An electrical fire evidence identity traceability identification method

Abstract

This invention belongs to the field of electrical fire evidence identification, specifically relating to a method for tracing the identity of electrical fire evidence. To improve the accuracy of identity tracing analysis of electrical fire evidence, this invention first removes exogenous interferences from the sample surface using non-polar and polar treatment agents, followed by digestion and elemental composition determination. Based on the elemental composition, each sample is preliminarily classified according to the on-site investigation, principal component analysis, or hierarchical cluster analysis. The preliminary classification results are then verified using linear discriminant analysis, and the group centroids of each category after preliminary classification are examined. When the preliminary classification results and verification results are consistent, samples representing categories with overlapping group centroids are considered to be identical, while samples representing categories with separated group centroids are considered not to be identical.

Description

Technical Field

[0001] This invention belongs to the field of electrical fire evidence identification, specifically involving a method for tracing the identity of electrical fire evidence. Background Technology

[0002] Electrical fire evidence identification is crucial for determining the cause of a fire, reducing the incidence of major and catastrophic fires, and minimizing fire losses. However, the complex wiring layout within buildings sometimes results in multiple power supply, power consumption, and communication equipment lines or cables being laid along the same conduit or shaft, increasing fire hazards. In such fires, multiple lines may melt, stick together, or break, or even burn into several sections, making it impossible to determine the specific purpose of the lines. Fire investigations may only yield traces of melting, and because the specific purpose of the electrical wiring before the fire cannot be traced, it's impossible to pinpoint which line or connected equipment malfunctioned. Consequently, fire investigators may only conclude that the fire was caused by an "electrical fault," unable to delve deeper into the cause. This complicates fire scene investigation and evidence identification, increasing the difficulty of fire investigation and cause determination, and consequently, complicating subsequent fire prevention and control efforts. Therefore, identifying the identity of key electrical fire evidence is of great significance for determining the cause of fire, reducing the incidence of major and serious fire accidents, and minimizing fire losses.

[0003] However, there are currently no precise identification methods, either domestically or internationally, for tracing the identity of physical evidence in electrical fires, nor can corresponding technical support be provided. There is no accurate and reliable identification technology to determine whether burnt wires or broken ends in a fire originated from the same wire. This makes it impossible to determine the identity of many pieces of physical evidence extracted from fire scenes, and also fails to provide technical support to fire scene investigators. This has long been a difficult problem for fire investigators and physical evidence identification personnel.

[0004] The main analytical methods for identifying the identity of electrical fire evidence include: (1) Macroscopic comparison method, which is mainly used to measure whether the diameter of a single wire is the same and whether the number of strands of a multi-strand wire is the same. However, this method has too low a distinguishing power and can only be used for rough screening on site, and cannot be used as an identification conclusion. (2) EDS method, which can only identify the surface element composition of electrical components. For example, copper wires can usually only identify copper, carbon and oxygen, and have no distinguishing power for wires of different brands. (3) XRD method, which is mainly used to analyze the phase composition of crystalline materials. However, electrical fire evidence such as wires are mostly pure metal single phases (such as pure copper and pure aluminum). XRD can only confirm their crystal structure and has limited value for attribution analysis. (4) XRF method, which can quickly distinguish the substrate type of electrical fire evidence (such as copper and aluminum). However, its limitations in detecting light elements, being affected by matrix effects, having high requirements for sample surface and being unable to provide phase information determine that it is more suitable as a preliminary screening and macroscopic component analysis tool in the source tracing analysis of electrical fire evidence.

[0005] In addition to the main components, most electrical components contain various associated elements. The composition and content of these elements constitute the "fingerprint" of the electrical component, which is expected to serve as a criterion for tracing the identity of electrical fire evidence, compensating for the shortcomings of the aforementioned technical methods and establishing a precise and reliable identification method. However, it should be noted that electrical fire evidence, after being subjected to high temperatures, collapse, burial, etc., usually forms a large amount of carbon layer and other exogenous components on its surface. If not cleaned thoroughly, this will greatly interfere with the trace element analysis of electrical fire evidence and directly affect the accuracy of identity tracing analysis. Currently, there is no systematic research on methods for treating exogenous interfering substances on the surface of electrical fire evidence, nor are there any dedicated treatment agents developed. Summary of the Invention

