August EWJ 24 - Flipbook - Page 39
Table 2. Time stability of impurities of cleaning lids.
drying oven at 100 °C for 4 hours. After we achieved
the results, we tried to improve the method with
adding sorbent materials, the conditions of the treatment (temperature, time) were the same. As sorbent
materials, a bag with activated charcoal as well as
polypropylene were used. The reason of it was to reduce the total amount of impurities. The second
cleaning method was based on the use of solvents (the
method was called as “wet method). Methanol was
used as a polar solvent and isooctane was used as a
non-polar solvent. The requirements for these solvents were that they did not react with the paint of the
lids, as this would release undesirable substances that
would further contribute to contamination. For both
“wet methods”, the lids were placed in an ultrasonic
bath for 15 minutes and then were placed into a
drying oven at 80 °C for other 15 minutes. For the
cleaning methods, the time stability was also tested.
Heat cleaning is effective in reducing contamination.
Heat cleaning together with the use of activated
charcoal proved to be the most effective.
The second method of cleaning, the so-called "wet
method", was also tested. The measured values of the
Total Area of impurities for cleaning lids by using
solvents are shown in the table below (see Table 3).
Results
New sample glass containers with the lids were tested
to demonstrate the contamination of sampling containers. The results showed the number of substances.
The substances were represented especially by di- and
trialkylbenzene and alkanes, which are commonly
found in fire samples.
Table 3. Time stability of impurities of cleaning lids by
using solvents.
First, it was important to find out what part of a sampling container was the source of the contamination.
A total area value, representing the sum of all areas of
individual peaks in a chromatogram, were multiplied
by E-9. It was confirmed that the glass was clean and
the contamination was from the lids. These compounds probably had gotten into the lids in the production and compressing of their seals. The results
also showed that each type of a lid has a different level
of the contamination.
The performed GC-MS analyzes showed that glass
containers with TWIST OFF closures contain contaminants that could affect the chromatographic determination of samples from the fire scene. It turned
out that the impurities came from the lids of the sampling containers. Seal impurities were present in all
types of lids tested.
To achieve the second aim (a proposal of a method for
cleaning), a procedure of thermal cleaning of the lids
was proposed. Heat treatment of the lids reduced the
amount of impurities, see Table 1.
Different methods of lid cleaning were tested such as
thermal, using sorbent materials, using solvents and a
combination of thermal cleaning using different sorbent materials. The temporal stability of the cleaned
lids was also described. A heat cleaning procedure together with the use of activated charcoal sorption material was proposed as the best cleaning method.
Table 1. Total area of impurities of untreated and heat
cleaning lids.
References
1.Cafe, T., Sampling debris at the fire scene. https://www.tcforensic.com.au/docs/article2.html, last accessed 2023/08/07.
2.Lentini, J. J.: Scientific Protocols for Fire Investigation, 3rd
ed., Taylor & Francis Ltd, Great Britain (2018).
3.Phillipps, C.C., McFadden, D.A.: Investigating the Fireground, 2nd ed., Fire Engineering Books & Videos, United
States of America (1996).
Subsequently, the time stability of the heat cleaned lids
was tested. Sample containers with lids modified in
this way were analyzed after the first day, after the seventh day and after the thirtieth day. It was found that
over time, the efficiency of cleaning decreased and the
number of impurities started to increase again. For
this reason, the heat cleaning was improved by using
a sorbent material. The results are showed in Table 2.
EXPERT WITNESS JOURNAL
4.Lang, T.: A Study of Contamination in Fire Debries Containers. Canadian Society of Forensic Science Journal 32 (23), 75-83 (1999).
5.Charvátová, V., Roži ka, M.: Nové poznatky pYi odbru
vzorko akceleranto z požáYišt, Požární ochrana 2014 –
Sborník pYednášek, pp. 88-92. VŠB-TUO, Ostrava (2014).
Contact E-mail addresses:
petra.bursikova@hzscr.cz (Petra Bursikova),
milan.ruzicka@hzscr.cz (Milan Roži ka),
ondrej.suchy@hzscr.cz (OndYej Suchy)
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