A method for judging close contact with fire source based on slight thermal damage of hair
Observing hair samples by scanning electron microscope, the problem of difficult to identify minor hair thermal damage in the prior art is solved, and the accurate judgment of the suspect's close contact with the fire source is achieved, and the identification ability of criminal investigation technology is improved.
Patent Information
- Application Number
- CN202311854754.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-29
- Publication Date
- 2025-01-10
- Estimated Expiration
- 2043-12-29
AI Technical Summary
The prior art is difficult to effectively identify and identify minor thermal damage traces of hair, especially in the judgment of whether the suspect is in close contact with the fire source. It is difficult for ordinary optical microscopes to observe microscopic damage, and common methods are of little significance to the inspection of minor thermal damage. .
Scanning electron microscopy (SEM) is used to observe hair samples, with a magnification of 500-1000 times, focusing on the epidermal layer of the hair, looking for abnormal surface areas, such as bending of hair shaft, local enlargement of diameter and irregular protrusions, and adjust the magnification to greater than 1000. , observe the cracks, separation and epidermal cracks of the hair scales, and make judgments based on characteristic traces.
Through high-ratio observation and meticulous analysis of SEM, slight thermal damage marks in hair can be accurately identified, which improves the probative and inspection significance of personal identification in fire-related cases, and provides stronger physical evidence support.
Smart Images
Figure CN117805164B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for identifying slight thermal damage to hair, in particular to a method for judging whether a person has come into close contact with a fire source based on slight thermal damage to hair, and belongs to the field of technical identification of physical evidence in fire-related cases. Background Art
[0002] In arson fires, even though the nature of the fire can be determined, it is difficult to identify the suspect and determine whether relevant personnel are present at the scene. Therefore, thermal damage to human hair is very convincing in determining whether a person has been in close contact with the fire source or was present at the fire scene. For example, when an accelerant is used to ignite a fire, it is very likely that traces of thermal damage will form on the suspect's hair on the hands, head, and face. In reality, the hair that is directly exposed to the flame or baked for a few seconds at a very close distance (within 1 cm) has obvious damage (see Wang Ping, Zeng Yuping, Wang Xiaoming, et al. A case of camouflaged corrosive damage detected by hair inspection [J]. Criminal Technology, 2010, 0(1):59 and BOHNERT M. Thermal Trauma [M] / / HOUCK MM. Encyclopedia of Forensic Sciences, Third Edition (Third Edition). Oxford: Elsevier, 2023:743-754). The area outside the flame that is mainly heated by thermal radiation can also cause thermal damage to the hair, but it is relatively mild and difficult to distinguish with the naked eye. The damage to the hair caused by short-term / instantaneous thermal radiation at a temperature lower than the flame temperature (less than 300°C) and difficult to detect with ordinary optical instruments such as magnifying glasses and optical microscopes is called slight thermal damage to the hair.
[0003] The commonly used method at present is to analyze the damage of hair through a magnifying glass or optical microscope. This method is acceptable for observing hair with severe thermal damage, but for microscopic mild thermal damage, when the magnification is increased to 500 times or more, since hair is three-dimensional and has a certain volume, the optical microscopic observation of its surface (cuticle) will be affected by focusing problems, and the magnification of 500 times is not enough to observe the hair surface. In addition, elastic strength testing and sample sectioning (see Xu Wenlong, Zhang Hongmao. The influence of physical and chemical factors on the morphological structure of hair [J]. Journal of Forensic Medicine, 1990 (3): 6-10) will damage the physical evidence, and judging whether the hair has been damaged by heat by color changes is subjective. In addition, the above methods are of little significance for the inspection and identification of hair with mild thermal damage.
[0004] In summary, it is necessary to create an analysis and determination method for slight traces of thermal damage to the hair to support criminal investigators in determining whether a person has been in close contact with a fire source in fire-related cases. Summary of the invention
[0005] In view of the above-mentioned defects of the above-mentioned prior art, the present invention proposes a method for judging whether a person has been in close contact with a fire source based on slight thermal damage to the hair, which uses a scanning electron microscope (SEM) observation method to inspect and identify traces of slight thermal damage to the hair at a microscopic level.
