Progress Toward the Determination of Correct Classification Rates in Fire Debris Analysis,,

Principal components analysis (PCA), linear discriminant analysis (LDA), and quadratic discriminant analysis (QDA) were used to develop a multistep classification procedure for determining the presence of ignitable liquid residue in fire debris and assigning any ignitable liquid residue present into the classes defined under the American Society for Testing and Materials (ASTM) E 1618‐10 standard method. A multistep classification procedure was tested by cross‐validation based on model data sets comprised of the time‐averaged mass spectra (also referred to as total ion spectra) of commercial ignitable liquids and pyrolysis products from common building materials and household furnishings (referred to simply as substrates). Fire debris samples from laboratory‐scale and field test burns were also used to test the model. The optimal model's true‐positive rate was 81.3% for cross‐validation samples and 70.9% for fire debris samples. The false‐positive rate was 9.9% for cross‐validation samples and 8.9% for fire debris samples.     

Differentiation of unevaporated gasoline samples according to their brands, by SPME-GC-MS and multivariate statistical analysis

One of the aims of fire investigations is to identify associations among accelerants according to their source. In this study, 50 gasoline samples--representing five brands--were analyzed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). Chemometric procedures, such as principal component analysis (PCA) and discriminant analysis (DA), were applied to a data matrix obtained by the target compound chromatogram method, to discriminate samples according to their brand. PCA was successful in finding a natural grouping of samples according to their brand, suggesting that aromatic compounds were more useful than aliphatics for the purpose of this study. DA, if applied to aromatic compounds, gave both a classification ability and a prediction ability of 100%. The outstanding results obtained by this work provide the basis of a data matrix that could be used in real cases of arson to link a sample of unevaporated gasoline to its brand or refinery.     

Comparison of new Ampac bags and FireDebrisPAK® bags as packaging for fire debris analysis

Abstract: The FireDebrisPAK^® bags that were produced by Kapak were considered to be one of the best containers for fire debris. Kapak bags were discontinued; however, from July 2010, Ampac is offering a new packaging material. The aim of the presented research was to compare the properties (durability, background interferences, and permeability) of Kapak bags and packaging material offered by Ampac. The analysis was conducted by passive adsorption from the headspace with subsequent thermal desorption and analysis by GC‐MS. The results proved that the properties of the compared materials are similar. Their greatest advantage is that they are impermeable for components of flammable liquids, so there is no danger of losing analytes or cross‐contamination. Their one significant drawback is that they should not be exposed to temperatures above 80°C. At this temperature, they become soft, their inner layer is compromised (becomes sticky), and they emit some volatile organic compounds. Among them, there are compounds that constitute the components of some of flammable liquids.     

Total Ion Spectra versus Segmented Total Ion Spectra as Preprocessing Tools for Gas Chromatography – Mass Spectrometry Data

Alignment of fire debris data from GC‐MS for chemometric analysis is challenged by highly variable, uncontrolled sample and matrix composition. The total ion spectrum (TIS) obviates the need for alignment but loses all separation information. We introduce the segmented total ion spectrum (STIS), which retains the advantages of TIS while retaining some retention information. We compare the performance of STIS with TIS for the classification of casework fire debris samples. TIS and STIS achieve good model prediction accuracies of 96% and 98%, respectively. Baseline removal improved model prediction accuracies for both TIS and STIS to 97% and 99%, respectively. The importance of maintaining some chromatographic information to aid in deciphering the underlying chemistry of the results and reasons for false positive/negative results was also examined.     

