Study on the methods of visualizing bloodstains after thermal exposure.

To establish the correlation between thermal conditions imposed on bloodstains and visualizing effect of enhancement techniques, infrared photography and four chemical enhancement reagents were used to visualize bloodstains following thermal exposure. A black tile was selected as the substrate to intensify the visualization challenge, with a Cone Calorimeter serving as the standardized heating source to control thermal conditions. Compared with standard photography, infrared photography is proven to be a valuable complement to chemical reagents, showing significant advantages in visualizing bloodstains after thermal exposure. However, it is worth noting that infrared image fell short of standard image when bloodstains displayed raised, embossed morphology or when bloodstains almost disappeared under specific conditions. The enhancement effectiveness was found to be strongly correlated with thermal conditions imposed on bloodstains, and the morphology evolution of bloodstains during heating affected the chemical enhancement effect additionally, especially when the bulge morphology was formed, and it was observed that reagents were more effective after removing the dense shell of the bulge. Among the four selected chemical enhancement reagents, fluorescein performed exceptionally well, maintaining its effectiveness even for bloodstains heated at 641°C for 10 min. TMB demonstrated its visualizing ability for bloodstains heated at 396°C for 5 min and heated at 310°C for 20 min. BLUESTAR® followed afterwards, while luminol performed worst. The correlation between thermal conditions imposed on bloodstains and the corresponding visualizing effectiveness of enhancement techniques provides important references for detecting bloodstains at fire scenes.

Research Progress on Biological Evidence Identification in Fire Scenes.

Biological evidence is relatively common evidence in criminal cases, and it has strong probative power because it carries DNA information for individual identification. At the scene of fire-related cases, the complex thermal environment, the escape of trapped people, the firefighting and rescue operations, and the deliberate destruction of criminal suspects will all affect the biological evidence in the fire scene. Scholars at home and abroad have explored and studied the effectiveness of biological evidence identification in fire scenes, and found that the blood stains, semen stains, bones, etc. are the main biological evidence which can be easily recovered with DNA in fire scenes. In order to analyze the research status and development trend of biological evidence in fire scenes, this paper systematically sorts out the relevant research, mainly including the soot removal technology, appearance method of typical biological evidence, and possibility of identifying other biological evidence. This paper also prospects the next step of research direction, in order to provide reference for the identification of biological evidence and improve the value of biological evidence in fire scenes.

[Research progress on interference in the identification of accelerants in a fire scene].

Fire is one of the most common disasters threatening public safety and social development; arson, a typical violent crime, is a serious threat to people's lives and property. Suspects are likely to use accelerants to commit effective and rapid arson. Therefore, the identification of accelerants is of crucial importance in determining the nature of a fire. Fires are commonly complex and intricate, leading to remarkable interference in accelerant identification. During the development of a fire, thermal environment influences the preformed accelerant combustion residues, causing the characteristic components of the accelerant to volatilize/pyrolyze to different degrees, thus interfering with accelerant identification. There are numerous petrochemicals with characteristic components similar to those of accelerants in fire scenes, also contributing to the interference in the determination of the presence of accelerants. After the fire is extinguished, the combustion residues of the accelerant in the fire scene are influenced by the combined effects of heat, light, and pressure in the ambient environment, resulting in the loss of the mass fraction of characteristic components, mainly in the form of volatilization. In particular, with countless microorganisms in the soil, the characteristic components of the present accelerants are degraded, resulting in the reduction or absence of some components, which seriously influences the accuracy of accelerant identification. This study describes the progress of research on the interference in accelerant identification induced by various factors at fire scenes from four aspects: thermal environment, matrix interference, weathering effect, and microbial degradation, with emphasis on the interference from the first aspect. Based on the correlation between the matrix chemical composition/structure and interference degree, new results pertaining to the interference source in accelerant identification are also considered. The shortcomings of current research and the prospects for future research are put forward to provide a reference for accelerant identification at fire scenes. Many studies have been conducted on the above four types of interference in recent years, which provide important reference for accelerant identification regarding the arson caused by ignitable liquids. However, with the application of new materials and techniques, fire scenes have become increasingly complex, which demands higher requirements for accelerant identification in forensic science. Research on thermal environment interference is still in its infancy, and it is of great practical significance to conduct this research on other types of accelerants coupled with other interference factors. In addition, the principle of most of the current research on selecting objects is based on common appearance at fire scenes, rather than the functional group of the chemical structure of the matrix. Systematic and in-depth research on the interference law and mechanism is urgently required, and it is vital to further explore the interference law of the fire background from the perspective of the chemical composition and chemical structure of the substrate. Compared to foreign countries, there is less research on the interference of weathering and microbial effects on ignitable liquid identification in China. Most importantly, there is a lack of unified provisions, such as standard experimental methods to carry out such research, making it urgent to establish relevant standards and specifications. Additionally, while weathering is caused by multiple factors, the existing research on the interference of the weathering effect with ignitable liquid identification focuses merely on volatilization. Therefore, a more accurate experimental design is necessary. Improving the database of interferents under fire conditions, and combining the application of the chemometrics method for the artificial intelligence identification of the combustion residue spectrum, is an effective way to further improve the identification efficiency and accuracy.