[0006] To address the industry challenge of lacking accurate and reliable methods for identifying the identity of physical evidence in electrical fires, this invention provides a method for identifying the identity of physical evidence in electrical fires, comprising the following:

[0007] After removing external interferences from the surface of each sample, the samples are digested and their elemental composition is determined. Based on the elemental composition of each sample, a preliminary classification is performed using on-site investigation, principal component analysis, or hierarchical cluster analysis. The preliminary classification results are then verified using linear discriminant analysis, and the centroids of each group after preliminary classification are examined. When the preliminary classification results and verification results are consistent, samples represented by groups with overlapping centroids are considered to have the same identity (same source / from the same conductor), while samples represented by groups with separate centroids are considered not to have the same identity.

[0008] Furthermore, when the preliminary classification results and the verification results are inconsistent, the preliminary classification is re-performed until the final preliminary classification results and the verification results are completely consistent, and then the group centroids of each category are examined.

[0009] External interference includes non-polar external interference and polar external interference;

[0010] The sample to be tested is immersed in a non-polar treatment agent to remove non-polar exogenous interferences. The non-polar treatment agent is a solution of cyclohexane and toluene with a volume percentage of (50%~80%): (20%~50%), and ultrasonic vibration is performed during the immersion process. Then the sample is immersed in a polar treatment agent to remove polar exogenous interferences. The polar treatment agent is a solution of dimethylchlorosilane and tetrahydrofuran with a volume percentage of (10%~30%): (70%~90%), and ultrasonic vibration is performed during the immersion process.

[0011] After removing exogenous interferences from the sample surface, at least two sampling points at different locations on the same sample are selected for digestion in the digestion solution, with each sampling point containing 50mg to 100mg. The digestion solution includes hot nitric acid (for aluminum wires, brass connectors, etc., in addition to nitric acid, a small amount of hydrochloric acid or sulfuric acid can be added to aid dissolution). After complete digestion, the sample is evaporated to dryness, and deionized water is added to make up the volume. The elemental composition of the sample is then determined.

[0012] The elemental composition of the sample was determined by inductively coupled plasma atomic absorption spectrometry. The sample elemental composition included several elements from B, Mg, Si, P, Sc, V, Cr, Mn, Co, Ni, Ga, As, Sr, Mo, Pd, Cd, Sb, Ba, Ce, Ho, Pt, Au, Hg, Ti, and Pb. Ten to twenty elements were selected for preliminary classification, with priority given to elements with similar contents, while elements with excessively high or low contents were removed.

[0013] The beneficial effects of this invention are as follows:

[0014] (1) This invention provides a precise quantitative identity tracing and identification technology for electrical fire evidence. Based on the distribution characteristics of trace elements in electrical fire evidence and combined with chemometrics methods, it realizes the attribution analysis of electrical fire evidence. This is not only conducive to thoroughly investigating the cause of the fire and clarifying the responsibility for the accident, but can also be applied to the subsequent rectification of fire hazards, reducing the incidence of major and serious fire accidents and minimizing fire losses.

[0015] (2) This invention provides quantitative identification and analysis, minimizing human interference and ensuring objectivity and impartiality. The required sample volume for digestion is small, only 50mg~100mg, and electrical fire evidence often has low residual amounts (such as molten beads, sometimes less than 1mm in diameter), making this invention highly applicable. The identification conclusions are presented in two-dimensional and three-dimensional formats, making them clear and easy to understand.

[0016] (3) This invention establishes a cleaning process for electrical fire evidence and forms an electrical fire cleaning agent formula. In particular, the addition of dimethylchlorosilane in the polar treatment agent can react with the trace amount of water dissolved in tetrahydrofuran to produce HCl, which has a slight etching effect on the surface of electrical fire evidence. This is beneficial for the removal of attached exogenous interferences and automatically removes the oxide film formed on the surface of electrical fire evidence under high temperature. This allows the test data to truly reflect the elemental composition of the electrical fire evidence itself and greatly improves the accuracy of the identification results. Attached Figure Description

[0017] Figure 1 The image shows an aluminum wire specimen submitted for testing at a fire scene in Shenyang, as shown in Example 1.

[0018] Figure 2 This is a photograph of the multi-strand aluminum wire evidence submitted for testing at a fire scene in Henan Province, as shown in Example 1.

