Unit 4 Essay
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Unit IV Essay
Components Of Fire
The plume of a fire burning in the apartment in the scenario contains three zones. They can be divided into three regions: the persistent flame, where heat is continually produced by flaming combustion (oxidation) reactions; the intermittent flame, where flaming combustion is irregular; and the buoyant plume, where flaming combustion reactions do not occur (Michaletz, 2007). When a fire plume hits a ceiling, it spreads horizontally, radiating thermal energy and accelerating fire growth. The goal of a fire in a structure fire is to consume all available combustibles. This is important because this is the first step
for a fire to start working towards a flashover. (Wasson, 2015) suggests that when the plume continues to build soot on the ceilings and surrounding materials, the temperature in the compartment rises, and without cooling from a fire attack that compartment will work towards flashing.
Process Of Burning
In the early stage of the scenario, where the oil in the pan catches fire, a diffusion flame occurs preheating adjacent combustible surfaces of the cabinets. The diffusion flame is the beginning phase when fuel and oxidants are initially separated allowing combustion to occur as they are mixed. When mixed, the formation of a hot gas layer occurs beneath the ceiling preheating other surfaces in the kitchen. Diffusion flames turn into turbulent flames as the fire grows more than roughly a foot and begin to heat materials around the stove and kitchen cabinet. The turbulent flame continues projecting heat and flaming across the combustible ceiling, possibly leading to the occurrence of flashover. In the scenario, turbulent flames continue out the window spreading to upper floors and even into the attic through the soffit. On the fire ground, turbulent flames are the most common that firefighters encounter because by the time of arrival the fire has had a chance to start the process of spreading radiative heat that eventually raises a compartment to the level of heated needed to flashover. A two-
way flow occurs through the doorway of a fire room. The inflow through the lower portion of the opening is driven by air entrainment into the flames. The mass outflow through the upper portion of the
opening is slightly higher due to the added mass of the combustion products. This is important to know for firefighters for many different reasons. Controlling an opening in a building with help to control the available air that a fire can use for combustion. This is also important because firefighters know where to concentrate water flow to actively cool an atmosphere and hopefully remove the ability for the material in the smoke to flash or rollover. In a fire, when the ceiling jet has reached the walls, and a hot,
smoky gas layer has formed near the ceiling. Continued burning has increased the (top-to-bottom) thickness of the layer until it extends below the top of the door opening; in addition, the hot, smoke-
laden gases are flowing into the next compartment. (Gann, 2014) suggests a neutral plane interface between the hot upper layer and the cool lower layer composes a somewhat wrinkled horizontal plane. In the scenario, when the firefighters open a door into an adjacent and flames erupt immediately, the neutral plane lowers to 4 ft and the firefighters start to get burned at their ears and hands where their ppe is the weakest. A more common case is that of a compartment with an opening, either by design or
due to a window rupture. Knowing where the neutral plane is at when making entry into a fire compartment is essential for knowing the life safety and survivability of the compartment. If the plane is too low, civilians will not be able to survive.
Reference List
Gann, R. (2014). Principles of Fire Behavior and Combustion (4th ed.). Jones & Bartlett Learning. https://online.vitalsource.com/books/9781284081879
Michaletz, Sean & Johnson, Edward. (2007). How forest fires kill trees: A review of the fundamental biophysical processes. Scandinavian Journal of Forest Research - SCAND J FOREST RES. 22. 10.1080/02827580701803544. Wasson, Rachel & Nahid, Mohammad & Lattimer, Brian & Diller, Thomas. (2015). Influence of a Ceiling on Fire Plume Velocity and Temperature. Fire Technology. 52. 10.1007/s10694-015-0529-3.
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