Identification of ignitable liquids in fire debris analysis using pattern recognition is an important step in determining the nature of a suspicious fire. Complex mixtures that make up ignitable liquids are susceptible to microbial degradation when fire debris evidence is presented in the form of soil. Microbial degradation results in a selective metabolism of certain classes of compounds required for identification of an ignitable liquid. Various ignitable liquids that may be used to initiate or propagate a fire contain different classes of organic compounds. These include normal alkanes, branched alkanes, cycloalkanes, aromatics, terpenes, and others. In this work, microbial degradation of nine ignitable liquids in soil was evaluated over a period of twenty-six days. The degradation of aromatic compounds in gasoline was faster with toluene and C2-alkylbenzenes than in C3-alkylbenzenes. However, the overall loss of aromatics made gasoline chromatographically unidentifiable. The complete loss of n-alkanes in medium and petroleum distillates resulted in patterns that resembled naphthenic-paraffinic products. Normal alkanes were more susceptible to microbial degradation than isoalkanes, which was specifically demonstrated in medium and heavy petroleum distillates. In diesel, pristane and phytane remained prominent in comparison to the normally prevalent n-alkanes, which could no longer be detected post-degradation. The degradation of isoalkanes and cycloalkanes was evaluated in a naphthenic-paraffinic product. Isoalkanes were degraded significantly faster than cycloalkanes. The remaining peaks in the naphthenic-paraffinic pattern consisted solely of cycloalkane compounds, and could no longer be classified as a naphthenic-paraffinic product. The terpene compounds in turpentine were also observed to be susceptible to degradation by microorganisms. The loss of !-pinene, limonene, and camphene was significantly noticeable in comparison to other terpene compounds, such as 1,4-cineole. Microbial biodegradation in different soil types was investigated. The difference in soil texture can affect the rate of metabolism of ignitable liquids due to the variance of available oxygen, nutrients and mobility of the microbial population. The degradation of isoalkanes, cycloalkanes, aromatics and heavier normal alkanes was faster in clay, whereas normal alkanes of lower molecular weight were degraded more readily in sand. There has been no explanation of this occurrence within the scientific literature, however it could be hypothesized that the difference in microbial flora and water saturation levels could affect the selective degradation between the two soil types. Fire debris evidence is often stored for long periods of time before analysis due to case backlogs. The storage condition of arson-related soil samples is a sensitive subject. If evidence, containing soil, is stored at room temperature, petroleum compounds in any ignitable liquid residues that are present will be degraded within a week. Therefore, it is important to freeze or refrigerate soil samples. The storage of both refrigerated and frozen soil samples containing gasoline were evaluated over six months. Less than 6% of the aromatic compounds distinctive of gasoline remained when stored at 5 °C, while minimal change was observed in the same compounds when stored at -15 °C. Microbial degradation of petroleum-based ignitable liquids is advantageous from the environmental perspective. However, within the forensic community the effect of microbial action could lead to misclassification or inability to identify the presence of an ignitable liquid in fire debris evidence.

Fire incidents are a major contributor to the number of deaths and property losses within the United States each year. Fire investigations determine the cause of the fire resulting in an assignment of responsibility. Current methods of fire debris analysis are reviewed including the preservation, extraction, detection and characterization of ignitable liquids from fire debris. Leak rates were calculated for the three most common types of fire debris evidence containers. The consequences of leaking containers on the recovery and characterization of ignitable liquids were demonstrated. The interactions of hydrocarbons with activated carbon during the extraction of ignitable liquids from the fire debris were studied. An estimation of available adsorption sites on the activated carbon surface area was calculated based on the number of moles of each hydrocarbon onto the activated carbon. Upon saturation of the surface area, hydrocarbons with weaker interactions with the activated carbon were displaced by more strongly interacting hydrocarbons thus resulting in distortion of the chromatographic profiles used in the interpretation of the GC/MS data. The incorporation of an additional sub-sampling step in the separation of ignitable liquids by passive headspace sampling reduces the concentration of ignitable liquid accessible for adsorption on the activated carbon thus avoiding saturation of the activated carbon. A statistical method of covariance mapping with a coincident measurement to compare GC/MS data sets of two ignitable liquids was able to distinguish ignitable liquids of different classes, sub-classes and states of evaporation. In addition, the method was able to distinguish 10 gasoline samples as having originated from different sources with a known statistical certainty. In a blind test, an unknown gasoline sample was correctly identified from the set of 10 gasoline samples without making a Type II error.

