassium carbonate, potassium citrate or a combination of these chemicals. They are nonconductive and do not leave a residue, making them suitable for use on electrical fires. They also can be used on Class A fires, but not on combustible metals.
Another type of handheld fire extinguisher uses pure carbon dioxide. It is kept in a pressurized liquid form in the cylinder and when the fire extinguisher is discharged, the gas expands to displace oxygen around the flames, which effectively puts the fire out. This type of fire extinguisher is popular for use in restaurants because it does not damage or contaminate the cooking equipment or food.
Other handheld fire extinguishers use a clean agent solution such as a mixture of sodium bicarbonate, water and silica gel particles. These are effective on Class B fires because the sodium bicarbonate interrupts the chain reaction of the fuel and the silica gel absorbs the unburned fuel, preventing contact with air and allowing it to be vaporized by the water. This type of fire extinguisher can be used on both Class A and Class B fires and is a good choice for electrical fires because it does not conduct electricity.
There are also portable extinguishers that discharge a mixture of foam and clean agent solutions. These are effective on both Class A and Class B fires because they create a seal over the fuel surface to prevent oxygen from reaching the flames and they are effective in freezing temperatures. Examples of these are AFFF and FFFP.
There are also cart-mounted fire extinguishers that are a more convenient way to fight large industrial and commercial fires, such as those at airport runways, docks and heliports. These can be used on either Class A or Class B fires and are able to be operated from a greater distance than handheld units.