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Flashovers Case

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Explosive Emergencies

Firefighting has evolved over the years but one thing remains the same. Flashovers and back drafts still are the most terrifying situation any firefighter will find himself in. Although fire prevention technology has advanced, scientists and firefighters both struggle with the inevitable flashover. Both flashovers and back drafts have proven to be critically dangerous and often deadly in the field. Why are they so deadly, and what causes them to occur? Many steps have been taken to prevent these catastrophes from happening but little has changed. They still remain the most deadly situation a firefighter will face.

After the incipient stage of the blaze, the fire is known as free burning. During this stage the fire may take a turn for the worst. It is at this time the fire may "flash over". The fire releases toxic gases that collect under the ceiling. These gases are combined with "sut" or particles of the burning matter that have not burned completely. It is this sut that gives the smoke its thick black appearance. As the heated toxic gases work their way down they increase the temperature of the surroundings furnishings in the room. This heating of materials without the element of combustion is called pyrolysis Once these items reach a certain temperature they will ignite. This is known as their ignition point. All of these factors must come into play to have a textbook flashover. When the flashover does occur it will be sudden, almost without warning. The products in the room will simultaneously ignite. This ignition will create an explosive effect of the room and everything will be in flames within seconds.

There are very few warning signs of a flashover. The only thing that will happen is the temperature will increase significantly prior to the ignition and you will see signs of rollover. According to rollovers consist of as sporadic flashes of flame mixed with smoke at ceiling level. Rollover is caused by heated combustible gases in smoke, which ignites into flashes of flame when mixed with oxygen in the air. Rollover precedes flashover. Rollover is another warning sign of flashover, which may be seen in the smoke coming out of the tops of doorways or window openings of burning rooms before flashover occurs. When searching for the location of a fire and there is no discernible heat in the smoke or signs of rollover, firefighters may enter and proceed for some distance into a fire area. However, If one of these warning signs is discovered and a flashover danger exists, defensive search procedures must be used by firefighters. Standard tactics and procedures must be curtailed and defensive search and rescue procedures substituted when there is a danger of flashover( Fires are always hot but firefighters use the word "unbearable" to describe the pre-curser to the flashover. Firefighters have under six seconds to retreat out the nearest door before sure death will overtake them.

There are several ways to avoid the devastating flashover. With proper equipment you can choose to either ventilate the smoke, cool the smoke, or suppress the fire. Upon arriving on a scene, truck companies head for the roof to cut vents to let the toxic smoke out. This smoke will bellow out of the cut holes. With all this hot fuel out of the building it gives the engine company a much better perspective on what is going on inside of the building. This immediate ventilation is crucial in fighting a fire. Firefighters also spray their hose up at the roof when entering a building. This lets the water hit the hottest spot and evaporate allowing it to bring down the temperature in the room. By doing this you also dilute the smoke and break up the combustible products in it. There is, however, a specific way to do this. One must know how to properly maneuver a hose stream or else he will put his entire company in jeopardy.

Along with flashovers is something called smoke ignition. This is a phenomena in which the smoke itself ignites not the combustible materials in the room. Smoke ignition is caused by high levels of left over products of combustion. The Smoke itself has enough particles in it to combust. Although it may not sustain combustion it will definitely ignite. With the changing times, may materials are now a composite with some type of plastic. This lightweight material will burn hot and produce a lot of smoke. With this smoke is "Soot". The soot is the particles that have not broken down completely during the combustion process. Most firefighters refer to this smoke as "dirty smoke". This is because the combustion taking place isn't burning all the materials it is capable of. This residue is taken up into the air by convection



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