The fire debris analyst is often faced with the complex problem of identifying ignitable liquid residues in the presence of products produced from pyrolysis and incomplete combustion of common building and furnishing materials. The purpose of this research is to investigate a modified destructive distillation methodology provided by the Florida Bureau of Forensic Fire and Explosive Analysis to produce interfering product chromatographic patterns similar to those observed in fire debris case work. The volatile products generated during heating of substrate materials are extracted from the fire debris by passive headspace adsorption and subsequently analyzed by GC-MS. Low density polyethylene (LDPE) is utilized to optimize the modified destructive distillation method to produce the interfering products commonly seen in fire debris. The substrates examined in this research include flooring and construction materials along with a variety of materials commonly analyzed by fire debris analysts. These substrates are also burned in the presence of a variety of ignitable liquids. Comparisons of ignitable liquids, pyrolysis products, and products from pyrolysis in the presence of an ignitable liquid are performed by comparing the summed ion spectra from the GC-MS data. Pearson correlation was used to determine if substrates could be discriminated from one another. A pyrolysis products database and GC-MS database software based on comparison of summed ion spectra are shown to be useful tools for the evaluation of fire debris.

The detection and identification of the oxygenated class of ignitable liquids is a complex issue for the fire debris analyst. The oxygenated compounds are difficult to recover using traditional analytical techniques since their chemical characteristics are vastly different from those of the petroleum products that compose the majority of the ignitable liquid classes. Previous research has demonstrated that the use of zeolite 13X as an adsorbent in heated passive headspace concentration provides increased recovery of oxygenated compounds in comparison to the conventional activated charcoal adsorbent. This hypothesis was further tested in this work using more realistic casework scenarios. Various carpet, carpet padding and wood types were utilized in a number of burn conditions in order to determine if any substrate interferences were present; as well as to monitor the recovery of oxygenated compounds from these substrates using the proposed zeolite extraction method. The substrates explored did not contribute significant background interference to complicate the identification of the oxygenated compounds. In addition, small volumes of the oxygenated ignitable liquids were easily recovered and identified from all burn states using the zeolite method. A dual-mode extraction with both zeolites and activated charcoal strips as adsorbents was utilized with mixtures of oxygenated compounds and petroleum products to determine if a variety of ignitable liquid classes could be detected and identified in the presence of a variety of substrate matrices within a single extraction protocol. The dual-mode extraction showed that both the oxygenated compounds and petroleum products could be detected and identified using a single extraction protocol in the presence of various substrate matrices. Lastly, an experiment was devised to compare the recovery of the oxygenated compounds using various total available surface areas of both zeolites and activated charcoal strips in order to determine which adsorbent exhibits a greater recovery when all other experimental conditions remain constant. When the surface areas were equalized between the zeolites and activated charcoal strips, the activated charcoal exhibited a greater recovery of the oxygenated compounds. However, the cost effectiveness of the zeolites allows for a greater amount of zeolite beads to be used in order to achieve the same recovery as the activated charcoal strips for a much lower price. Therefore, the findings from this work, in combination with previous research, continue to support the use of zeolite 13X as an alternative adsorbent for the recovery of oxygenated ignitable liquids from fire debris evidence.

In fire debris analysis, substrate contribution refers to compounds present within the material collected that can interfere with the instrumental detection of ignitable liquids or contribute petroleum or alcohol-based compounds, which may complicate the interpretation. The concept of substrate contribution was brought to light by "The petroleum-laced background" by Lentini et al. focusing on commercial products (e.g. tennis shoes, magazines, etc.), the publication successfully illustrated that these products can produce chromatograms similar to those generated by the presence of petroleum-based ignitable liquids (ILs). As a result, Lentini et al. demonstrated that fire debris analysts can identify the presence of ignitable liquids without realizing the compounds in question might be the result of the manufacturing processes, and are inherent to the substrate in question. Therefore, the findings may or may not be probative. Gasoline is easily accessible and is frequently used by arsonists. As such, fire debris analysis focuses primarily on petroleum-based compounds. However, oxygenated solvents, which encompass all oxygen-containing compounds as defined by the American Society for Testing and Materials (ASTM) classification scheme, can also be used in an arson event. Despite the potential to be used as ILs, little is known regarding the recovery of these compounds. Previous thesis projects from the Biomedical Forensic Sciences program at Boston University School of Medicine explored and optimized the use of zeolites in recovering low molecular weight oxygenated ignitable liquids. An isothermal gas chromatography/mass spectrometry (GC/MS) method was also developed to detect these oxygenated ILs. The results from these projects show that zeolites have the potential to be used in forensic casework. Inspired by previous publications and thesis research, the goal of this project was to first develop a reference library on substrate contribution from oxygenates (e.g. ethanol, isopropanol and acetone) present in commercial products using the isothermal GC/MS methods. The development of this reference library included a specific interest in wood treatment products, considering wood is one of the most commonly submitted fire debris materials. The second stage involved an attempt at evaluating extraction efficiencies of activated charcoal strip and zeolites. The results of this project suggested that automotive and food products examined contained only acetone and ethanol respectively, while the variety of oxygenates found in household and personal care products indicated further analysis of additional products in these categories would be beneficial. Moreover, the results also reaffirmed zeolites' role in recovering oxygenated ILs in a controlled testing environment using KimWipes as a non-contributing substrate. However, the instrumental method required some modifications, as there was partial separation between ethanol and acetone. The results from applying products onto wooden blocks suggested that activated charcoal strips recovered more oxygenates than zeolites. This unexpected result prompted an investigation into the existing extraction parameters. The investigation suggested that the wooden blocks themselves were responsible for the unexpected recovery results, and future studies would be needed to understand if this recovery was substrate-specific.