[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:
[0007] A method for judging whether a person is in close contact with a fire source based on slight heat damage to hair comprises the following steps:
[0008] Step 1: Extract hair evidence;
[0009] Step 2: After the hair sample is sprayed with gold, its epidermis is observed by scanning electron microscope (SEM);
[0010] Step 3: The SEM magnification is 500-1000 times, focusing on the epidermis to observe the hair scales distributed on the surface of the hair;
[0011] Step 4: Look for areas of surface abnormalities along the hair shaft that may have caused slight thermal damage, such as bends in the hair shaft and areas where the diameter is locally enlarged;
[0012] Step 5: For the abnormal areas, adjust and increase the magnification of the scanning electron microscope (SEM) to observe the hair cuticle;
[0013] Step 6: Observe and record signs of hair scales cracking, separation, and cracks in the epidermis to determine whether people have been in close contact with fire sources.
[0014] Furthermore, the epidermis observed in step 2 is the stratum corneum of the epidermis.
[0015] Furthermore, in step 4, the surface abnormalities include hair shaft bending, local enlargement of diameter and irregular protruding areas.
[0016] Furthermore, in the step five, the magnification of the scanning electron microscope (SEM) is adjusted and increased to be greater than 1000 times to further analyze the trace characteristics of the details.
[0017] Furthermore, in step 6, the specific judgment method is: focus on checking the area where the hair is curved, the diameter of the hair tip and the shaft is significantly increased and expanded, and check whether there are the following types of slight heat damage marks in this area:
[0018] The first type: multi-layer rupture of the hair scales, manifested as the rupture of the hair cuticle or the complete splitting of the hair cuticle, exposing the hair cortex and the multi-layer structure of the hair cuticle cracking or separation;
[0019] The second type: long cracks on the surface, which are fine cracks with a length of more than 10 microns, a width of less than 1 micron and spanning several hair scales, or cracks with a length of between 5-10 microns, spanning several hair scales and a width of more than 1 micron;
[0020] The third type: fine cracks, which appear as fine cracks on a single hair scale with a length of 5 microns, a width greater than or equal to 1 micron, and a depth of only the thickness of a layer of hair scales;
[0021] If the first type plus the second or third typical slight heat damage signs mentioned above are found in the area at the same time, it is judged that the person has been in close contact with the fire source; if only the second or third typical slight heat damage signs are found, it can be inferred that the suspect may have been in close contact with the fire source; and when the hair is intact and straight, the top is normal, scales and lines are observed but no cracks are found, and there is no obvious change in the hair shaft, it is judged that the person has not been in close contact with the fire source.
[0022] The method proposed by the present invention for judging whether a person is in close contact with a fire source based on slight heat damage to hair has the following beneficial effects:
[0023] The present invention proposes a new technical identification method for physical evidence of personal identification, which determines whether a person has been in close contact with a fire source and has been present at a fire scene when a fire occurs and develops through thermal damage to human hair. It has strong evidentiary power and is of great significance for inspection and identification, and expands the investigative technology of criminal investigators in fire-related cases. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 This is a comparison of the hair before and after radiant heat treatment;
[0025] Figure 2 It is the morphological characteristics of hair thermal damage marks observed by optical microscope under different heating conditions;
[0026] Figure 3 Scanning electron microscope (SEM) observation of hair results;
[0027] Figure 4 This is a test photo of extracting hair evidence in step 1 of an embodiment of the present invention;
[0028] Figure 5 This is a test photograph of the epidermis of the hair sample observed by scanning electron microscope (SEM) after gold spraying in step 2 of the embodiment of the present invention;
[0029] Figure 6It is a comparative observation diagram of the abnormal area observed by SEM magnification observation in step 3 to step 6 of the embodiment of the present invention (where the left side is an observation diagram with a SEM magnification of 500-1000 times, and the right side is an observation diagram with a corresponding SEM magnification greater than 1000 times);
[0030] Figure 7 It is a comparative observation diagram of another abnormal area observed by SEM magnification observation in step 3 to step 6 of the embodiment of the present invention (wherein the left side is an observation diagram with a SEM magnification of 500-1000 times, and the right side is an observation diagram with a corresponding SEM magnification of more than 1000 times);
[0031] Figure 8 The slight thermal damage traces of the embodiment of the present invention are gradually enlarged and observed by SEM (the magnifications are 100 times, 500 times, 1000 times, and 8000 times respectively);
[0032] Fig. 9 This is an example of slight heat damage marks on human hair, which is used to quantify and explain the damage marks in detail. DETAILED DESCRIPTION
[0033] The following is combined with Figure 1-9 The present invention is further described in detail with specific implementations to facilitate a clear understanding of the present invention, but they do not constitute a limitation on the present invention.
