Identification of hazardous organic substances for fire investigation with portable GC-MS

. First responders employ field-portable gas chromatograph - mass spectrometers (GC-MS) to chemically evaluate compounds that may be drugs, explosives, poisonous industrial chemicals or materials, chemical warfare agents, or other dangerous substances. They can measure a wide range of gases, volatile and semi-volatile liquids, and some solids' vapor emissions. Field-portable instrumentation is easily deployable to identify hazardous substances in-situ during an incident response. Using this strategy, real-time targeted risk mitigation and management decisions may be taken to put stronger safety precautions in place and help resolve incidents. The portable GC-MS was able to provide preliminary analytical data on the volatile organic chemicals present in air samples taken from both active and extinguished fires, according to controlled field testing.


Introduction
Fire investigations play a crucial role in determining the origin, cause, and contributing factors of fires.These events can result in catastrophic consequences, leading to loss of life, property damage, and uncountable environmental hazards.The fire scene suffers many alterations and modifications, and the available evidence is often found burnt, melted, smokestained, and damaged by the thermic effects or by water.The investigator's team must carefully assess the fire scene and make important distinctions between whether a fire was accidental or deliberate (arson fire) [1].
The analysis of combustion products plays an essential role in fire investigations, providing valuable information about the materials involved and potential accelerants.Forensic chemists apply analytical chemistry to extract, isolate, and analyze the target compounds that characterize ignitable liquid residues or fuel nature [2].Understanding how much target analyte must be present in an exhibit for its presence to be conclusively identified (the technique's sensitivity) is one of the many factors to consider when balancing the results of a forensic examination.Forensic fire residue analysis is the examination of evidence material for the presence of ignitable liquids; in this context, sensitivity is of particular importance [3].Because they are composed of volatile organic compounds that can evaporate, ignitable liquids may also be present in an exhibit due to the surrounding environment [3,4,5].Excessive sensitivity in an analysis can cause insignificant quantities of ignitable liquid to be assigned with inappropriately high significance [6].
Gas chromatography-mass spectrometry (GC-MS) has long been a cornerstone technique in analytical chemistry, enabling the identification and quantification of volatile and semivolatile compounds with unparalleled sensitivity and specificity.The use of GC-MS in the field of fire investigation offers multiple benefits.Firstly, it enables rapid and on-site analysis of debris samples, allowing investigators to obtain timely results and make informed decisions during the investigation process.This can be crucial in cases where immediate action is required, such as determining the safety of a fire scene or apprehending potential suspects.Additionally, CG-MS offers high-sensitivity and selectivity, enabling the detection and identification of trace levels of volatile compounds.This is essential when dealing with complex fire debris matrices that may contain a variety of compounds from various origins.The ability of GC-MS to separate and identify these compounds individually enhances the efficiency and reliability of the analysis.
Current techniques are time-consuming and difficult to perform, involving the coordination of in-field sampling and the transfer of these samples back to a central laboratory for analysis.These assessments are also intrinsically time-consuming processes that necessitate stable and controlled conditions governed by external validation standards.Due to these requirements, significant delays elapse between the incident and the eventual reporting of scientific data and recommendations to key stakeholders.The delayed provision of complete scientific advice, which may not be available for hours or days after the initial scene presence, frequently impedes first responders.In this case, detailed and timely scientific advice is not available on the ground at the time of the event.
Person-portable instrumentation introduced into the emergency response mission at the fire scene can give important intelligence on the ground that bridges the gap between the initial discharge of hazardous organic compounds and the reporting of confirmatory data from laboratory operations [7,8,9].
The use of portable GC-MS in fire investigation offers more advantages.On-site analysis can provide valuable information about the progression of the fire and the nature of the materials involved, reducing, at the same time, the risk of sample contamination and preserving the integrity of the evidence.Moreover, they bring the potential to monitor the release of hazardous organic compounds rapidly and continuously into the atmosphere.
In the last years, portable GC-MS are becoming more commonly available, offering different features and capabilities [11,12].
This research aimed to determine whether a portable GC-MS can provide valuable information about volatile organic chemicals from air samples, taken from both active and extinguished fires.The results show that this equipment can help in the timely provision of analytical results, allowing the investigators and researchers to gain access to reliable data needed in the elaboration of technical expertise, and to more effectively manage the risks associated with the release of toxicants into the atmosphere.

Materials and Methods
For the presented study, the performance and capabilities of portable GC-MS equipment were tested using a series of controlled fires where small pieces of textile materials were burned in two different conditions: dry cotton samples and samples of cotton impregnated with gasoline.First, a sample from the ambient air was taken, using conventional air sampling and laboratory analysis procedures.Then, air samples were taken from the smoke plume of each burn, and the results were compared to determine the capability of the portable GC-MS to separate, detect and identify volatile organic compounds generated from a fire, and the capacity to determine the presence of fire accelerators (i.e., gasoline).The same method was applied to the burned material samples after extinguishing them with water.

Materials
Three identical samples of cotton material were used.One sample of dry cotton and one sample of cotton impregnated with gasoline were burnt in an experimental setup described below.Then, the experiment was repeated for an identical sample of cotton impregnated with gasoline, extinguished with water.Each individual sample was burnt separately four times, for a total of twelve controlled fires.

Experimental setup
The controlled burns were set up over a rectangular metal tray.After each burn, the metal tray was replaced to prevent cross-contamination between different burns.The experimental setup is presented in Figure 1.Each piece of textile material was ignited using a lighter and allowed to burn freely until extinguished.For the samples extinguished with water, once the materials were fully involved and burning, samples were collected, and water was poured over the materials until the complete extinguishing of fire.