Ignitable liquids consist of either a single organic compound or a complex organic mixture. In regards to fire debris analysis, the analyst is responsible for determining if an ignitable liquid residue is present. However, when extracted from soil-containing fire debris evidence, chemical degradation from microorganisms is observed to result in the loss of compounds based on chemical structure. It can also happen when the evidence container is stored at room temperature before analysis. This can present a challenge to the fire debris analyst when identifying and classifying the ignitable liquid residue based on the criteria established by standard test methods. The purpose of this research was to observe the microbial degradation of fourteen compounds, at room temperature over a period of time, for possible by-product formation that could coincide with compounds normally present in an ignitable liquid. Additionally, a quantitative assessment was performed to observe and record the loss rate of compounds in a representative simple mixture. Finally, the loss rate from the simple mixture was compared to commercially available ignitable liquids. Degradation studies were conducted to observe the microbial degradation of a representative compounds (individually and in a simple mixture, both weathered and unweathered) and seven ignitable liquids of different ASTM E1618 classifications. Potting soil was spiked with 20 µL of a liquid/compound and was allowed to stand at room temperature for a period of time. The simple mixture was evaporated to 50% and 90% using a steady nitrogen gas flow to compare the degradation process to the unweathered mixture. All samples were extracted and analyzed using passive-headspace concentration and gas chromatography-mass spectrometry. The formation of by-products was not observed when degrading the compounds from the simple mixture individually as seen in other research. The simple mixture, unweathered and 50% weathered, resulted in rapid degradation of their oxygenated compounds. The straight-chained alkanes and toluene were observed to be more susceptible to microbial attack than the highly-substituted aromatics and the branched and cyclic alkanes. The 90% weathered mixture followed the same degradation trend as the unweathered and 50% weathered samples, although it only contained two compounds. The loss rates/half-lives for each simple mixture sample (unweathered, 50% weathered, and 90% weathered) were determined to be approximately 3.5, 3.5, and 0.84 days. The unweathered and 50% weathered sample half-lives were similar due to containing compounds with similar susceptibility to degradation, while the 90% weathered sample contained one compound that was more highly susceptible to degradation. When comparing the 3.5 day half-life to the seven different ASTM class liquids, the isoparaffinic product and the naphthenic-paraffinic product had similar rates of degradation while aromatic solvent and normal alkane classes had the shortest half-lives. When observing the degradation of the gasoline, medium petroleum distillate and the miscellaneous, the constituent compounds were seen to exhibit a range of degradation rates that corresponded to half-lives less than and greater than 3.5 days.

It is not uncommon for criminals to start a fire at a crime scene to conceal evidence of the initial crime. The rationale for this can be attributed to the belief that a fire will destroy all physical evidence. It has been shown in previous research that physical evidence in the form of ignitable liquid residues, fingerprints and even DNA (deoxyribonucleic acid) evidence can still be recovered from the scene of a fire. However, testing of fire debris evidence for multiple forms of evidence has no universally accepted protocol or order of testing. The purpose of this study is two-fold. DNA recovered from simulated fire debris evidence exposed to various ignitable liquids and burn conditions was compared to determine under what scene conditions it could be feasible to recover DNA evidence and generate usable profiles. Additionally, DNA recovered from samples subjected to different time and temperature conditions of heated passive headspace concentration (HPHC) were compared to determine if it was advisable to perform HPHC in an attempt to recover volatile ignitable liquid evidence prior to testing for DNA. The HPHC overall had no significant effect on the degradation or recovered quantities of DNA, and, under the conditions tested, this would not preclude testing for ignitable liquids prior to testing for DNA. The presence of ignitable liquids did not affect the ability to recover DNA or result in degraded DNA, while burning samples prevented DNA from being recovered in all but a few samples, primarily semen samples.

