Fire-fighting must be carried out at close quarters whenever possible to obviate unnecessary water damage and effectively check fire spread. The position of a fire will usually be very obvious but there are times when the seat of the fire is difficult to locate.
There are many indications fire-fighters can follow to locate a fire. The most usual is smoke, which is composed of toxic gasses and the visible products of combustion, mainly carbon particles and water vapour.
The amount of smoke produced by a fire in a building is not necessarily indicative of the size of the fire but depends upon the type of material burning and the air available to the fire.
Generally, a smoky fire indicates the dangerous conditions of a contained fire that is oxygen-starved and is producing more carbon monoxide (CO) than a free burning fire. A free-burning fire will tend to produce less CO and visibility will be better, facilitating efficient fire-fighting.
The emergence of smoke in various parts of the building is no real indication of the fire's position. Air movements and convection can force the smoke to travel considerable distances. Smoke from a fire rises until it meets a horizontal obstruction where it begins to spread sideways at a slower rate. This 'mushrooming' enables smoke to affect remote areas via lift shafts, ventilation ducting, stairwells, roof and ceiling voids.
Flashover
A flashover is a dangerous phenomenon which can occur when a fire is burning in an unventilated space or small compartment. A low intensity, slow spreading fire which needs little water to extinguish it precedes a flashover. Under these conditions carbon dioxide (CO2) and carbon monoxide (CO) are evolved in copious amounts and the oxygen supply to the fire begins to diminish.
Heat, however, preheats the combustible solids in the room. Combustible vapours emanate (pyrolysis) and fill the room. Should O2 enter the room, all the materials ignite spontaneously with a sudden, explosive force known as flashover. The temperature rises by five times its earlier value, with the fire becoming highly intense and fast-spreading.
In an average dwelling, flashover can occur in under 30 minutes, but with a greater fire load this time is drastically reduced.
Preventive measures
To prevent flashover, early ventilation of the fire must be carried out. When searching for the seat of a fire all the senses must be used.
When outside the building
Vision:
Look for smoke emerging from the building and note its colour. This may indicate what is burning. For example: plastics usually emit dense black smoke, but beware of the exceptions - polyurethane foams emit a yellow/brown smoke.
Flickering - this indicates flames but ensure that the flickering is not a reflection from a window or mirror.
Discolouration of window panes and blistering paintwork indicates a high heat level inside. (See flashover)
Smell:
Certain materials have distinctive odours when they are burning and this will help to locate the fire if the contents of the building are known. Materials with distinctive smells include wood, paper, flammable liquids and plastics.
Listen:
Crackling sounds of the fire and sounds of breakage like a shattering window or the exploding of an asbestos cement roof can indicate direction.
When inside the building
Look for:
The direction of smoke movement - smoke will move away from the fire area and if a sprinkler has activated, the smoke layer drops downwards due to the cooling effect.
Blistering of paint or discolouration due to heat. This indicates that a fire is very close.
Smoke in a dark room by using a torch beam to illuminate it.
Feel for:
Hot walls, floors and doors.
An increase in air temperature or radiated heat.
A cool draught of air that may be feeding the fire.
Listen for:
Crackling or breaking sounds.
The sound of running water, which may indicate the location of an operating sprinkler head.
Search in safety
Fire-fighters should always work in pairs as this promotes confidence and ensures that assistance is available should either get into difficulty.
Breathing apparatus should be worn whenever possible to protect the fire-fighters against smoke and toxic products of combustion.
The air is often cooler at ground level and crawling may provide relief from the effects of heat. This action will also frequently facilitate visibility since smoke tends to be denser at roof level.
Whether crawling or walking in dense smoke or in darkness, one hand must be extended with the back of the hand facing forwards, since if the palm were forward and a live electric cable were touched, muscular spasm would contract the hand to grip the cable.
When walking upright, shift the body mass onto the trailing foot with the advancing foot shuffling to feel for obstructions.
A line of retreat should always be secured either by using a guide line or a line of hose. Should the fire-fighters become disorientated, they could easily follow the line to the exit.
Source: Fire Protection Association of Southern Africa
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