[0019] Figure 3 This is a two-dimensional display of the identity traceability analysis results of each sample in Example 1;

[0020] Figure 4 This is a diagram of the multi-strand wire evidence submitted for testing at a fire scene in Shandong Province, as shown in Example 2.

[0021] Figure 5 This is a two-dimensional display of the source identification analysis results for each sample in Example 2;

[0022] Figure 6 This is a three-dimensional representation of the source identification analysis results for each sample in Example 2;

[0023] Figure 7 The image shows a welded iron component that was submitted for inspection at a fire scene in Shenyang, as shown in Example 3.

[0024] Figure 8 This is a two-dimensional display of the identity traceability analysis results of each sample in Example 3;

[0025] Figure 9 This is a diagram of the wire evidence submitted for testing at a fire scene in Jilin Province, as shown in Example 4.

[0026] Figure 10 This is a diagram showing the centroid separation effect of the three sample groups in Example 4;

[0027] Figure 11 This is a graph showing the verification results of the linear discriminant analysis in Example 4;

[0028] Figure 12 This is a two-dimensional display of the identity traceability analysis results of each sample in Example 4;

[0029] Figure 13 This is a three-dimensional representation of the source identification analysis results for each sample in Example 4;

[0030] Figure 14 This is a diagram of the wire evidence submitted for testing at a fire scene in Liaoning Province, as shown in Example 5.

[0031] Figure 15 This is a diagram showing the centroid separation effect of the three sample groups in Example 5;

[0032] Figure 16 This is a two-dimensional display of the identity traceability analysis results of each sample in Example 5;

[0033] Figure 17 This is a three-dimensional representation of the source identification analysis results for each sample in Example 5;

[0034] Figure 18 This is a diagram of the conductor evidence submitted for testing at the scene of a forest fire in Sichuan Province, as shown in Example 6.

[0035] Figure 19 This is a diagram showing the centroid separation effect of the four sample groups in Example 6;

[0036] Figure 20 This is a two-dimensional display of the identity traceability analysis results of each sample in Example 6;

[0037] Figure 21 This is a three-dimensional representation of the source identification analysis results for each sample in Example 6;

[0038] Figure 22 This is a diagram of the conductor evidence submitted for testing at a fire scene in Inner Mongolia, as shown in Example 7.

[0039] Figure 23 This is a diagram showing the numbering of each wire in sample JC4 in Example 7;

[0040] Figure 24 This is a diagram showing the centroid separation effect of the five sample groups in Example 7;

[0041] Figure 25 This is the verification chart for the linear discriminant analysis in Example 7;

[0042] Figure 26 This is a two-dimensional display of the source identification analysis results for each sample in Example 7;

[0043] Figure 27This is a three-dimensional representation of the source identification analysis results for each sample in Example 7;

[0044] Figure 28 This is a diagram of the conductor evidence submitted for testing at a fire scene in Hebei Province, as shown in Example 8.

[0045] Figure 29 This is a diagram showing the centroid separation effect of the ten sample groups in Example 8;

[0046] Figure 30 This is a two-dimensional display of the identity traceability analysis results of each sample in Example 8;

[0047] Figure 31 This is a three-dimensional representation of the source identification analysis results for each sample in Example 8;

[0048] Figure 32 The following are the EDS spectra of two fallen welded iron pieces found on different floors in Comparative Example 1; where (a) is 18# and (b) is 20#.

[0049] Figure 33 The following are the EDS spectra of different samples in Comparative Example 2; where (a) is JC1, (b) is JC2, (c) is JC3, and (d) is JC401.

[0050] Figure 34 A three-dimensional representation of the identity traceability analysis results of the samples in Comparative Example 3 without the use of dimethylchlorosilane;

[0051] Figure 35 A three-dimensional representation of the identity traceability analysis results of the sample treated with excess dimethylchlorosilane in Comparative Example 4;

[0052] Figure 36 A three-dimensional representation of the source identification analysis results of the samples used in Comparative Example 5 when 25 elements were analyzed.

[0053] Figure 37 This is a three-dimensional representation of the source identification analysis results of the samples used in Comparative Example 6 when eight elements were analyzed. Detailed Implementation

[0054] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described in this invention are only for further explanation and illustration, and not for limiting their application scope. Based on this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0055] Figure 4 , Figure 9 , Figure 14 , Figure 18 , Figure 28 The text mainly refers to the numbering of the samples by the fire and rescue department when the samples were sent for testing, and is unrelated to the invention. The sample numbers in each figure have been explained in the corresponding embodiments.

