Examination of Firearms Review: 2007 to 2010 - Interpol

Although alternative fuels have been a marginal part of fire debris analysis, in the
near future the amount of samples is supposed to increase. An introduction to
different types of biodiesel fuels, their sample preparation and analysis has been
published. 1, 91 In a study of spontaneous ignition of biodiesel samples, it was found
that the autoignition temperature of biodiesel is much lower, being in isothermal
conditions around 100 °C, than in vegetable oil. The inner temperature of the sample
rose rapidly with generation of smoke and the flash point of biodiesel is dependent on
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the concentration of methanol originated from the manufacturing technique.
The following studies about the deposition of vegetable oils and biodiesel samples
need to be noted. When dealing with fire debris samples, extraction of ignitable liquid
residues needs to be carried out first. Fatty acids of vegetable oils are not disturbed if
samples are heated in 65 °C for 16 hours. Solvent extraction is needed to recover
vegetable oils, but fatty acid methyl esters (FAME) are volatile and can be analyzed
by a passive head space. Heavy gasoline distillate chromatogram changes when
FAMEs are present; in such a case the identification of every extraneous peak is
essential in order to detect the presence of biodiesel. Another challenge with
suspected vegetable oil in fire debris are storage conditions of fire debris samples, as
they should be waterless and the samples sealed well to reduce degradation. The
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ageing of such samples, including biodiesel samples, must be studied further.
An analysis method for vegetable oil from fire debris has been developed. Different
derivatization methods were optimized in order to convert fatty acids into esters.
Furthermore three various columns and different GC programs were used. Base
catalysed trans-esterification derivated fatty acids in vegetable oils successfully and a
polar column separated the peaks clearly. The study serves as a starting point for
research in fire debris in respect to vegetable oils. 95 A fast sampling and analysis
method of another kind is solid-phase microextraction (SPME) used with a gas
chromatograph. In this method, thermal desorption of unsaponifiable substances was
carried out first. Then the remaining oil in the fibre was recovered with solvent, further
base-catalysed trans-esterification and injected to GC-MS. The analysis was made
by using two different gas chromatographs with proper columns in the oven. This
method provided more useful information than the reference method. 96
Self heating tendency and thermal stability of vegetable oils have also been studied
with differential scanning calorimetry (DSC). Being a fast and useful technique, it is
possible to use this method when a sample of questioned oil is available from the fire
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scene.
An analytical method of C80 calorimeter was used to identify reasons for
spontaneous combustion of cotton. Calculating the thermal behaviour of cotton and
its self-accelerating decomposition temperature, variation of results with different
parameters demonstrated that water plays a key role in the process. Further
consideration seems to be that microbiological degradation of cotton generates
oxygen and methane which could lead to ignition. 97
Spontaneous combustion of laundry has been unrecognised as a fire hazard. Ignition
of laundry from restaurants or hotels with stains some customary cooking oils has
been investigated as to tendency to ignite cotton material. The tests showed that the
prevalent temperature level together with the oil’s properties influences the auto-
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