Answer

Fire Dynamics Training Manual

Fire dynamics defines the process by which fire begins to the stage in which it spreads as it develops eventually. In addition, fire is an exothermic chemical reaction in which light and heat are produced as the final products.

Combustion Process

Combustion is a chemically occurring process in which oxygen reacts with a certain substance consequently producing heat. In this case, fuel is the substance reacting with oxygen. An oxidizer is the source of oxygen. The combustion process involves a chain reaction also referred to as rapid oxidation in a process that occurs rapidly.  The process starts with the ignition which can be achieved by several devices some of which include the match among others. The existing friction between a match and the ignition surface results in ignition of phosphorus forming at the end of the match stick. The match sparks and flames causing combustion. (Likhanov & Lopatin,2018)

Stages of Fire Evolution

There are currently four stages of fire recognised internationally which are;

• The Incipient Stage

The incipient stage commences when a fuel source, heat and oxygen combine and the resulting chemical reaction produces fire otherwise referred to as ignition. In fire fighting, the ability to recognise a fire at this stage offers the best chance at escaping.

• The Growth Stage

The growth stage identifies the stage in which oxygen acts as the fuel to the fire. This stage is the deadliest to fire fighters

• The Fully Developed Stage

The fully developed stage defines when the growth stage has achieved its peak and almost all flammable materials have been set ablaze. This phase is the hottest amongst the four and the most fatal to any individual within its range.

• The Decay Stage

The decay stage is the longest stage which is marked by decrease in the fuelling substance which is most commonly oxygen thereby leading to the end if the fire.

Classes of fire

There exist six classes of fire labelled by the alphabetical letters. These are Class A, class B, class C, class D, class E and class F fires. Class A fires involve wood, solid materials, textiles or paper. Class B fires involve those of flammable liquids such as fuels. Class C fires involve gases while class D fires involve burning metals, class E are those of burning electrical appliances. Finally, Class F fires involve cooking oils and fats.

Response to Different Classes of Fire Emergencies

During emergency situations, different classes of fires are handled differently. For class A fires, foam, water and dry powder can be used to extinguish this class of fire. Foam, carbon (IV) oxide and dry powder are preferred for use in extinguishing this class of fire. Dry powder is used to tackle and extinguish class C fires while class D fires are extinguished using special types of powders. These powders are of the L2 and M28 types. Class E fires are extinguished using carbon (IV) oxide and dry powder. The final class E is extinguished using a special wet chemical.

Factors Influencing the Spread and behaviour of Fire

Fire behaviour and spread is influenced by topography, the weather and fuels. Weather influences the spread specifically relating to wind and temperature. High temperatures result in dry vegetation and rapid spreading of fires while wind moves the fires and also adds oxygen to the fire which contributes to combustion. In terms of topography, fires burn faster when burning upslope. Fuels include dry vegetation and existing structures. Trees burn for longer periods producing large amounts of heat compared to dry grass that burns for a short time and generates less heat. (Ponomarenko, Loboichenko, Strelets, Gurbanova, Morozov, Kovalov, & Kovalova, 2019)

References

Likhanov, V. A., & Lopatin, O. P. (2018). The study of the process of combustion of the alcohol-fuel emulsions and natural gas in a diesel engine. International Journal of Applied Engineering Research, 13(3), 1703.

Ponomarenko, R., Loboichenko, V., Strelets, V., Gurbanova, M., Morozov, A., Kovalov, P., … & Kovalova, T. (2019). Review of the environmental characteristics of fire extinguishing substances of different composition used for fires extinguishing of various classes.