Fire is a necessary evil. Although it has many uses in the human life, it can cause a lot of damage to properties and death. The initiation of a fire is aided by availability of oxygen, combustive matter and heat energy. This notwithstanding, taking effective preventive measures significantly reduce the risk of a fire or minimize its effects.
The first stage of a fire is the ignition stage. According to National Fire Protection Association (NFPA), this stage occurs on the surface of the combustive matter, when oxygen gas combines with heat energy. It is characterized by a small fire which might progress into the next stage or go off by itself. The type of the combustive material and the amount of oxygen determines if the fire will die in this stage. Besides, it would be easier to suppress the fire at this phase.
In case the fire is not put off in the ignition stage, it progresses into the growth stage. This stage is characterized by rising temperature and visible flames. Nonetheless, the flames are only restricted to the area near the starting point of the fire. The progress of the fire in this stage is determined by the area of origin, availability of combustive materials and the height of the ceiling. In this stage, the pyrolysate from the fire and extra combustible end products of partial combustion in the hot gas region ignites. This event is referred as flameover. It is characterized by the flames getting to the ceiling and bending to move horizontally athwart the ceiling. If the energy produced by the fire is more than that being expelled from the room, the temperature rises rapidly leading to a flashover (NFPA). During this time, any person in the room is likely to be trapped, injured or killed.
The flashover occurs when almost all the combustive materials which are in direct exposure to an enclosed fire, catches fire almost concurrently. The flashover transits the fire into the fully developed stage. In this phase, the fire spreads to all combustive surfaces and starts to move out through the openings. This is the hottest stage of the fire and there is little chance of surviving in the fire (Lentini, 2012).
After all the combustive materials are exhausted or there is a significant decrease in oxygen the fire goes off. This is the most extended and the final stage of the fire and it is called the decay stage. Failure to take the necessary precautions during this stage can result into two common dangers. Firstly, if combustive materials which do not produce flame exist and are not fully extinguished, they can initiate another fire. Secondly, a backdraft is prone to arise during this stage. This is an event in which there is rapid re-introduction of oxygen in a fire which has already used up all the available oxygen, resulting into a sudden explosion. These explosions are a great danger to the fire fighters. A backdraft could occur after opening a door or a window to an enclosed room (De Haan and Icove, 2011).
The occurrence of a fire can be prevented by installing smoke sensors in buildings. If the fire has already started, the easiest and safest stage to extinguish it is the ignition stage. Unfortunately, if the fire is not noticed, it is likely to advance to the growth stage. When the fire has already entered the growth stage, the best way to control it is by preventing a flameover. A flameover can be controlled by appropriate ventilation. Horizontal or vertical ventilation allows the superhot air and pyrolysate from the fire to escape from the room. Consequently, the heated ceiling layer is reduced and flameover does not occur (Lentini, 2012).
De Haan and Icove (2011) found that, the absence of a flameover prevents the attainment of the threshold temperature for a flashover to occur. As a result, preventing a flameover leads to the prevention of a flashover. Additionally, a flashover can be prevented by applying efforts to stop the fire. This interrupts the heat flow, compelling the heat to spread out and thus reducing the temperatures. Moreover, a flashover can be delayed by cooling the environment in the room using water.
In the event where the fire had already reached the decay phase, it is important to prevent a backdraft. This is done by cautiously applying vertical airing without opening the doors and windows. Besides, cellar nozzle could be used to apply a fire stream to the fire area, while still preventing the supply of fresh air. (Guo and Bailey, 2011).
Evidently, essential measures ought to be put in place to prevent the occurrence of a fire. Nevertheless if the fire has already started, efforts must be made in order to prevent the fire from moving into the next stage and to end it eventually. This should be done with caution in order to prevent loss of life.
Guo, S., & Bailey, C. G. (2011). Experimental behaviour of composite slabs during the heating and cooling fire stages. Engineering structures, 33(2), 563-571
De Haan, J. D., & Icove, D. J. (2011). Kirk’s fire investigation. Pearson Higher Ed.
NATIONAL FIRE PROTECTION ASSOCIATION.
Lentini, J. J. (2012). Scientific protocols for fire investigation. CRC press.