Evaluation of Cross‐contamination of Nylon Bags with Heavy‐loaded Gasoline Fire Debris and with Automotive Paint Thinner

Nylon bags are used for packaging fire debris in several countries, particularly in Europe. The possibility of cross‐contamination during transport from the fire scene to the laboratory, in normal casework conditions in the U.K., was studied for two brands of nylon bags, using simulated heavy‐loaded fire debris. Three experiments were carried out with each brand, using as sample a piece of cotton fabric soaked with gasoline. One experiment was carried out using automotive paint thinner (oxygenated solvent). Each sample was sealed in a nylon bag and stored in contact with eight empty bags. The empty bags were analysed at regular intervals for a period of time up to 8 weeks, using SPME and GC/MS. Cross‐contamination was found for components of gasoline (toluene and C₂‐alkylbenzenes) in the two brands of nylon bags used, after 4 days and 2 weeks. Cross‐contamination using automotive topcoat thinner was detected after 2 days.     

Evaluation of Internal Standards for the Analysis of Ignitable Liquids in Fire Debris

Abstract:  An evaluation of eight compounds for use as an internal standard in fire debris analysis was conducted. Tests were conducted on tetrachloroethylene, chlorobenzene, n-octylbenzene, 3-phenyltolune, and deuterated compounds toluene-d8, styrene-d8, naphthalene-d8, and diphenyl-d10 to measure the extraction efficiency of each compound in the presence of an interfering volatile compound (carbon disulfide). Other tests were conducted to evaluate whether or not the presence of an ignitable liquid or pyrolysis/combustion products from fire debris would interfere with the identification of these compounds when used as an internal standard. The results showed that while any of the eight compounds could be used as an internal standard in fire debris analysis, the more volatile compounds (toluene-d8, tetrachloroethylene, chlorobenzene, and styrene-d8) showed better extraction efficiencies at room temperature than when heated to 60°C. Each of the less volatile compounds (naphthalene-d8, diphenyl-d10, n-octylbenzene, and 3-phenyltolune) performed well during extraction at 60°C, while naphthalene-d8 showed better extraction efficiency in the presence of competing volatiles when extracted at room temperature.     

Comparison of the effectiveness of Tenax TA and Carbotrap 300 in concentration of flammable liquids compounds

The aim of research was to compare two adsorbents, Tenax TA and Carbotrap 300, to evaluate their usefulness as passive adsorbents of flammable liquids compounds. It was also to determine whether Carbotrap 300 could be used in a passive adsorption mode, contrary to manufacturer recommendations. To compare the adsorption properties and the thermal desorption efficiency for Tenax TA and Carbotrap, the components of test mixture were adsorbed and then chromatographically analyzed. The analysis was conducted by means of an automated thermal desorber coupled with a gas chromatograph and a mass spectrometer. This research established that although these adsorbents significantly differ from each other in adsorption properties, each of them can be successfully used for passive adsorption of ignitable liquids compounds. Tenax TA turned out to be more effective for the adsorption of nonpolar, high-boiling compounds, whereas Carbotrap is more effective for polar and volatile compounds. The examined adsorbents differ in their susceptibility to thermal desorption. For Carbotrap 300, after the analysis an additional treatment is required to remove the remnants of adsorbed compounds. With Tenax TA, this additional step is not necessary because the thermal desorption is sufficiently effective that this product is immediately ready for re-use.     

Performance Testing of the New AMPAC Fire Debris Bag Against Three Other Commercial Fire Debris Bags(*)

Abstract: Fire debris evidence is collected and stored in a wide range of containers, including various polymer bags. Four different polymer bags have been investigated, including the NYLON, DUO, ALU, and AMPAC bags. The latter is the successor of the Kapak Fire DebrisPAK^?. Microscopy and infrared spectroscopy were used to elucidate the composition of the bags. Gas chromatography/mass spectrometry was used to investigate performance parameters such as background volatiles, leak rate, cross‐contamination, recovery, and sorption. The NYLON bag was susceptible for leakage and cross‐contamination and showed decreased recoveries. The DUO and ALU bags showed some background volatiles, sorption, and poor recoveries. The AMPAC bag performed excellent: low background, no leakage or cross‐contamination, good recoveries, and only traces of sorption. Heat sealing proved to be the best method of closure. Preliminary studies on AMPAC bags showed that polyethylene clamps are easy to use on‐site and preserve ignitable liquids adequately for a limited period of time.