Fire/Arson Investigations : Fire/Arson Investigations
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Re: Fire Origin Pattern Persistence
Posted by: dcarpenter (IP Logged)
Date: October 31, 2016 10:59AM
As you are well aware of, there are other other methods to test origin hypotheses outside of pure use of fire patterns. Use of the fundamentals of fire dynamics and the reliable application of the Scientific Method is the overriding methodology.
The problem comes from the difficulty of generalizing the application of fire dynamics to a generalized set of conditions. As previously noted, "time is the yardstick of fire." An investigator can use time lines as a means to test origin hypotheses. There are a whole host of time-dependent fire phenomenon that may be applicable to a specific set of fire circumstances that can help disprove an origin hypothesis.
Again, this work can be characterized by being "necessary, but insufficient" to be able to reliably say that fire patterns are persistent in actual fire incidents. They may persist or they may not persist given sufficient time.The time frames in the testing provide a limitation with respect to the application being substantially similar in any given case.
John's reference to the "z-factor" paper by Carman is an excellent example of how fire dynamics can be used to test origin hypotheses.This phenomenon of the fire source becoming vitiated by being immersed in a layer of products of combustion is usually associated with a fire source low (i.e. on the floor) and the hot layer descending downwards to the floor. This requires an understanding of entrainment into fire and thermal plumes. It is the same phenomenon associated with the development of a ceiling jet immersed into a hot upper layer. Use any zone model and move the elevation of the fire and you will see this effect.
Application of fundamentals to specific sets of circumstances sometimes requires creativity and thinking differently, as shown by Carman as well as in the case in Davies, FL with a fire originating in the Halogen lights mounting close to the ceiling.
Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com
The problem comes from the difficulty of generalizing the application of fire dynamics to a generalized set of conditions. As previously noted, "time is the yardstick of fire." An investigator can use time lines as a means to test origin hypotheses. There are a whole host of time-dependent fire phenomenon that may be applicable to a specific set of fire circumstances that can help disprove an origin hypothesis.
Again, this work can be characterized by being "necessary, but insufficient" to be able to reliably say that fire patterns are persistent in actual fire incidents. They may persist or they may not persist given sufficient time.The time frames in the testing provide a limitation with respect to the application being substantially similar in any given case.
John's reference to the "z-factor" paper by Carman is an excellent example of how fire dynamics can be used to test origin hypotheses.This phenomenon of the fire source becoming vitiated by being immersed in a layer of products of combustion is usually associated with a fire source low (i.e. on the floor) and the hot layer descending downwards to the floor. This requires an understanding of entrainment into fire and thermal plumes. It is the same phenomenon associated with the development of a ceiling jet immersed into a hot upper layer. Use any zone model and move the elevation of the fire and you will see this effect.
Application of fundamentals to specific sets of circumstances sometimes requires creativity and thinking differently, as shown by Carman as well as in the case in Davies, FL with a fire originating in the Halogen lights mounting close to the ceiling.
Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com
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