Fire and Explosions

The primary use of forensic science evidence relating to fires is to attempt to identify the source of the fire and to determine whether and what type of accelerant was used to start or spread a fire. Traditionally, most experts who offer fire origin testimony, known as “cause and origin investigators,” are not scientists and have little or no scientific training. They are often local fire marshals who testify primarily based on their technical knowledge and what they learned “on the job” from other similar investigators. Origins of fires are difficult to determine since practitioners in the field recognize that no two fires will burn alike and the evidence has usually been destroyed by the fire itself. Cause determinations, especially for accelerants, proceed on a much stronger scientific footing. The presence of an accelerant is most often detected by its odor, and agencies use dogs or commercial electronic sniffers to detect areas for possible investigation. Gasoline or other petroleum-based products are the dominant form of accelerants used in intentionally set fires. Once an accelerant is detected, fire debris is examined in the laboratory to identify common petroleum-based products using gas chromatography. While the National Academy of Sciences Report was critical of the lack of scientific bases for fire testimony, in the past several years much has been done to attempt to improve and standardize forensic fire investigation, primarily through the development and use of the National Fire Protection Association Guide for Fire and Explosion Investigations.