Once the point of origin of a suspicious fire is located, an investigator searches for an "accelerant" which is a flammable liquid that may have been used to increase the speed at which the fire spreads. Most arson fires are set using some type of flammable substance to ensure that the fire spreads quickly and does significant damage. Even with the resulting fire, it is rare that the accelerant is completely consumed and can often be found in porous surfaces such as floorboards or plaster. A highly sensitive portable vapor detector can be used to help identify whether accelerants are present in the fire debris. Samples can be collected and taken to the laboratory for positive identification and analysis.

How does chemistry figure into the investigation process?

The most common accelerants are petroleum products like gasoline and kerosene. These liquids are made up of hundreds of different volatile chemicals and will have a unique chemical signature when analyzed. For instance, a sample of gasoline will have a specific chemical composition because the type and relative number of chemical compounds will be different than another type of liquid like kerosene. Thus, chemical analysis is key to determining what accelerant was used.

How do investigators link what they find to a suspect?

Using chemical analysis, one can determine if a fire was caused by arson. For example, if a fire originated in a bedroom and significant amounts of gasoline were found in the debris located there, this would be a logical clue that the fire may have been set on purpose. Furthermore, the chemical signature of the accelerant can be used to link a possible suspect to the crime. If a person is in possession of a flammable substance that exactly matches that found in the fire debris, this would be good circumstantial evidence to prove that the person may be involved with the fire. However, the police would need to find such a person and locate the necessary evidence to be tested.

Are there problems or limitations with current arson investigation techniques?

At the current time it is nearly impossible to determine the exact brand of flammable accelerant through chemical analysis. This is due to the fluctuations in production by the automobile gasoline suppliers. In addition, the heat of the fire may cause the accelerant residue to be changed somewhat due to evaporation of certain chemicals. Finally, the analysis cannot locate the person that may have set the fire if there are no suspects. Such analysis can link someone to a fire only if a person has been identified and a subsequent search has discovered materials that were used to set the fire. For all these reasons the forensic evidence may not be enough to lead to a conviction.

How is forensic evidence in an arson case viewed by the courts?

There are two types of evidence: direct and circumstantial. Direct evidence is defined as eyewitness testimony. Forensic evidence, such as the chemical analysis of fire debris, is considered circumstantial. Before it can be considered by the court, a scientific procedure must be deemed reproducible and accurate. In the United States, most of the decision- making power regarding whether scientific evidence is admissible is held by the court judge presiding over the case. Most testimony involving this type of forensic evidence is given by expert witnesses, such as scientists working in the laboratory where the analysis was performed. In most cases the forensic evidence can be quite convincing if presented to the jury in a clear manner. Forensic evidence is becoming more important and widespread as the scientific techniques used to analyze samples become better and easier to use.

How are College of Wooster students learning to use forensic science techniques?

Chemistry students at The College of Wooster learn to use the sophisticated instrumentation necessary to carry out arson investigations and other types of forensic chemical analysis. Students in my class actually perform an investigation into a fictitious murder using chemical analysis. This gives them a chance to practice the skills they learned in the classroom and the lab in a "real-life" situation. Students not only learn about what is currently done, but help develop new forensic methods in their research projects. Last summer, for example, a Wooster student investigated a new method of detecting accelerants from fire debris. These findings will be published nationwide.