[0034] Example 1
[0035] Figure 1 This is a comparison of intact hair before and after radiation heat treatment. The hair was subjected to different heat treatments by adjusting the different radiation heat powers of the cone calorimeter. The heating time was 1.5s, and the ambient temperature was marked on the top. It can be seen that when the heat treatment temperature is 280℃-320℃, some hair has very obvious signs of heat damage, but there is still hair that is similar to the shape before heat treatment, and it is difficult to observe the signs of heat damage with the naked eye. Accordingly, this phenomenon shows that investigators sometimes find it difficult to determine whether the suspect's hair has been subjected to high temperatures when the conditions are unknown.
[0036] Figure 2 The morphological characteristics of hair thermal damage marks observed under different heating conditions using an optical microscope. Figure 2In the figure, a1 is the top of the hair magnified at 100×, a2 is the top of the hair magnified at 500×, a3 is the hair shaft magnified at 500×, b is the hair after heat treatment, and c is the hair that is obviously damaged after heat treatment. The temperature is marked above the image, and the magnification is provided in the lower right corner. It can be seen that at the same heat treatment temperature, the formation of heat damage marks on the hair is not certain, and the characteristics of some heat-treated hair and untreated hair after optical microscopic static observation are not much different, which also confirms that Figure 1 conclusion.
[0037] Figure 3 Figures a, b, and c show images of intact hair and heat-treated hair observed under a scanning electron microscope, with the heat treatment temperature marked in the lower right corner. It can be seen that the original hair is intact and straight, the top is normal, scales and lines are observed, but no cracks are found, and there are no obvious changes in the hair shaft. The hair that was obviously damaged by heat is bent, the diameter of the top and shaft is significantly increased and expanded, and the hair cuticle is broken. In severe areas, we found that the hair cuticle is completely cracked, exposing the hair cortex.
[0038] For hair that did not show obvious thermal damage by naked eye observation, scanning electron microscopy was used to examine the hair at a higher magnification (2×10 3 to 10×10 3 ) under observation (such as Figure 3 c), we found: the cleavage or separation of the multi-layer structure of the hair cuticle. The separation between adjacent hair scales. The damage to the surface of individual hair scales. These marks were mainly observed in the hair shaft rather than the tip. Analysis showed that these marks can be attributed to the tension caused by the hair bending and expanding due to heat loss of water, as well as the high temperature causing the hair to be broken and decomposed. It can be determined that the hair has suffered slight heat damage, and the marks can provide a basis for investigators to determine whether a person has been in close contact with a heat source.
[0039] Therefore, it is necessary to adopt a method of this embodiment based on slight thermal damage to hair to judge whether a person is in close contact with a fire source. Figure 4-6 , as shown in 8, including the following steps:
[0040] Step 1: If Figure 4 As shown, hair evidence was extracted.
[0041] Step 2: If Figure 5 As shown, after the hair sample was sprayed with gold, its epidermis was observed by scanning electron microscope (SEM), and the epidermis was the stratum corneum.
[0042] Step 3: If Figure 6 As shown, the scanning electron microscope (SEM) has a magnification of 500-1000 times. After focusing on the epidermis, the hair scales distributed on the surface of the hair can be observed.
[0043] Step 4: Look for surface abnormalities along the hair shaft that may have caused slight thermal damage. Surface abnormalities include hair shaft bends, local enlargement of the straight well, and irregular protrusions, etc. Search at the bends in the hair shaft and where the diameter is locally enlarged.
[0044] Step 5: For the abnormal areas, adjust and increase the magnification of the scanning electron microscope (SEM) to observe the hair cuticle scales. The adjusted and increased magnification of the scanning electron microscope (SEM) is greater than 1000 times to further analyze the trace characteristics of the details.
[0045] like Figure 8 As shown, these are observation images with magnifications of 100 times, 500 times, 1000 times, and 8000 times, respectively, which can determine whether a person is in close contact with a fire source based on slight thermal damage to the hair.