Sampling method
After each textile sample was involved in active combustion, an air sample was collected from the smoke generated by the fire.The air samples were collected using an SPME (Solid Phase Microextraction) device [13] -see Figure 2.

Portable GC-MS apparatus
Needle trap air samples were analyzed on-site, just after sample collection, using a Perkin Elmer Torion T-9 portable GC-MS.The air sampling device can be inserted directly into the T-9 injection port for on-site analysis.Analytes trapped on the sorbent bed are thermally desorbed in the instrument's injector.The portable GC-MS has capabilities and accessories that are useful for environmental sampling and analysis at fire scenes.
The Torion T-9 Gc-MS features a low thermal mass capillary gas chromatograph (GC) with high-speed temperature programming and a miniaturized toroidal ion trap mass spectrometer (TMS), capable of a nominal unit mass resolution over a mass range of 50 -500 Daltons.With a helium GC carrier gas supply cartridge (2500 psig, 90 cc) on board, the system is self-contained.The equipment has improved onboard library search capabilities, calibration and performance validation processes, the NIOSH database, quantitative results, and two additional sampling attachments [7,8,10].
The method parameters were optimized prior to conducting field analysis using compounds likely to be encountered throughout the investigation.The SPME device was inserted into GC-MS and the needle was exposed to 270 °C for 5 seconds desorption time.Immediately after injection, a 10:1 split ratio was applied for 10 s.A 50 °C initial temperature was held for 10 seconds, then the temperature was increased at a rate of 2 °C/s up to 290 °C and held for 60 seconds to complete the GC temperature program.The analytes were transported to the mass spectrometer after chromatographic separation, using a transfer line temperature of 250 °C.The analytes were then scanned by the mass spectrometer over a mass-to-charge ratio of 43-500 u.It took 190 s for the entire run time.
Data were processed using libraries from the National Institute of Standards and Technology (NIST) database.

Results and discussion
Initially, samples were collected from ambient air to obtain a baseline spectrum.Over this spectrum, spectra were overlapped, obtained from: -Controlled burning of dry textile material; -Controlled burning of textile material, impregnated with gasoline; -Controlled burning of textile material, impregnated with gasoline, extinguished with water.The aim of the research was to provide a quick identification method for the combustion accelerators on-site, using the advanced capabilities offered by modern portable GC-MS equipment.As a secondary objective, the extent to which the combustion accelerants can be identified after firefighting with water by fire crews was investigated.
Figure 3 shows representative chromatograms for each type of burned samples.Despite the complexity of air sampling and the portable type of equipment, the GC-MS was able to identify a large number of peaks within each chromatogram.Many of the identified peaks resulting after analyzing air samples were immediately identifiable using the automated data processing protocol bundled in the equipment.The protocol uses mass spectral matching to an onboard target library and a peak deconvolution software.The product manufacturer has created a mass spectral data library that serves the onboard target list.If a peak could not be found in this library, it was deconvoluted and identified using the NIST mass spectral database [14].In the case of dry cotton sample, the following compounds with significant peaks were identified: 1,2 Ethanediol, Acetic anhydride, 3-Metyl 2-Cyclopentanone, Anhydride methacrylic.When impregnated with gasoline, the following compounds were separated: acetone, ethylbenzene, m&p-Xylene, Cyclohexanone, o-Xylene, 1,3,5 Trimethylbenezene, and 1,2,4 Trimethylbenzene.Figures 4  and 5 present the chromatograms of textile materials burned without and gasoline impregnation.Only peaks that had a consistent library match across all repeated analyzes had their identities revealed.
The results of post-extinguishment sampling and analysis were also analyzed to ascertain whether volatile organic compounds (VOCs) and/or semi-volatile organic compounds (SVOCs) are still being emitted from fire debris.At the same time, the study revealed the fact that, for the studied samples of textile materials, the spectra are almost identical to the one of unextinguished material, so it is possible to detect fire accelerants even after the fire suppression (Figure 3, C) and (D).

Conclusions
The primary aim of person-portable equipment is to provide immediate information to investigators on the release and identification of pollutants at the fire scene, identification of fire accelerants used in case of arson fires, or characterization of the fire debris materials.The results obtained present good resolution, being comparable with the ones obtained using laboratory-based equipment and methods.
The research aimed to develop a method for rapid on-site identification of combustion accelerators.Real-time air sampling and analysis using a portable GC-MS can offer important insights to investigators about organic compounds present in fire debris.Simultaneously, it offers the ability to rapidly detect hazardous volatile compounds released in the atmosphere, posing risks to human health and the environment.
For the air samples prelevated after controlled burning of studied textile materials, the method demonstrated good applicability, the field-based GC-MS method being capable of providing consistent and timely results.Specific compounds were successfully identified for all textile materials analyzed, both self-extinguished and water extinguished.The study revealed the fact that, for the studied samples of textile materials, the spectra are almost identical to the one of the unextinguished material, so it is possible to detect fire accelerants even after the fire suppression.

Fig. 3 .
Fig. 3. Representative chromatograms of air samples obtained using Torion T-9 portable equipment, for the following samples: (A) fresh air, (B) burned dry cotton, (C) burned dry cotton, impregnated with gasoline, (D) burned dry cotton, impregnated with gasoline, after extinguishing with water.

Figure 6
Figure6presents the comparison between the chromatograms of samples from burned textile materials with and without gasoline impregnation.

Fig. 6 .
Fig. 6.The comparison between the chromatograms of samples from burned textile materials, with and without gasoline impregnation.