Types of Fires

Combustion is a chemical reaction where some sort of fuel is quickly oxidized, or combined with oxygen. This is also the process responsible for starting a fire. Three things need to be present to nourish a fire:

Oxygen or an oxidizing agent
Fuel (reducing agent)
Heat

To kill a fire, it must be lacking one of these three ingredients. Therefore, to extinguish a fire you can:

Cut off the oxygen supply.
Take away the fuel that is feeding the fire.
Cool the temperature.

Types of fires

There are four categories of fire (A, B, C, and D), each one classified based on the kind of material burning. Categories A through C use two variations of color-coded icons. The majority of fire extinguishers will be labeled with at least one of these icons in order to communicate the type of fire it should be used to battle. D fires are different in that they only have one icon associated with them because they are much rarer than the other categories.

Class A fire - sustained by materials that leave behind a byproduct of ash when they burn (e.g., paper, wood, cloth, rubber, some plastic)

Prevention
- Clear trash and clutter from storage and work areas.
How to extinguish
- Cool regular combustibles, and soak the fibers to keep them from igniting again.
- Use pressurized water, foam, or multi-purpose (ABC rated) dry chemical fire extinguishers.
- Do not use carbon dioxide or standard (BC rated) dry chemical fire extinguishers.

Class B fire - requires combustible fluids and gases like gasoline, paint thinner, kitchen grease, propane, and kerosene.

Prevention
- Do not refuel machinery in an enclosed area that is lacking outside flow of oxygen (e.g., open window) or near anything that is burning.
- Avoid adding gas to any equipment that is still hot or has just been turned off.
- Store combustible solutions in tightly sealed, spill-proof bottles.
- Keep combustible solutions away from anything capable of emitting sparks.
- Make sure hazardous materials are inaccessible to children.
How to extinguish
- Cut off the oxygen supply in order to keep dangerous vapors from igniting, and stop a chemical reaction that could create a fire in its tracks.
- Use foam, carbon dioxide, or standard (BC rated) or halon chemical fire extinguishers.

Class C fire - requires electrical wiring or equipment such as appliances, computer, switches, panel boxes, and power tools.

Prevention
- Keep an eye out for wires that have worn out insulation, and replace them.
- Keep motors free of dust and debris to avoid overheating.
- Verify that all utility lamps in use are covered by a guard; heat produced by an exposed light bulb can set normal combustibles on fire.
- Inspect any electrical equipment that is giving off an odd odor because a fire may be smoldering.
- Do not overwork outlets.
How to extinguish
- Shut off the energy source by unplugging or disconnecting the burning equipment.
- Use carbon dioxide or standard (BC rated) dry chemical, multi-purpose (ABC rated) dry chemical, or halon fire extinguishers.
- Do not use water on any equipment still connected to its energy source.

Class D fire - involves exotic metals like magnesium, sodium, titanium, and various organometallic compounds such as alkyllithium. These materials can be rather unpredictable when mixed with water or other chemicals, so they should be dealt with cautiously.

Prevention
- Smothering the burning object with sand may prevent sparks and heat from escaping and causing a chemical reaction.
- For precautionary reasons, purchase Class D extinguishing agents if you intend to use any of the materials listed.
- If it comes in contact with air, white phosphorous will explode or burn. This chemical should only be stored in an airtight container with a special solution that keeps it from reacting with the air.
How to extinguish
- Class D fires can be put out with dry powder extinguishing agents specifically designed for the particular chemical involved. Typically, these agents lower the temperature below the ignition point by absorbing the heat.
- If water is used to extinguish a Class D fire, prepare yourself for a destructive reaction.

Any given fire has the capability of being a combination of more than one type of fire. For example, a fire with burning paper and kitchen grease is considered a Class AB fire.