Fire Investigation- Case Study by Joe Zicherman

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Fire Investigation- Case Study
by Joe Zicherman

Fire Investigation case studies help train fire investigators in the art of fire cause analysis. Like any other specialty, there are key factors to look for and a number of possible conclusions based on the evidence presented. This case presents a typical fire situation that could occur in any city or town in America or another industrialized country.

The fire occurred in the kitchen at a restaurant. When the fire department arrived at the scene they could see heavy smoke but no flames. Firefighters were not able to locate the source of the smoke until the fire - emanating from the floor/ceiling which separated the area from a food storage room below - broke through the floor. Both local fire department investigators and a private fire cause and independent fire investigator, hired by the party who ultimately became the plaintiff in the case, investigated the cause of the fire. Both determined that the fire had started in the void space between the basement storeroom ceiling and kitchen floor.

In the process of conducting the investigation, a fluorescent light fixture mounted to the storeroom ceiling was found in the fire debris. Three investigators concluded, separately, by a process of elimination that the fire had started at the fixture location. The investigators are reported to have ruled out associated building wiring as a fire cause to their satisfaction based on what evidence was available. Like most fluorescent fixtures, the damaged but intact fixture which was recovered contained ballast. The ballast in the fixture is a transformer which converts line voltage to higher voltages capable of powering a fluorescent light tube.

The private cause and origin investigator disassembled the fixture and determined its manufacturer. The ballast was determined to be manufactured by Magnetek, an eventual defendant in the case.

Another expert whose qualifications included a Ph.D. in physics and 20 years experience in studying fires and explosions evaluated the same evidence. He observed oxidation patterns on the fixture and discoloration of the ballast's heating coils. These observations indicated that, prior to the structural fire which occurred; the ballast had shorted, causing internal overheating.

Other Issues:

This ballast design in the fluorescent light fixture contained a device called a thermal protector. The thermal protector is a combination temperature sensor and switch with a thermal reset feature. When functioning normally, the thermal protector would de-energize the ballast when it sensed temperatures reaching a dangerous level. This would cause the light to shut off, signaling to building management that something was wrong with the light installation. If temperatures at the thermal protector fall below 111oC [232o F], the thermal protector restores power to the ballast and the light will once again illuminate.

In the fire at issue, examination of the thermal protector in the ballast demonstrated that it continued to function even after the fire had occurred, effectively eliminating a temperature excursion based on a thermal protector malfunction before the fire. The Court of Appeals’ opinion is silent in terms of testimony as to what management or staff knew about the ballast. However, if it had been cycling, that would have been a sign that thermal failure was taking place.

As part of the investigative process, tests were conducted by plaintiff's experts who faulted exemplars of the ballast at issue and observed the results. In this case, the ballast reached temperatures of 340o F cycled off and then cycled on once again once it had cooled. That testing demonstrated that routine operation of the ballast would occur at temperatures in the range of 149oC [300 o F] as it cycled on and off which is below accepted short term wood ignition temperatures but significantly higher than safe wood exposure temperatures in the range of 90oC [XXX o F] as allowed in our building and mechanical codes and common UL and ANSI standards. at . It is especially critical to consider that The Court of Appeals wrote in its opinion that it believed - based on the evidence provided to that court – that wood ignition occured in all cases at temperatures greater than or equal to 204 o C [400o F].

The plaintiff’s expert expressed the opinion that ballast operating temperatures observed as described above - were lower than ignition temperatures normally accepted for wood adjacent to the ballast. However, the same expert testified in deposition and sought to testify in the trial court that the magnitude of this overheating while below commonly accepted temperatures for the ignition of wood, was sufficient to cause the ignition which occurred because the wood had been subjected to these elevated temperatures for extended periods of time. He characterized that exposure as causing what the court – based on the limited information provided to it - misguidedly referred to in its writings as “pyrolysis”. Accordingly, the plaintiff’ s expert provided an opinion that a short circuit in the ballast created moderate but extended overheating which eventually caused ignition. It was this theory that the Federal Appeals Court referred to as a

Author's Biography:

Posted on: December 31,2007

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