Fire/Arson Investigations : Fire/Arson Investigations
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Re: If you were a Judge
Posted by: dcarpenter (IP Logged)
Date: June 01, 2007 06:44AM
Russ,
I am not sure anyone has answered your follow up questions and your post sparked my continued interest. So here is my takeo on this issue.
The scientific method requires both the development and testing of hypotheses. I believe that the investigator did generally apply fundamental knowledge in developing his/her hypothesis, but did he/she test this hypohtesis? You have pointed out that the available scientific literature shows that you need a gravity wave of fresh air to enter the compartment for a backdraft to occur. Based on research conducted in the US and New Zealand, we have a reasonable and general understanding of how backdrafts occur with respect to a vertical opening that allows horizontal flow into the compartment. The mixing of the unburned hydrocarbons through newly introduced air plays a very important role with respect to if a backdraft can occur in an unventilated compartment fire once a new source of ventilation is provided. The hypothesis in this instance introduces a horizontal opening that may allow vertical flows from above and below. This may create a mixing dynamic that may or may not lead to a backdraft. Without further understanding of the mixing process in this specific scenario, it would be difficult to reach a reliable conclusion without further effort. I am not aware of any studies of this configuration in the available scientific litertaure (but I have not also looked hard for any) that would help test this hypothesis. Short of previous work, you are generally left with experiments or modeling to test the hypothesis in this case. Thus, if I were a judge, I would question whether the methodology of the scientific method was followed in this particular case due to a lack of hypothesis testing.
There is also one significant point with respect to the hypothesis that is important from a technical perspective. First, the hypothesis implicitly assumes that the ceiling joists would be the first to fail as opposed to the other structural wood in the attic space. Attic fires tend to vent through the roof since, in general, the thickness of the plywood (assuming a wood structure) is less than the thickness of the dimensional lumber used to construct the roof trusses. In addition, the hypothesis must assume that no insulation is protecting a considerable portion of the surface area of the ceiling joists. Was there insulation in the attic? From my experience, most attic fires vent through the roof first and then spread the fire to lower elevations through drop down if the ceiling collaspes.
Also, you do not have to find the specific hypothesis in the available scientific literature to be able to test the hypothesis. You can apply fundamental knowledge to test a hypohtesis if there is sufficient knowledge that applies.
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
I am not sure anyone has answered your follow up questions and your post sparked my continued interest. So here is my takeo on this issue.
The scientific method requires both the development and testing of hypotheses. I believe that the investigator did generally apply fundamental knowledge in developing his/her hypothesis, but did he/she test this hypohtesis? You have pointed out that the available scientific literature shows that you need a gravity wave of fresh air to enter the compartment for a backdraft to occur. Based on research conducted in the US and New Zealand, we have a reasonable and general understanding of how backdrafts occur with respect to a vertical opening that allows horizontal flow into the compartment. The mixing of the unburned hydrocarbons through newly introduced air plays a very important role with respect to if a backdraft can occur in an unventilated compartment fire once a new source of ventilation is provided. The hypothesis in this instance introduces a horizontal opening that may allow vertical flows from above and below. This may create a mixing dynamic that may or may not lead to a backdraft. Without further understanding of the mixing process in this specific scenario, it would be difficult to reach a reliable conclusion without further effort. I am not aware of any studies of this configuration in the available scientific litertaure (but I have not also looked hard for any) that would help test this hypothesis. Short of previous work, you are generally left with experiments or modeling to test the hypothesis in this case. Thus, if I were a judge, I would question whether the methodology of the scientific method was followed in this particular case due to a lack of hypothesis testing.
There is also one significant point with respect to the hypothesis that is important from a technical perspective. First, the hypothesis implicitly assumes that the ceiling joists would be the first to fail as opposed to the other structural wood in the attic space. Attic fires tend to vent through the roof since, in general, the thickness of the plywood (assuming a wood structure) is less than the thickness of the dimensional lumber used to construct the roof trusses. In addition, the hypothesis must assume that no insulation is protecting a considerable portion of the surface area of the ceiling joists. Was there insulation in the attic? From my experience, most attic fires vent through the roof first and then spread the fire to lower elevations through drop down if the ceiling collaspes.
Also, you do not have to find the specific hypothesis in the available scientific literature to be able to test the hypothesis. You can apply fundamental knowledge to test a hypohtesis if there is sufficient knowledge that applies.
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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