Examination of Firearms Review: 2007 to 2010 - Interpol

etween pairs of diesels whereas principal component analysis (PCA) was applied to
the complete data set to assess variation among the diesel samples. 82-84 The results
of the studies were that one got a strong correlation of PPMC, but had some
retention time troubles, reminding that care must be taken in data interpretation, 83
while the other study succeeded to use PCA in identification natural clusters of
similar diesels and the most discriminatory chemical compounds in the data set
stating that PPMC could be applied in forensic arson investigations. 82 The third
examination included temperature programming of the gas chromatograph in the
PPMC and PCA studies gaining adequate results for use in forensic work. 84
A different approach to statistical methods is covariance mapping by t-tests, in which
power analysis is performed to estimate the number of analyses needed to
discriminate between two samples. As comparative forensic analysis may link an
individual person to a crime in this method, it is crucial to keep the power of the test
high. This means that using a significance level of 5 % the risk of type I error is 5 %.
The error type II occurs when a null hypothesis was accepted incorrectly. In practise,
the significance level of the tests is dependent on the consequences and keeping
them low. 85
Liquid gasoline samples from fire scenes can be subjected to various conditions.
That brings along variation into samples when comparing them to ones purchased
from service stations. Multivariate analysis for fire debris casework has been
developed. Dimensions of gathered GC-MS data was reduced depending on the
method into two or three, four and ten in canonical variate analysis (CVA), orthogonal
canonical variate analysis (OCVA) and PCA, respectively. In this study the
procedures were tested with advance knowledge of the correct assignments. The
method needs to be studied further in order to have an applicable method to fire
debris casework. 86
Sometimes comparison of two different methods and their ability to reveal information
needs to be evaluated. A method for comparing two methods has been published. In
the study the within and between -object variances and covariances were estimated.
Reliability of the two methods was estimated in addition and the parameters were
evaluated with a performance likelihood ratio model. A similar kind of comparison can
be made between different kinds of databases, although care must be taken while
accepting data to the method. 87
3.5 Spontaneous combustion
This subject consists of various substances starting from coal industry, saw dust,
cotton and laundry fires. A major part of recent studies relate to vegetable oils and
biodiesel and their autoignition. Fundamentals of auto-oxidation relate closely to
thermodynamics and the surroundings of the self-heating material. 1, 88 In oil tank
fires oxidation of iron sulphides may lead to tank fires and even explosions. 89 In
another case, the combustible material was Auricularia auricular, dried mushroom. In
2003, a warehouse filled with agaric, cinnamon and aniseed was the starting point of
a severe, fatal fire and the reason is still undetermined. Risks of this kind of materiasl
are underestimated. 90
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