Types of Fire Extinguishers
A fire extinguisher is a vital piece of potentially life-saving equipment. They are essential in most homes, schools, and businesses and should be stored in accessible areas where they can be easily accessed and used in the event of a fire.
There are several types of extinguisher available, including water, dry chemical, foam, and wetting agent. Each type has its own specific fire-fighting capabilities and should be chosen to suit the particular situation in which you are likely to find yourself using the extinguisher.
Water (class A, B, C)
The most common type of extinguisher is a water-based unit. Its operation is relatively simple. Just pull the pin, remove the hose and wand assembly, and aim the nozzle at the base of the fire, where it will extinguish it most efficiently.
Some models of water extinguishers have jet nozzles, which deliver a fine spray courtesy of high pressure. This helps to extract more heat from the burning material and also improves the effectiveness of the water. Surfactants can also be added to help the water penetrate further into the burning material, particularly when dealing with class A and C fires.
Dry powder (class D)
This extinguisher is designed to smother metal fires by isolating and smothering them with a copper or sodium chloride based dry powder. They are mounted on two wheel carts and operate in a similar manner to ABC, Halon, and Carbon Dioxide extinguishers.
They can be found in most workplaces, from large factories to small office suites and shops. They can be used on all classes of fire, except class K and C fires involving fat or oil.
In the United States, they can be purchased in various sizes and come in dry powder, water, and wetting agent types. They are a convenient and affordable option for many users and are particularly effective on Class D fires involving metals, such as iron or steel.
These extinguishers are available in many different styles and can be purchased with a variety of nozzles to meet the needs of the user. Some are a jet nozzle, while others are a spray nozzle.
Some units are also available with gauges to indicate when the pressure is too low or too high. These units should be checked monthly, and pressure tested every few years.
Dry chemical/carbon tetrachloride extinguishers are available in a range of sizes from 1 imperial quart (1.1 L) to 2 imperial gallon (9 L) capacities. These extinguishers were introduced around 1912 by Pyrene and they vapourised and extinguished fires by interfering with the chemical reaction of the fuel. The fumes from these extinguishers were toxic and can cause serious health problems when used in confined spaces.
Other dry chemical extinguishers are manufactured from a mixture of sodium bicarbonate and potassium carbonate, which form a soapy foam that covers the fuel, cooling it below its ignition temperature. This foam is most effective on class A, B, and C fires involving fuels such as cooking oils and greases or vegetable fats and animal fats.