In arson incidents, suspects may employ plastic items such as lighters and containers for accelerants as tools, which are prone to retaining fngerprint evidence. However, the high-temperature environment of a fre scene can cause plastics to undergo a series of changes including softening, deformation, melting, pyrolysis, and combustion, with the composition of fingerprints also being altered. Therefore, studying the evolution of the fingerprint-bearing substrate under high-temperature conditions holds significant importance for fngerprint development. This study focused on PET plastic mineral water bottles and ABS plastic lighter shells as research subjects. Initially, the thermal properties of these two plastic materials were analyzed to set the heating temperature and duration that simulate fre scene conditions. Subsequently, the latent fngerprints on the heated plastics were developed using the fuorescent powder method, and the evolution of the plastic substrate and fngerprint patterns was observed in real-time via a hot-stage microscope. The mechanism of how high temperature affect fngerprint development on the surfaces of thermoplastic plastics was explained in conjunction with the phase behavior of the substrate materials. The results indicate that the effective ness of fngerprint development on thermoplastic surfaces is predominantly infuenced by the intrinsic properties of the substrate. Before the pyrolysis of thermoplastic materials, the fuorescent powder method can effective ly develop fngerprint, but the ridges will be noticeably distorted due to plastic softening, and the subsequent melting process further severely interferes with fngerprint comparison and identification. Specifically, the PET plastic bottle heated at 200 ℃ for 10 to 30 minutes can still exhibit fngerprint patterns, but prolonged heating exacerbates the distortion. When the temperature rises to 250 ℃, the plastic bottle melts completely, rendering latent fngerprints invisible. For the ABS plastic lighter shell, fngerprint ridges can be revealed but are severely distorted at 250 ℃; when the temperature reaches 300 ℃, the lighter shell undergoes severe deformation, and fngerprints cannot be revealed. The results of this study provide invaluable scientific data to support fngerprint development on thermoplastic plastics under high-temperature fre scene conditions.

Physical evidence is the lifeline of investigation, and scientific and effective examination and identification of physical evidence can provide crucial support in reconstructing cases or events. In the context of fire scene evidence, the focus revolves around the nature of the fire and the analysis and determination of the fire's causes. Particularly in the determination of the fire's causes, identifying the ignition source, the fuel, and the conditions that lead to ignition are the key factors in the final analysis of the fire's origin. During the investigation of a complex fire incident in a production workshop, difficulties were encountered in identifying the fuel and the ignition conditions. Through the application of simultaneous thermal analysis techniques to analyze the thermal properties of relevant physical evidence, parameters such as the thermal decomposition initiation temperature were determined. Upon identifying the point of origin, the heat of ignition was determined through the melting point temperature, and the material first ignited was identified through the pyrolysis temperature. Even though the pyrolysis temperature differs from the ignition temperature, the majority of combustion occurs in the gaseous phase, and combustible gas forms the basis of the combustion process. For polymeric materials, the generation of combustible gas must occur through pyrolysis, making pyrolysis a prerequisite for ignition. Only when the combustible material undergoes pyrolysis and produces a sufficient concentration of combustible gas can combustion potentially occur. Materials were collected from the point of origin in this fire investigation, and using thermal analysis techniques, the initial pyrolysis temperature was theoretically used to reasonably infer and identify the material first ignited, offering crucial reference for the analysis and identification of similar fire incidents.

In this paper, the characteristics of corrosion traces on the surface of Q235 low carbon steel after being heated at 400 ℃, 600 ℃, and 800 ℃ for 15 minutes and the subsequent evolution of these corrosion traces at room temperature were investigated. Polyethylene (PE) was used as the smoke source, and a comparative study was conducted using macro and micro observation methods, color difference analysis, and other techniques to compare the non-corrosive smoke with the smoke generated from PE combustion. The results show that as the heating temperature increases, the oxide layer on the surface of the steel plate becomes coarser and the proportion of the oxygen (O) element increases. The presence of PE cembrstion gas has a significant influence on the high temperature corrosion of the steel plate. Following high temperature oxidation, the oxide skin on the non-flue gas exposed steel plate appears to be convex and pleated. As the temperature rises, the oxide skin gradually develops cracks and eventually peels off, displaying colors ranging from white to red and then to yellow. The steel plate surface exposed to PE pyrolysis atmosphere exhibits a dimming of its metallic luster and tends to become dark, green, and blue. This leads to the formation of a relatively dense and smooth oxidation layer compared to the non-cembrstion gas exposed steel plate. At 400 ℃, the surface oxidation is non-uniform, displaying a more complex morphology compared to the non-cembrstion gas exposed steel plate. At 600 ℃, the surface experiences significant discoloration; yet the oxidation is relatively smooth and uniform. At 800 ℃, the heated surface becomes rough, with some areas showing convex oxides, but there is no evident blistering or shedding observed on the entire surface. With the increase of corrosion time at room temperature, the change of corrosion traces of the two steel plates at room temperature is relatively small, especially when exposed to PE smoke, the corrosion rate of steel plates at room temperature is partially inhibited.