Current fire debris analysis procedure involves using the chromatographic patterns of total ion chromatograms, extracted ion chromatograms, and target compound analysis to identify an ignitable liquid according to the American Society for Testing and Materials (ASTM) E 1618 standard method. Classifying the ignitable liquid is accomplished by a visual comparison of chromatographic data obtained from any extracted ignitable liquid residue in the debris to the chromatograms of ignitable liquids in a database, i.e. by visual pattern recognition. Pattern recognition proves time consuming and introduces potential for human error. One particularly difficult aspect of fire debris analysis is recognizing an ignitable liquid residue when the intensity of its chromatographic pattern is extremely low or masked by pyrolysis products. In this research, a unique approach to fire debris analysis was applied by utilizing the samples' total ion spectrum (TIS) to identify an ignitable liquid, if present. The TIS, created by summing the intensity of each ion across all elution times in a gas chromatography-mass spectrometry (GC-MS) dataset retains sufficient information content for the identification of complex mixtures . Computer assisted spectral comparison was then performed on the samples' TIS by target factor analysis (TFA). This approach allowed rapid automated searching against a library of ignitable liquid summed ion spectra. Receiver operating characteristic (ROC) curves measured how well TFA identified ignitable liquids in the database that were of the same ASTM classification as the ignitable liquid in fire debris samples, as depicted in their corresponding area under the ROC curve. This study incorporated statistical analysis to aid in classification of an ignitable liquid, therefore alleviating interpretive error inherent in visual pattern recognition. This method could allow an analyst to declare an ignitable liquid present when utilization of visual pattern recognition alone is not sufficient.

L’identification des auteurs d’incendies criminels où un accélérant a été utilisé demeure à ce jour un domaine de recherche en développement. Les traces biologiques reines pour l’identification de personnes comme l’ADN et les traces papillaires sont généralement détruites, donc rarement recherchées. Pourtant, lier l’auteur des faits au lieu de l’incendie est un réel besoin. Ce lien pourrait être établi par l’inférence de source des traces d’accélérant détectées sur les lieux avec une source potentielle souvent amenée par l’enquête comme des objets saisis en possession du suspect (vêtements), un jerrican ou encore des prélèvements effectués sur ses mains. Dès lors, la question qui se pose consiste à déterminer si les traces d’accélérant détectées sur les lieux et les traces détectées sur l’élément de comparaison partagent une source commune. Ainsi, l’inférence de source de l’accélérant constitue une alternative au manque de traces matérielles de sorte à fournir des éléments de preuve à la suite d’un incendie volontaire. En ce sens, cette recherche propose une approche chimiométrique non ciblée pour l’inférence de source de liquides inflammables en science forensique. Cette approche a été appliquée à un échantillonnage conséquent d’essences non altérées et à un échantillonnage réduit d’essences altérées de 0 à 99% par évaporation et par combustion. L’évaluation des résultats a validé l’hypothèse selon laquelle il est possible de lier des échantillons d’essences altérés ou non, par évaporation ou combustion, indépendamment du mode et du degré d’altération. / The identification of arsonists when an accelerant was used is still a challenging and ongoing research area. Golden standards in forensic human identification such as DNA and fingermarks are usually destroyed during the fire, hence not often looked for. It is yet obvious that the need to link the perpetrator to the arson site exists. This link could be made through a source inference process of the traces of an accelerant detected on site. These traces could be compared with a potential source often brought by the police investigation such as seized items in possession of a suspect (clothes), a jerrican or even hand sampling. Thenceforward, the question arising would be to determine if the traces of an accelerant from unknown source share a common source with the seized item. Thus, the source inference of accelerants constitutes an alternative to the lack of material traces in order to provide evidence in arson cases. To tackle this question, the present research proposes an untargeted chemometric approach for the source inference of ignitable liquids in forensic science. This approach was applied to a large dataset of unaltered gasoline samples and to a reduced one of altered samples by evaporation and combustion between 0 and 99%. The evaluation of results shows that it is possible to link gasoline samples altered or not by evaporation and combustion independently of the alteration mode and degree..

Master’s thesis deals with a determination problem of ignitable liquids from fire debris. The aim of this work is to introduce the properties of used fire accelerants and to give an overview and evaluation of the various techniques which can be conducive to the fire investigator. Determination of fire accelerants from fire debris was made by the technique of solid phase microextraction (SPME) with subsequent chemical analysis by GC/MS. Based on the chromatographic results were established the target compounds and reconstructed ion chromatograms which are typical for some kinds of flammable liquids. There were used gasoline, diesel, kerosene and technical gasoline (white spirit) as the fire accelerants. This work also deals with the influence of interfering products in fire debris analysis, including their identification and characterization. Different kinds of substrates were burned, extracted and analyzed in order to identify all the interfering products that they may release.