An Unusual Arson Case by Van Vaerenbergh (Forensic Science Communications, January 2002)
January 2002 - Volume 4 - Number 1
An Unusual Arson Case: Polymer Grains, A Mineral Spirit, Solid Bricks Containing Kerosene, and a Glycolether Used as Fuels
An arson attempt in 1996 in a polyethylene-recycling factory near the city of Ghent, Belgium, failed through the action of the security guard. The guard caught the offenders while they were starting fires at two different locations. The guard extinguished the fires, but the offenders fled. There were no traces of a burglary found inside the factory. An extensive examination involving analysis of the samples and consulting relevant literature revealed that if the fire had not been extinguished, the factory would have been severely damaged.
|Figure 1 Sample incendiary spot Click here to view enlarged image.|
Polyethylene (either high or low density) is a plastic solid of milky transparency. It is prepared by polymerization of liquid ethylene at high temperatures and at either high or low pressure. In the factory, nine incendiary spots were prepared (open bags with grains of polyethylene, different solvents, wood, hard paper plates, and hard paper rolls). One of these spots is represented in Figure 1.
It was necessary to determine the flammability of the incendiaries to identify their components and the consequences if the fires had not been extinguished. Different samples were taken on-site for analysis. Their descriptions are represented in Table 1.
A static headspace gas chromatography-mass spectrometry (GC-MS) analysis was performed for screening and identifying any ignitable liquid (the modified method based on ASTM guideline 1618-97). The chromatographic separations were performed on a Carlo Erba Top 8000 series GC-MS. The chromatographic profiles were compared with standard solutions. The following conditions were observed:
- temperature program 40(1)-8-280°C
- injector split 30ml/min. @ 250°C
- capillary column Rtx-5, 30m*0.32mm*1µm
- carrier gas 50kPa helium
- detector MS EI+ scan 25-325m/z
- detector MS source temperature / oven interface temperature 200°C / 250°C
- headspace (with a gas-tight syringe) 1ml @ 25°C
- 100°C (heating for 1h 30min.)
|Figure 2 Identification of the components of sample 8. Click here to view enlarged image.|
The results of the analyzed samples are represented in Table 2.
The GC-MS analysis of sample 8 (Figure 2) reveals a distribution of two propylene glycol ethyl ether (PGEE) isomers with a ratio of »13:1 and two impurities, propylene glycol monomethyl ether (PGME) and ethanol.
- The white spirit in samples 3A, 4A, 5A, 7A, 9A, and 10A appears similar to 9C, based on the comparison of the chromatogram peaks (height and ratio).
- The kerosene in samples 1C and 2C appears similar, based on the comparison of the chromatogram peaks (height and ratio).
Figure 3 Comparison of the PGEE containing grain samples. Click here to view enlarged image.
- The ratio of the ethoxypropanols and the ratio of the PGEE/PGME were calculated for all the samples with the polyethylene grains and for the PGEE liquid. The ratios are almost the same (D matrix, D evaporation stage); therefore, one can assume that the solvent in the polyethylene grains is identical to the liquid sample 8
(a chromatogram comparison confirms the statement) (Figure 3).
Figure 4 Comparison of the evaporation degrees between samples 5A and 4A. Click here to view enlarged image.
- The white spirit in the samples with polyethylene grains has different evaporation degrees; low evaporation 5A<9A<10A<3A<7A<4A high evaporation (Figure 4).
|Figure 5 Chromatogram of sample 6A. Click here to view enlarged image.|
- Sample 6A probably contains traces of white spirit, but the signals are far below the detection limits for scientific confirmation and significance (Figure 5).
All the samples with the polyethylene grains contained the solvent PGEE. Some of the grains also contained white spirit or kerosene. The liquid in the metal can was PGEE (ASTM class 0.1, oxygenated solvents), an industrial solvent for the production of thinners, lacquers, and dyes; therefore, it is not commonly for sale. The liquid in the plastic can was a white spirit (ASTM class 3, medium petroleum distillates). The green bricks were impregnated with kerosene (ASTM class 4, kerosenes). Table 3 gives a summary of the different fuel characteristics.
The flammability of the PGEE, the white spirit, and the kerosene, with and without the polyethylene grains, was tested in contact with a lighter flame. The liquids and bricks were easily ignited, as was the whole combination. Paper and wood burned easily because of their low autoignition temperatures. Based on the flash point, the white spirit is considered a flammable liquid (< 37.8°C); the kerosene and the PGEE are considered combustible liquids (³ 37.8°C).
Polyethylene (PE) readily ignites but will not sustain combustion. The typical pyrolysis pattern of polyethylene (C 85.7%, H 14.3%) was not encountered because the samples for analysis were not burned (there was no presence of olefins and diolefins with every n-alkane, and there was an absence of the branched alkanes between the n-alkanes).
The mineral spirit- and the kerosene-impregnated bricks can be used to improve the ignition of the PGEE and to improve or accelerate the combustion of the wood, paper, and polyethylene grains. The polyethylene grains will continue burning with great intensity with burning drops, black smoke, and the burned-candle-wax smell. This will result in a violent fire with major damage to materials.