[0046] Step 6: Observe and record the signs of hair scale cracking, separation, and cracks on the epidermis, and then judge whether the person is in close contact with the fire source. The specific judgment method is:
[0047] Focus on the areas where the hair is curved, the diameter of the tip and shaft of the hair is significantly increased and expanded, and check whether there are any Fig. 9 Slight traces of heat damage shown:
[0048] The hair scales are broken in multiple layers, which is manifested as the hair cuticle is broken or the hair cuticle is completely split, exposing the hair cortex layer and the hair cuticle layer has a multi-layer structure of cracking or separation;
[0049] Long surface cracks, which appear as fine cracks with a length of more than 10 microns, a width of less than 1 micron and spanning several scales, or cracks with a length of between 5-10 microns, spanning several scales and a width of more than 1 micron;
[0050] Fine cracks appear as fine cracks on a single hair scale with a length of 5 microns, a width greater than or equal to 1 micron, and a depth of only the thickness of one hair scale.
[0051] If the first type plus the second or third typical slight heat damage signs mentioned above are found in the area at the same time, it is judged that the person has been in close contact with the fire source; if only the second or third typical slight heat damage signs are found, it can be inferred that the suspect may have been in close contact with the fire source; and when the hair is intact and straight, the top is normal, scales and lines are observed but no cracks are found, and there is no obvious change in the hair shaft, it is judged that the person has not been in close contact with the fire source.
[0052] Example 2
[0053] In this embodiment, Figure 7 As shown, the SEM magnified observation of another abnormal area observed in step 3 to step 6 of this embodiment is shown. The identification steps are the same as those in embodiment 1 and will not be described in detail here.
[0054] The above is only a preferred embodiment of the present invention, and does not impose any formal limitation on the structure of the present invention. The layout type and the number of uses of the present invention are not limited to this example, and can be optimized and selected according to the actual project. Any modification, equivalent change and decoration of the above embodiment based on the technical principle of the present invention that does not deviate from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.
Claims
1. A method for judging whether a person has been in close contact with a fire source based on slight heat damage to the hair, characterized in that: The steps include: Step 1: Extract hair evidence; Step 2: After the hair sample is sprayed with gold, its epidermis is observed by scanning electron microscope (SEM); Step 3: The SEM magnification is 500-1000 times, focusing on the epidermis to observe the hair scales distributed on the surface of the hair; Step 4: searching along the hair shaft for areas with surface abnormalities that may cause slight thermal damage, focusing on the bends of the hair shaft and the areas where the diameter is locally enlarged; in step 4, the surface abnormalities include areas of bends of the hair shaft, local enlargements of the diameter, and irregular protrusions; Step 5: For the abnormal area, adjust and increase the magnification of the scanning electron microscope (SEM) to observe the hair cuticle of the hair cortex; in the step 5, the magnification of the scanning electron microscope (SEM) after adjustment and increase is greater than 1000 times, and further analyze the trace characteristics of the details; Step 6: Observe and record the signs of hair scale cracking, separation, and cracks in the epidermis, and then judge whether the person is in close contact with the fire source; in step 6, the specific judgment method is: focus on the areas where the hair is bent, the diameter of the top and shaft of the hair is significantly increased and expanded, and find out whether there are the following types of slight heat damage signs in this area: The first type: multi-layer rupture of the hair scales, manifested as the rupture of the hair cuticle or the complete splitting of the hair cuticle, exposing the hair cortex and the multi-layer structure of the hair cuticle cracking or separation; The second type: long cracks on the surface, which are fine cracks with a length of more than 10 microns, a width of less than 1 micron and spanning several hair scales, or cracks with a length of between 5-10 microns, spanning several hair scales and a width of more than 1 micron; The third type: fine cracks, which appear as fine cracks on a single hair scale with a length of 5 microns, a width greater than or equal to 1 micron, and a depth of only the thickness of a layer of hair scales; If the first type plus the second or third type of typical slight heat damage are found in the area at the same time, it is judged that the personnel have close contact with the fire source; If only the second or third typical signs of slight heat damage are found, it can be inferred that the suspect may have had close contact with a fire source; when the hair is intact and straight, the top is normal, scales and lines are observed but no cracks are found, and there are no obvious changes in the hair shaft, it can be judged that the person has not had close contact with a fire source.
2. A method for determining whether a person has been in close contact with a fire source based on slight heat damage to hair according to claim 1, characterized in that: The epidermis layer observed in the step 2 is the stratum corneum of the epidermis.