Rapid Fire Progression Phenomena Brian J. Rocker Jr. American Military Institute Abstract Fire fighters are killed every year due to lack of knowledge on the job. This paper focuses on numerous studies that have been conducted on the lack of knowledge regarding enclosure fire behavior, to include: backdraft, flameover, and flashover. This paper, based off the National Fire Protection Association, (NFPA), attempts to combine the many definitions and “truths” floating around about these such phenomena, and clearly define them, and explain the process and possible indicators of these very likely events within an enclosure.
With studies performed by scientists, such as (Dunn) and (Quintiere), this paper explains the lack of knowledge and training those within the fire service profession have today. Keywords: backdraft; flameover; flashover Rapid Fire Progression Phenomena Many firefighters are killed in the line of duty everyday due to rapid fire progression phenomena. Statistics show that enclosure fires are the most dangerous to the fire community. A 2001 study proved that four out of every five fire deaths occurred in residential structure fires.
Cote 10-11) This study confirmed the fear that many in the fire profession do not understand thoroughly about the deadly killers: backdraft, flashover, and flameover. This paper discusses the need for achieving a higher knowledge of fire behavior, especially enclosure fire behavior. The purpose of this study is to make everyone aware about the current lack of training and education regarding these rapid fire progression phenomena.
This paper not only provides a basis for each phenomena, making them easier to understand, but to provide solutions for helping fire safety personnel understand all the components involved in a rapid evolving enclosure fire. Backdraft has not been studied as much as the other rapid fire phenomena. A few studies however have been performed to aid in better understanding of the nature behind it. A team from the University of California, Fleischmann and Pagni were among the first to explore the science of backdraft through experimentation. Fleischmann, 1993) They created a small-scale compartment and were able to reproduce the phenomena, and have been one of the only successful studies for almost a decade. They discovered that “If the compartment is closed, the excess pyrolyzates accumulate, ready to burn when a vent is suddenly opened, for example, as may happen when a window breaks due to the fire-induced thermal stress or a firefighter enters the compartment. Upon ventilation, gravity current will carry fresh air into the compartment. This air mixes with the excess pyrolyzates to produce a flammable, premised gas, which can be ignited in many ways. (Fleischmann, 1993) However a better definition by NFPA standards states “A deflagration resulting from the sudden introduction of air into a confined space containing oxygen-deficient products of incomplete combustion. ” (International Fire Service Training Association, 2001) In better terms, limited ventilation within an enclosure fire can produce large amounts of unburnt pyrolysis products. When a rapid gust of oxygen enters the enclosure, it mixes with the unburned pyrolysis products creating combustible gases.
When ignited from an ignition source, a rapid burning begins by shooting out of the entrance from which it originated from, causing a fireball out of the enclosure. A few indicators include a pulsing structure with smoke seeping in and out under pressure, no visible flames in the room, hot doors and windows, whistling sounds around doors, and discolored or cracked window glass. (Quintiere, 1998) Flashover has been the subject of a numerous of studies beginning way back in the 1960s by the British scientist Phillip H. Thomas. Grimwood, 2003) His initial understanding and definition of flashover was inaccurate, however it was the first time thought was given to this fire progression phenomena. There is, at present, a good understanding of the properties and mechanisms that make up flashover due to a lot of research performed by several scientists. NFPA defines flashover as “…a flashover point, at which all combustible surfaces in a room burst into flame. ” and discusses “…the time interval between the ignition of an incendiary bomb and the time when flashover occurred as a valuable criterion in evaluating the relative effectiveness of various incendiary bombs. (Fire Service Training Association, 2001) Basically, when everything in an enclosed compartment heats up and reaches its level of ignition, everything bursts into flames. Eventually all combustible materials in the vicinity will flash into flame as well. In theory, this is the stage where a fire becomes fully developed. Flashover occurs rapidly, taking only a few seconds to spread throughout the whole compartment. Some components controlling flashover include the temperature before the initial fire, the size and shape of the compartment, the fire growth rate, heat release rate, and the location of the fire within the compartment.
The only real visible indicators include rising temperatures, the sounds of explosions, and the breaking of windows and doors. (International Fire Service Training Association, 2001) Some major misconceptions about flashover include the idea that a “full room involvement means flashover occurred. ” Not all rooms that experience full room involvement have gone through the period of flashover. Ventilation may prevent this from occurring, keeping the temperature just below its flashover point.
Flashover and “full room involvement” are not the same concept and should not be taken as such. (Grimwood, 2003) No research or experiments could be located to could specifically identify flameover. However a paper written by a New York fire chief, Dunn, attempts to define flameover as “the rapid spread of flame over the surface of walls and ceiling walls, and ceilings painted or covered with a combustible finish can exhibit flameover” (Dunn, 2002) He incorrectly defines the idea by saying that the ceilings or walls must be of a combustible nature.
NFPA defines flameover better by stating “the condition where unburned fuel (pyrolysate) from the originating fire has accumulated in the ceiling layer to a sufficient concentration (i. e. , at or above the lower flammable limit) that it ignites and burns; can occur without ignition and prior to the ignition of other fuels separate from the origin” (International Fire Service Training Association, 2001) As with flashover, the initial burning cause gases to rise which heat up the rest of the combustibles present in the vicinity. As more gas fills up the room, it collects under the ceiling, spreading laterally forming a layer.
When it reaches its auto ignition temperature, the gases ignite and create a flame front which will move throughout the vicinity. This only occurs if there is oxygen entering the vicinity from a lower area to keep the upper layer in place. Flameover normally precedes flashover, but is not necessary for flashover to occur. Some indicators of flameover possibly occurring include the formation of a thick dark layer on the ceiling, visibility is very dim, and for the fire fighters entering the structure, the heat from the upper layer is generally almost unbearable.
A lot of flameover prevention training occurs within these chambers where an instructor will demonstrate cooling the upper layer with a variety of streams, and the effects of proper ventilation. (Dunn, 2002) The best way to minimize casualties within the fire service due to these rapid fire progression phenomena include the proper passing of knowledge down the chain of command. Several terms have been defined wrong and have been used interchangeable. These terms should be written more universal in their meanings and usage.
Much of the knowledge gained by those within the fire service profession come from independent learning or certification courses. Most of the findings come from periodicals and journals with technical inaccuracies. NFPA 2001 is not very clear in its requirements for the fire fighter nor the establishment for those requirements. There is no detail on what is specifically suppose to be taught, how it should be taught, what certifications the instructor should possess, nor the amount of time that should be allotted to each section.
Throughout the research and studies performed, it was revealed that the knowledge and science regarding these very active rapid fire phenomena are available. These studies have been studied and researched for some time by scientists. All the mechanisms may not be fully understood, but the basic science behind these phenomena and the basic prevention methods fire service personnel use on a daily basis are understood. The biggest problem is the transfer of knowledge between these researchers and scientist to the other professionals within the fire service profession.
References Dunn, Vincent. “Flameover fires, Flashover fires, What is the Difference? ” Fire Command and Control. New York, NY: 1-12. 2002. Fleischmann, C. , Pagni, P. “Exploratory Backdraft Experiments. ” Fire Technology 21. 1993. Grimwood, Paul, “FLASHOVER . a firefighter’s worst nightmare! ,” www. firetactics. com, February, 2003. International Fire Service Training Association. Essentials of Fire Fighting. 4th ed. Oklahoma State University, Oklahoma: IFSTA, 2001. Quintiere, J. Principles of Fire Behavior, Albany N. Y. : Delmar, 1998.
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