The most remarkable interference to gasoline identification from polystyrene-co-butadiene and the corresponding cause.

The identification of ILRs in fire investigations has attracted great attention for decades, and background at fire scenes caused complex interference on ILR identification by contributing characteristic compounds. Aiming at exploring the correlation between the interference extent to gasoline identification and chemical composition/structure, two polystyrene-butadiene rubbers (SBr) with typical styrene contents involving alkylbenzene in molecules were selected particularly. The free burning residues in the presence and absence of gasoline were collected and analyzed via gas chromatography-mass spectrometry. It is striking that SBr with typical styrene content caused the most remarkable interference to gasoline identification as far as reported since it is even impossible to be distinguished from gasoline through chromatography profiles. Additionally, the molecular structure together with the chemical composition influences the interference extent as well. To trace the source of the remarkable interference from SBr, polystyrene, polybutadiene, as well as one polystyrene-butadiene-styrene block copolymer, were picked particularly due to their specific chemical relations. The results of target compounds analysis on the corresponding combustion residues revealed that the remarkable interference of SBrs originated from the combination of 'styrene' and 'butadiene' by contributing different target compounds. The results provide further support for the proposal of the correlation of the interferents chemical compositions with the interference extent. Furthermore, this study provides important references for fire debris analysis by predicting the interference of different substrates on the basis of their chemical composition.

Influence of thermal environment in fire on the identification of gasoline combustion residues.

Recent advances in fire investigation have engendered significant interest in fire debris analysis. Many factors in fire scenes, however, may interfere with the identification of ignitable liquid residues (ILRs). Generally, all ILRs suffer unavoidably from thermal destruction in fires. In contrast to weathering, the thermal effects on ILRs involve evaporation, thermal degradation and other chemical reactions. In order to study the influence of the thermal environment in fire scenes on the stability of target compounds for ILRs identification, gasoline combustion residues were reheated at different temperatures and analyzed by gas chromatography-mass spectrometry (GC-MS) systematically. The results showed that polycyclic aromatic hydrocarbons (PAHs) and indanes were more susceptible to thermal destruction, and could not be detected effectively after heating. On the other hand, alkylbenzenes and condensed ring aromatics were comparatively more stable. When the temperature rose to 600 °C, almost all the target compounds were lost after reheating again for 2 min. The research provides an important reference for gasoline combustion residues identification, and care should be taken on the interpretation of results due to the inevitable thermal damage to ILRs in fires.

[HPLC-FPS establishment of Iris japonica Thunb].

Samples extracted from the root of Iris japonica Thunb were analyzed and the optimal HPLC chromatographic conditions was confirmed. Through analyzing the chromatography, the HPLC-FPS of Iris japonica Thunb was established.