[0056] Example 1

[0057] right Figure 1 The aluminum wires submitted for testing at the scene of a fire in Shenyang are numbered 01#, 02#, and 03#. Figure 2 The evidence submitted from the fire scene in Henan Province, consisting of multiple strands of aluminum wires numbered 11#, 12#, 13#, and 14#, was used for identification to trace their origin.

[0058] S1 Preprocessing:

[0059] (a) Wipe the surface of the sample to be tested with a paper towel to remove macroscopically visible impurities such as carbides.

[0060] (b) Immerse the sample to be tested in a non-polar treatment agent prepared with cyclohexane and toluene, each accounting for 50% of the total volume, and sonicate for 3 minutes to remove the non-polar exogenous interferences remaining on the sample surface.

[0061] (c) The sample to be tested is then immersed in a polar treatment agent prepared with dimethylchlorosilane (CAS No. 1066-35-9) and tetrahydrofuran, with the volume ratios of the two being 10% and 90%, respectively, and ultrasonically vibrated for 3 min to remove polar exogenous interferences from the sample surface.

[0062] (d) The sample to be tested is then immersed in deionized water for cleaning, ultrasonically vibrated for 1 minute, and filtered; the cleaning is repeated 3 times; the sample surface moisture is absorbed with filter paper and then dried at 80°C to constant weight.

[0063] S2 detection and analysis:

[0064] (e) Digestion: For each pretreated sample, three sampling points at different locations were selected as specimens. 50 mg to 100 mg of each specimen was accurately weighed and placed in a volumetric flask. A small amount of nitric acid and hydrochloric acid were added and heated for digestion. After the sample was completely digested, the acid was evaporated to dryness, and the sample was allowed to cool to room temperature before adding deionized water to make up to the final volume.

[0065] (f) Determination of elemental composition: The elemental composition of the sample was determined using inductively coupled plasma mass spectrometry. Fifteen elements with similar content were selected for further analysis: B, Mg, P, Sc, Mn, Co, Ga, As, Sr, Pd, Cd, Sb, Ho, Ti, and Pb.

[0066] (g) Preliminary classification: Hierarchical cluster analysis was used to preliminarily classify samples 01#, 02#, and 03#. The results showed that samples 01# to 03# each belonged to their own category; samples 11# to 14# were classified into one category based on their source; a total of four categories.

[0067] (h) Verification and examination of group centroids: Linear discriminant analysis was used to analyze and verify the above four types of samples. The verification results were completely consistent with the preliminary classification results, indicating that the classification was accurate. Among them, sample 01# was classified as class 1, sample 02# as class 2, sample 03# as class 3, and samples 11#~14# as class 4.

[0068] The linear discriminant analysis results were imported into Origin plotting software and plotted as a two-dimensional spectrum. The identification results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the centroids of sample groups 11# to 14# coincide, clustering in the two-dimensional spectrum, proving that the evidence 11# to 14# shares the same identity. The centroids of the four sample groups are separated, discrete in the two-dimensional spectrum, proving that the four sample groups do not share the same identity; that is, samples 01#, 02#, 03#, and 11# to 14# do not share the same identity. It is worth noting that although samples 1# and 3# are close in the two-dimensional spectrum, their centroids are separated, and they cannot be classified as the same conductor. Furthermore, among samples 11# to 14#, 11# to 13# are of the same conductor, while 14# is of a different conductor, indicating that even multi-strand conductors can be classified as the same type, i.e., have the same origin. This also proves that the method of this invention is applicable not only to single-strand conductors but also to multi-strand conductors. Verification by the fire and rescue department confirms that the above conclusions are consistent with the actual situation, and the identification method is accurate and effective.

[0069] Example 2

[0070] right Figure 4 The evidence of multiple strands of wire submitted for testing at the scene of a fire in Zhongshan, Shandong Province, includes samples numbered 5# on the left and 7# on the right, as well as copper wires from different origins and brands, which were used for identity tracing. Sample 8# is a ZR-BV wire from Beijing Xinghui, sample 9# is a ZD-BV wire from Liaoning Jinda, and sample 10# is a ZRBV wire from Beijing Jiayang.

