Background Interference in Fire Debris Analysis

Abstract

In fire debris analysis, the presence of any volatile compounds in the sample that may interfere with the identification of an ignitable liquid is known as the background. These volatile and semi-volatile background compounds may originate from both burned and unburned materials (substrates) at the fire scene, from fire suppression activities, and even from materials brought to the scene by fire investigators. Background compounds that originate from burned and unburned materials typically arise via three different mechanisms: pyrolysis, combustion, and distillation. The interfering compounds generated from different burned materials, such as wood, plastics, and human remains, and unburned materials, such as building materials, clothing, and decomposing human remains, are discussed. An overview of the chemical reactions that give rise to some of the more commonly encountered substrates of wood and plastic is given. In addition, the background compounds that may be introduced to a fire scene as a result of fire suppression activities (i.e., foams), as well as materials used by investigators to collect samples at a fire scene (i.e., gloves and absorbents), are reviewed. Finally, the importance of generating pyrolysis data from a variety of burned and unburned substrates, and how this data assists in identifying which compounds extracted from a sample of fire debris originated from the substrate and which came from an ignitable liquid, is presented.