Ignitable liquid residue (ILR)
Ignitable liquid residue (ILR) is the evidence left behind at the scene of a fire. ILR represents the portion of an ignitable liquid that did not burn during a fire. ILRs that are typically found in arson investigations are primarily petroleum based, such as gasoline, diesel, and lighter fluid. There are many different types of ignitable liquids that may be encountered in arson investigations; however, gasoline is the most commonly encountered ignitable liquid. ILRs are identified and classified based on their chemical composition, carbon numbers, and boiling point range. The chemical signature of different ILR types can be seen in the 3D-image plots in Figure 1.
What are ILRs used for?
Ignitable liquids have many everyday uses, such as fuel for vehicles or other machinery, cleaning products, painting products, solvents, and many other uses. ILR provides a fingerprint of the ignitable liquid that may have been used to start a fire. This ILR fingerprint is used to determine the presence or absence of an ignitable liquid and can also be used to determine what type of ignitable liquid was used. In certain cases, the ILR fingerprint can be matched to a specific origin, such as a specific gas station.
Where can they be found?
ILRs can be found in a multitude of places. At suspicious fire scenes, fire debris is collected for ILR analysis. Types of fire debris that often contain high amounts of ILR include materials that are highly absorbent, such as carpet, carpet underlay, textiles, wallboard, wood, and soil. Some ILR chemicals can even be formed as by-products of burning materials or are naturally occurring in the environment. It is thus important to know the chemistry of pyrolysis in order to interpret the analytical results and avoid false positives. Since ILRs can be found in a variety of places, from legitimate uses to pyrolysis products, it is important to collect appropriate reference samples for comparison to fire debris samples suspected of containing ILR. The value in collecting reference samples from arson investigations is that it adds another line of evidence to differentiate between ILR and matrix effects when dealing with hundreds, sometimes thousands, of different compounds.
Why are they important?
Most ignitable liquids have legitimate uses and it is up to arson investigators to determine whether or not the presence of an ILR signature is due to legitimate uses, burnt matrix, or because an ignitable liquid was used in the commission of a crime. Detection of ILR in fire debris can enable a number of court proceedings, such as criminal charges or insurance claims.
Chemistry Matters Consulting Services and Expertise
Deliberately caused fires can cause significant damage to property, to the environment, as well as the potential loss of human and animal life. As long as arson continues to be a major crime, suspicious fire scenes will continue to be investigated. For successful prosecutions to occur, the highest level of scientific expertise is required to interpret the evidence. The Chemistry Matters team is well suited to assist in many of these endeavours. We have the experience to aid in the proper collection and legal chain of custody documentation of evidence at fire scenes to meet litigation scrutiny. We have the litigation experience required for expert witness testimony and are actively involved in arson related research by publishing in peer-reviewed journal articles and presenting at scientific conferences.
Arson investigations are not limited to buildings and property – arsonous wildfires account for a large portion of wildfires and bushfires each year. Human-caused wildfires and bushfires represent substantial economic costs and ecological losses across the globe. While some human caused fires may be due to inadvertent activity (e.g. all-terrain vehicles (ATVs)), others are deliberately started. These fires can be investigated as suspected acts of arson where samples are collected and submitted to the laboratory for the analysis and identification of ILR. Suspected arsonous wildfires and bushfires in which the use of an accelerant is suspected are complex investigations due, in part, to the high abundance of natural background chemicals.
Given the complex nature of forest fire debris, wildfire and bushfire samples require advanced analytical techniques that are not included in standard methods. Chemistry Matters is pioneering the application of comprehensive two-dimensional gas chromatography with time of flight mass spectrometry (GCxGC-TOFMS) to wildfire investigations. GCxGC enables superior separation of ILR chemicals from complex co-extracted matrix chemicals in wildfire debris samples and, when combined with the time-of-flight mass spectrometer, also provides a more sensitive detection limit, meaning we can identify more chemicals at lower concentrations than ever before. Burn patterns can vary with the degree of charring, especially when dealing with a complex matrix. GCxGC-TOFMS is able to differentiate ILR at lower concentrations after longer burning times than conventional GC analysis, as shown in Figure 2.
Fate and Transport
The chemical properties of ignitable liquids that make them so attractive to arsonists may also present a series of challenges to sample collection. Ignitable liquids are highly volatile, meaning they evaporate quickly. They are also susceptible to microbial degradation. Proper sample collection and storage techniques are essential to ensuring sample integrity. Chemistry Matters can provide standard operating procedures specific to each arson investigation in order to maintain sample integrity as well as a legal chain of custody.
Chemistry Matters Inc. has provided expert reports and expert witness testimony for criminal and civil arson investigations. The Chemistry Matters team is actively involved in publishing research in peer-reviewed journals that highlight the advantages of using GCxGC-TOFMS compared to conventional GC-MS in litigious investigations. In addition, effective communication of complex scientific findings to non-scientific stakeholders is critical to the success of any legal case. Visual communication is an effective means at describing results to a broad audience. Chemistry Matters use of GCxGC plots and statistical analysis through our partnership with Statvis Analytics Inc provide compelling visuals that can be understood by attorneys, judges, regulators, and the general public.