Class “A” fires

Class “A” fires are defined as ordinary combustibles. These types are fires use commonly flammable material as their fuel source. Wood, fabric, paper, trash, and plastics are common sources of Class A fires. … Water is the most common extinguishing agent, but others such as dry chemical, halon and foam can be used effectively.

Class “B” Fires

A Class “B” fire involves flammable liquid or gas. Familiar examples would be gasoline, oil, propane, and natural gas. A variety of fire extinguishing agents are used on flammable liquid fires employing all theories of fire extinguishment. Which agent is best to use is dependent upon the circumstances involved. Flammable liquids do not ignite in their liquid state, rather it is the vapors being generated by these liquids that ignite. The mixture of oxygen and flammable vapors in proper proportion needs only an ignition source to start the combustion process.

Class “C” Fires

Class “C” fires involve live electrical equipment and require the use of an extinguishing agent and/or extinguisher that will not conduct electricity back to the fire fighters. Electricity is an energy source and an ignition source, but by itself will not burn. Instead, the live electrical equipment may serve as a source of ignition for a class “A” fire such as insulation or packing, or a class “B” fire.

Class “D” fires

Class “D” fires involve exotic metals such as titanium, zirconium, magnesium, and sodium. These fires require special agents such as dry powders and special application techniques. The extinguishing agents and techniques used on “A”, “B”, or “C” fires will not work on class “D” fires, nor will the agents and techniques used for class “D” fires work on any other classification of fire. Many common agents like water will actually react to burning metals and increase the intensity of the fire in a violent manner.

Class “K” Fires

Class “K” fires involve cooking media such as oils and grease commonly found in commercial kitchens. These can be any animal or vegetable based fats or oils. These extremely hot fires require special agents such as wet chemical extinguishers and systems that are alkaline in nature and have superior cooling capabilities because of the danger of re-flash. The entire mass of the cooking medium in a deep fat fryer must be secured and cooled below its auto-ignition point in order to achieve complete extinguishment.