When unwanted fires begin, or desired fires are no longer needed, actions to suppress combustion involve scientific principles outlined simply in the fire triangle or fire tetrahedron. Removal of one component (leg) of the fire triangle or interruption of the chemical chain reaction, as depicted in the fire tetrahedron, is necessary to stop the combustion process.
Once you complete the Week 5 readings, write a post to achieve the following:
1. Discuss the methods of extinguishment that can be used to break each section of the fire tetrahedron in a building fire.
2. Also, discuss the methods of extinguishment that can be used to break each section of the fire triangle in a wildland fire.
3. What aspects of this week’s forum did you find most interesting?
#1
We will be discussing various methods of how to extinguish a fire by breaking the fire tetrahedron. In reviewing our lessons and readings in class thus far we know that the fire tetrahedron consists of four components. The components are fuel, oxygen, heat and a chain reaction. In order to extinguish and break the fire tetrahedron we need to break or remove one of the components. The first component to remove is heat in a building fire. The easiest way to remove heat in a building fire is to utilize water or other extinguishing agents like a dry powder chemical. More often then not by applying water in a building fire we will remove the heat and extinguish the fire. A second method of extinguishing fire in a building is to remove the fuel, it is not always practical or safe to remove the fuel from the fire tetrahedron but one example that I can provide would be a fire fueled by a gas source. If we can turn off the gas source by control valve or on/off gauge we eliminate the fuel source and can extinguish the fire. The next component of extinguishing or breaking the fire is to remove the oxygen. A way that I believe firefighters often overlook when applying water to the fire is the steam that is created by the hose pattern, steam can reduce or eliminate the oxygen thus extinguishing the fire. The last way to extinguish a fire in a building is to break the chain reaction of the fire. We can break the chain reaction by utilizing some of the other agents besides water, agents like dry chemical or halon actually tend to smother the fire thus breaking the chain reaction and eliminating the components needed to the fire to grow.
We were also asked to discuss methods of breaking the fire triangle in wildland fires. While obvious placing water on wildland fires to remove heat is often a first line and method utilized but is not always effective depending on variables such as size, complexity and wind speeds etc. There has been a lot of research over the years and methods utilized to smother fires, removing the oxygen and chain reactions of the wildland fires by smothering them with chemical agents dropped from planes and helicopters. Another way of extinguishing wildland fires is by removing fuel and unburnt items from the fires path. This can be accomplished by digging fire breaks with bulldozers, shovels and other machinery by removing un burned trees, shrubs and other fuels to extinguish the fire. A common method also utilized in New Jersey is setting backfires or controlled burns to remove the vegetation in a fires path eliminating any further sources to burn.
The most interesting item in this weeks lessons for me was reading about the mechanical foams. We do not utilize foam often in my department as we usually special call other departments when foam is required. The healthcare system that I work for has recently installed portable foam units, Aqueous Film Forming Foam (AFFF) and Film Forming Fluoroprotein Foam (FFFP) at our helipads. I look forward to learning more about these units and how they function and work.
References:
Rakowska, J., Szczygieł, R., Kwiatkowski, M., Porycka, B., Radwan, K., &
Prochaska, K. (2017). Application Tests of New Wetting Compositions for Wildland Firefighting. Fire Technology, 53(3), 1379–1398. https://doi.org/10.1007/s10694-016-0640-0
#2
First, let us start with the four components of the fire tetrahedron, which are fuel, oxygen, heat, and the chemical chain reaction. You must have oxygen to sustain combustion and enough heat to raise the temperature of the fuel to have a chemical chain reaction.
1. Now we will discuss how to remove a section of the fire tetrahedron in a building fire. Starting with oxygen, if we advance an attack line to the fire room and start spraying water, we will remove the oxygen portion of the fire tetrahedron by converting water to steam, and it will displace the oxygen in the room. Also, when applying water to the burning fuel surface, it will drop the surface temperature, and pyrolysis will not be able to sustain burning. This is removing the heat portion of the fire tetrahedron. Removing the fuel in a burning building does not seem practical in a residential building fire. I could see a fire fueled by a gas line rupture, and turning off the valve would take away the fuel to the fire.
2. I have limited wildland experience, most of what we do on Guam is urban interface. So, all this information is coming from research. To take away the fuel portion of a wildland fire, you can do controlled burns or a burn back. Basically, starting a fire and have it burn back to where the large wildland fire is at. That way, the fire has no more fuel to burn and extinguishing the fire. One way to remove the oxygen portion would be to drop the fire suppression agent from the helicopters or fire tankers. It smothers portions of the fire by forming a barrier from the fuel to oxygen.
3. The part of this forum and research I found most interesting was the wildland operations. I did not realize what all went into fighting a wildland fire. Most of the time, crews are cutting fire lines and cutting brush from homes in the area to try to keep the fire away. That job seems like it would take a lot of energy, and crews are working ten plus hours a day.