What is Fire

Fire is a chemical reaction that occurs when the chemical structure of a fuel is broken by heat energy, in the presence of oxygen. The decomposition of the fuel by heat releases light and heat. This combustion reaction continues in a chain reaction until one of the components - fuel, heat or oxygen - is no longer sufficient to continue the reaction. By - products of the chemical reaction are smoke /unburnt fuel and carbon/, and new chemical compounds such as carbon dioxide, carbon monoxide, and water. If any of the factors needed to produce fire /fuel, oxygen, heat/ are not in the proper ratio, there will be little or no combustion reaction.

Classification of Fires and Extinguishment Methods

Class “A” fires can involve ordinary combustible materials, such as wood, cloth, paper, rubber and many plastics. Water is used in a cooling effect to reduce the temperature of the burning material below its ignition temperature.

Class “В” fires are fires involving flammable liquids, greases, and gases. The smothering or blanketing effect of oxygen exclusion is most effective. Other extinguishing methods include removal of fuel and temperature reduction.

Class “C” fires are fires involving energized electrical equipment. This fire can sometimes be controlled by a nonconducting extinguishing agent. The safest procedure is always to attempt to deenergize high voltage circuits and treat as a Class “A” or “B” fire depending upon the fuel involved.

Class “D” fires are res involving combustible metals, such as magnesium, titanium, sodium, zirconium, and potassium. The extremely high temperature of some burning metals makes water and other common extinguishing agents ineffective. There is no agent available that will effectively control fires in all combustible metals.

Special extinguishing agents are available for control of fire in each of the metals and are marked specifically for that metal.

Combustion

Fire and combustion are terms that are often used interchangeably. Technically, however, fire is a form of combustion. Fire is a rapid, self-sustaining oxidization process accompanied by the evolution of heat and light of

varying intensities. For many years, the fire triangle (oxygen, fuel, and heat) was used to teach the components of fire. While this simple example is useful, it is not technically correct. For combustion to occur, four components are necessary:

· Oxygen (oxidizing agent)

· Fuel

· Heat

· Self-sustained chemical reaction.

Selection of Extinguishers

The selection of a proper fire extinguisher will depend upon numerous factors including hazards to bе protected, severity of the fire, atmospheric conditions, personnel available, ease of handling extinguishers, and any life hazard or operational concerns.

Portable extinguishers come in many shapes, sizes, and types. While the operating procedures of each type of extinquisher are similar, operators should become familiar with the detailed instructions found on the label of the extinguisher. In an emergency every second is of great importance, therefore everyone should be acquainted with the following general instructions applicable to most portable fire extinguishers.

The general operating instructions follow the letters P-P-P-S. P- Pull the pin at the top of the extinguisher that keeps the handle from being pressed. Break the plastic or thin wire inspection band.

P- Point the nozzle or outlet toward the fire.

P- Press the handle above the carrying handle to discharge the agent inside. The handle can be released to stop the discharge at any time.

S- Sweep the nozzle back and forth at the base of the flames to disperse the extinguishing agent. After the fire is out, probe for remaining smouldering hot spots or possible reflash of flammable liquids. Make sure the fire is out.