Fire debris (Forensic Science)
Enormous amounts of debris are typically found at fire scenes. In an intense fire, the bulk of a structure can be reduced to soot and ashes. Sifting through such debris is a daunting task for fire investigators, but the work is worth the effort because the results of fire debris analysis often play a critical role in determining the cause and origin of a fire.
(The entire section is 65 words.)
At the Fire Scene (Forensic Science)
One of the primary goals of a fire investigation is to identify exactly how the fire started. In many cases, fires are accidental, caused by electrical problems, gas leaks, or even lightning damage. In other cases, however, fires are set intentionally by people with malicious intent. Often the presence of an accelerant (a substance used intentionally to increase the rate and spread of a fire) indicates that a fire was purposely set. Accelerant residue is most likely to be found in the area where the fire started, or the origin.
A visual examination of the fire debris is typically the first step the investigator takes. By assessing the direction and intensity of the burn patterns, the investigator can identify the fire’s origin. A classic V-shaped pattern is often seen, as fires tend to burn in a tight area at the base and then spread as they move upward or away from the source. The V points back to the source of ignition, potentially an accelerant pool. Another typical burn pattern is known as a “trailer” or pour pattern. Arsonists often pour accelerant in a constant stream from room to room in an attempt to guarantee that the fire will spread throughout the entire structure.
Visual examinations of fire debris, however, are subjective in nature, as they rely primarily on the experience of individual fire investigators. Also, the damage may be too extreme for an investigator to identify burn patterns, or the...
(The entire section is 367 words.)
Evidence Collection (Forensic Science)
After the origin of a fire has been determined, investigators can begin to collect evidence to be taken to the forensics laboratory for further analysis. Debris is typically collected from several locations within the fire scene using everyday garden tools. If an area of heavy accelerant use has been identified, multiple types of debris from that area are collected. Most likely to contain traces of accelerant are porous surfaces, because accelerants can soak into them and be protected from the heat of the fire.
Different types of debris should be collected separately, even if they are from the same area. If several points of origin or areas of accelerant use are identified, representative debris samples should be collected from each area. In addition to debris from the areas suspected to contain accelerant residue, similar samples of debris that are not suspected to contain accelerant residue should be taken. These control samples are necessary to prove that any accelerant residue detected is not an inherent component in the debris material itself.
Fire debris evidence should be collected and stored in airtight containers. The majority of accelerants that may be present contain volatile components that may be lost in an unsealed environment. The preferred collection receptacle is an unused metal paint can with a friction lid. Glass jars are also acceptable, but only if they have airtight lids. Plastic containers...
(The entire section is 307 words.)
Laboratory Analysis (Forensic Science)
In the laboratory, the samples are subjected to the standard procedures in place for fire debris analysis. Conventional techniques are used to extract residual accelerants from the debris. The choice of extraction procedure depends on the type of debris and on the potential accelerant used. Gas chromatography coupled with mass spectrometry (GC-MS) is the standard analytical technique used for fire debris. The pattern of peaks present in the chromatogram and the chemical information available from the mass spectrum will help investigators to determine whether an accelerant, or any other significant component, is present in the fire debris.
(The entire section is 97 words.)
Further Reading (Forensic Science)
Almirall, José R., and Kenneth G. Furton, eds. Analysis and Interpretation of Fire Scene Evidence. Boca Raton, Fla.: CRC Press, 2004. Provides information about fire scene investigation and the chemical analysis of fire debris.
DeHaan, John D. Kirk’s Fire Investigation. 6th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2007. Covers the physical nature and chemistry of fire and also discusses the various types of fires.
Nic DAÉid, Niamh, ed. Fire Investigation. Boca Raton, Fla.: CRC Press, 2004. Compilation of material on the basics of fire investigation includes discussion of laboratory reconstruction and analytical techniques.
Redsicker, David R., and John J. O’Connor. Practical Fire and Arson Investigation. 2d ed. Boca Raton, Fla.: CRC Press, 1997. Details the various undertakings of fire investigators, from scene investigation to courtroom testimony.
Saferstein, Richard. Criminalistics: An Introduction to forensic Science. 9th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2007. Textbook discusses all subdisciplines within forensic science, including fire investigation.
(The entire section is 158 words.)
Fire Debris (World of Forensic Science)
Fire debris is a general term used to define the debris from a fire that is collected as evidence for laboratory examination. When a fire investigator suspects that a fire might have been deliberately set using accelerants such as ignitable liquids, it is possible to collect and analyze fire debris to see if such products are present.
When a person pours an ignitable liquid onto a substrate such as carpet, furniture, or clothing, that liquid gets adsorbed inside the substrate. When the liquid is set on fire, only the surface of the liquid burns and part of it is protected deep inside the substrate. If the fire department puts out the fire early enough, there are traces of this liquid left where the liquid was poured inside the burned debris. The fire investigator who collects the debris then sends it to the laboratory for analysis. The debris needs to be packaged in special containers that are sealed to prevent vapors of flammable or combustible liquids from escaping.
The forensic laboratory analyzes the debris using chemical techniques. First, the residues of the liquid are extracted from the debris, so they can be analyzed without the debris. For this step, different procedures can be used, but usually the sample is heated and the vapors are trapped onto a charcoal strip. This charcoal strip would then contain the residues of ignitable liquid. These residues are separated from the charcoal using a solvent. Once in the solvent, it is possible to analyze the residues with a gas chromatograph or gas chromatographass spectrometer.
Once the analysis is done, it is important to interpret the results carefully. Modern furniture and clothing are composed of polymers that are based from petroleum products, the same petroleum products that are used to manufacture most of the flammable and combustible liquids such as gasoline, diesel fuel, charcoal starter fluid, and paint thinner. Thus, it is very important for the forensic scientist to be able to distinguish the presence of ignitable liquid from the chemicals that are produced by modern substrates. Only the proper collection, examination, analysis, and interpretation of the fire debris sample allow the forensic scientist to reach the proper conclusion.
SEE ALSO Arson; Canine substance detection; Chromatography; Fire investigation.