Fire Fighting - Science of Extinguishment

Science of Extinguishment

See also: Fire Chemistry and Physical properties of wildfires

Fire elements

There are four elements needed to start and sustain a fire and/or flame. These elements are classified in the “fire tetrahedron” and are:

1. Reducing agent (fuel)
2. Heat
3. Self-sustained chemical chain reaction
4. Oxidizing agent (oxygen)

The reducing agent, or fuel, is the substance or material that is being oxidized or burned in the combustion process. The most common fuels contain carbon along with combinations of hydrogen and oxygen. Heat is the energy component of the fire tetrahedron. When heat comes into contact with a fuel, it provides the energy necessary for ignition, causes the continuous production and ignition of fuel vapors or gases so that the combustion reaction can continue, and causes the vaporization of solid and liquid fuels. The self-sustained chemical chain reaction is a complex reaction that requires a fuel, an oxidizer, and heat energy to come together in a very specific way. A chain reaction is a series of reactions that occur in sequence with the results of each individual reaction being added to the rest. This happens in the science of fire, but is self-sustaining in that it continues without interruption. An oxidizing agent is a material or substance that when the proper conditions exist will release gases, including oxygen. This is crucial to the sustainment of a flame or fire.

A fire can be extinguished by taking away any of the four components of the tetrahedron. One method to extinguish a fire is to use water. The first way that water extinguishes a fire is by cooling, which removes heat from the fire. This is possible through water’s ability to absorb massive amounts of heat by converting water to water vapor. Without heat, the fuel cannot keep the oxidizer from reducing the fuel to sustain the fire. The second way water extinguishes a fire is by smothering the fire. When water is heated to its boiling point, it converts to water vapor. When this conversion takes place, it dilutes the oxygen in the air with water vapor, thus removing one of the elements that the fire requires to burn. This can also be done with foam.

Another way to extinguish a fire is fuel removal. This can be accomplished by stopping the flow of liquid or gaseous fuel or by removing solid fuel in the path of a fire. Another way to accomplish this is to allow the fire to burn until all the fuel is consumed, at which point the fire will self-extinguish.

One final extinguishing method is chemical flame inhibition. This can be accomplished through dry chemical and halogenated agents. These agents interrupt the chemical chain reaction and stop flaming. This method is effective on gas and liquid fuels because they must flame to burn.