[0071] S1 Preprocessing:

[0072] (a) Wipe the surface of the sample to be tested with a paper towel to remove macroscopically visible impurities such as carbides.

[0073] (b) Immerse the sample in a non-polar treatment agent prepared with cyclohexane and toluene, with the volume ratios of the two being 80% and 20%, respectively, and sonicate for 3 minutes to remove residual non-polar exogenous interferences on the sample surface.

[0074] (c) The sample to be tested is then immersed in a polar treatment agent prepared with dimethylchlorosilane and tetrahydrofuran, with the volume ratios of the two being 30% and 70%, respectively, and ultrasonically vibrated for 3 minutes to remove surface polar external interferences.

[0075] (d) The sample to be tested is then immersed in deionized water for cleaning, ultrasonically vibrated for 1 minute, and filtered; the cleaning is repeated 3 times; the sample surface moisture is absorbed with filter paper and then dried at 80°C to constant weight.

[0076] S2 detection and analysis:

[0077] (e) Digestion: Four sampling points at different locations were selected from each of the pretreated samples as specimens. 50 mg to 100 mg of each specimen was accurately weighed and placed in a volumetric flask. A small amount of nitric acid was added and the sample was heated for digestion. After the sample was completely digested, the acid was evaporated to dryness, and the sample was allowed to cool to room temperature before adding deionized water to make up to the final volume.

[0078] (f) Determination of elemental composition: The elemental composition of the sample was determined using inductively coupled plasma mass spectrometry. Twenty elements with similar content were selected for further analysis: B, Mg, Si, P, Sc, Cr, Mn, Co, Ga, As, Sr, Mo, Pd, Cd, Sb, Ho, Au, Hg, Ti, and Pb.

[0079] (g) Preliminary classification: Using principal component analysis, samples 5# and 7# were each classified into a separate class. Based on the sample source, samples 8#, 9#, and 10# were each classified into a separate class, for a total of five classes.

[0080] (h) Verification and examination of group centroids: Linear discriminant analysis was used to analyze and verify the above five types of samples. The verification results were completely consistent with the preliminary classification results, indicating that the classification was accurate. Among them, sample #5 was classified as class 1, sample #7 as class 2, sample #8 as class 3, sample #9 as class 4, and sample #10 as class 5.

[0081] The linear discriminant analysis results were imported into Origin plotting software and plotted as two-dimensional and three-dimensional spectra. The identification results are as follows: Figure 5 and Figure 6 As shown, the centroids of the five sample groups do not overlap and are discrete in the two-dimensional and three-dimensional spectra, indicating that the five sample groups are not identical to each other; that is, samples 5#, 7#, 8#, 9#, and 10# are not identical. The above conclusions have been verified and confirmed by the fire and rescue department and are consistent with the actual situation, demonstrating the accuracy and effectiveness of the identification method.

[0082] Example 3

[0083] right Figure 7Two pieces of welded iron, found on different floors at the scene of a fire caused by welding in Shenyang, were identified as identical during a source tracing analysis. Figure 7 Two sections, numbered 18# and 19#, were cut from the welded iron part on the left side, and one section, numbered 20#, was cut from the welded iron part on the right side.

[0084] S1 Preprocessing:

[0085] (a) Wipe the surface of the sample to be tested with a paper towel to remove macroscopically visible impurities such as carbides.

[0086] (b) Immerse the sample to be tested in a non-polar treatment agent prepared with cyclohexane and toluene, with the volume ratios of the two being 60% and 40%, respectively, and sonicate for 3 minutes to remove the non-polar exogenous interferences remaining on the sample surface.

[0087] (c) The sample to be tested is then immersed in a polar treatment agent prepared with dimethylchlorosilane and tetrahydrofuran, with the volume ratios of the two being 20% ​​and 80%, respectively, and ultrasonically vibrated for 3 minutes to remove polar exogenous interferences from the sample surface.

[0088] (d) The sample to be tested is then immersed in deionized water for cleaning, ultrasonically vibrated for 1 minute, and filtered; the cleaning is repeated 3 times; the sample surface moisture is absorbed with filter paper and then dried at 80°C to constant weight.

