Investigating Kinetic and Thermodynamic Approaches to Predict Evaporation of Gasoline at Elevated Temperatures for Fire Debris Applications

The determination of an intentional, rather than accidental, fire is often based on the identification of an accelerant, such as an ignitable liquid, in the fire debris. Traditionally, debris samples are analyzed by gas chromatography-mass spectrometry, and the resulting data are compared to a reference collection of ignitable liquids that are representative of different chemical classes. However, the identification of ignitable liquids in fire debris is complicated by the initial complexity of the liquid and the various chemical processes that occur during the fire itself. These processes include liquid evaporation and substrate thermal degradation or pyrolysis. To address chemical changes as a result of evaporation, ignitable liquid reference collections often include chromatograms of evaporated liquids. While the inclusion of evaporated liquids in a reference collection is widely practiced, there is no standardized method by which to perform such evaporations. Moreover, the experimental evaporation of all the liquids in a reference collection to numerous levels is an inefficient use of time, money, and resources.

To overcome the limitations associated with experimental evaporations, we propose the use of mathematical modeling to produce a reference collection of chromatograms of evaporated liquids. In this research, a kinetic-based model and a thermodynamic-based model will be refined and investigated for this purpose. The kinetic model accounts for evaporation rates of compounds in ignitable liquids, whereas the thermodynamic model accounts for vapor pressures. Experimental evaporations of gasoline will be performed at temperatures up to 210 °C, and the accuracy of each model in predicting evaporation will be assessed. Both the kinetic-based and the thermodynamic-based approaches will then be used to generate extensive reference collections containing chromatograms of ignitable liquids representing a range of evaporation levels at different temperatures. A set of simulated fire debris samples will be prepared and compared to the reference collections to demonstrate practical application in the identification of liquids present at any evaporation level in the samples.

The research findings will be disseminated through presentations at regional and national forensic science conferences and publications in peer-reviewed forensic science journals. A webinar will also be developed as a resource to train fire debris analysts in the application of both approaches. All collected data, conference presentations, peer-reviewed publications, and webinar materials will be submitted to NIJ, along with the final research summary. The proposed research and subsequent dissemination will provide forensic analysts with a tool to enhance identification of ignitable liquids in fire debris samples.

This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

CA/NCF