[0089] S2 detection and analysis:

[0090] (e) Digestion: For each pretreated sample, two sampling points at different locations were selected as specimens. 50mg to 100mg of each specimen was accurately weighed and placed in a volumetric flask. A small amount of nitric acid was added and the sample was heated for digestion. After the sample was completely digested, the acid was evaporated to dryness, and the sample was allowed to cool to room temperature before adding deionized water to make up to the final volume.

[0091] (f) Determination of elemental composition: The elemental composition of the sample to be tested was determined using an inductively coupled plasma mass spectrometer. Ten elements with similar content were selected for further analysis: B, V, Co, Ni, Ga, As, Ba, Ce, Pt, and Pb.

[0092] (g) Preliminary classification: Hierarchical cluster analysis was used to preliminarily classify samples 18#, 19#, and 20#. The results showed that samples 18# and 19# could be classified into one class, and sample 20# could be classified into another class, for a total of two classes.

[0093] (h) Verification and examination of group centroids: Linear discriminant analysis was used to analyze and verify the two types of samples. The verification results were completely consistent with the preliminary classification results, indicating that the classification was accurate. Among them, samples 18# and 19# were classified into class 1, and sample 20# was classified into class 2.

[0094] The linear discriminant analysis results were imported into Origin plotting software and plotted as a two-dimensional spectrum. The identification results are as follows: Figure 8 As shown (the blank sample in the figure refers to a blank solution without the analyte added). From Figure 8 It is evident that the centroids of sample groups #18 and #19 coincide and cluster in the two-dimensional spectrum, proving that samples #18 and #19 are of the same identity. Conversely, the centroids of the two sample groups are separated and discrete in the two-dimensional spectrum, proving that these two sample groups are not of the same identity; that is, samples #18 and #19 are not of the same identity as sample #20. Verification by the fire and rescue department confirms that the above conclusions are consistent with the actual situation, and the identification method is accurate and effective.

[0095] Example 4

[0096] right Figure 9 Five wires, numbered JC-1 to JC-5, were extracted from the ignition point of a fire in a certain area of ​​Jilin Province, China, and were used for identification to trace their origin.

[0097] S1 Preprocessing:

[0098] (a) Wipe the surface of the sample to be tested with a paper towel to remove macroscopically visible impurities such as carbides.

[0099] (b) Immerse the sample to be tested in a non-polar treatment agent prepared with cyclohexane and toluene, with the volume ratios of the two being 70% and 30%, respectively, and sonicate for 3 minutes to remove the non-polar exogenous interferences remaining on the sample surface.

[0100] (c) Immerse the sample to be tested in a polar treatment agent prepared with dimethylchlorosilane and tetrahydrofuran, with the volume ratios of the two being 28% and 72%, respectively, and sonicate for 3 min to remove polar exogenous interferences from the sample surface.

[0101] (d) Soak the sample to be tested in deionized water for cleaning, ultrasonically vibrate for 1 min, and filter; repeat the cleaning 3 times; after blotting the surface moisture of the sample with filter paper, dry it at 80°C to constant weight.

[0102] S2 detection and analysis:

[0103] (e) Digestion: For each pretreated sample, three sampling points at different locations were selected as samples. 50 mg to 100 mg of each sample was accurately weighed and placed in a volumetric flask. A small amount of nitric acid was added and the sample was heated for digestion. After the sample was completely digested, the acid was evaporated to dryness, and the sample was allowed to cool to room temperature before adding deionized water to make up to the final volume.

[0104] (f) Determination of elemental composition: The elemental composition of the sample was determined using inductively coupled plasma mass spectrometry. Fifteen elements with similar content were selected for further analysis: B, Mg, P, V, Co, Ni, Ga, As, Mo, Sb, Ba, Ce, Pt, Hg, and Pb.

[0105] (g) Preliminary classification: Hierarchical cluster analysis was used to preliminarily classify samples JC-1 to JC-5. The results showed that sample JC-1 could be classified into one class; samples JC-2 and JC-3 could be classified into another class; and samples JC-4 and JC-5 could be classified into another class; for a total of three classes.

[0106] (h) Verification and examination of group centroids: Linear discriminant analysis was used to analyze and verify the above three types of samples. The verification results were completely consistent with the preliminary classification results, indicating that the classification was accurate. Figure 10 , Figure 11 As shown in the figure. Among them, sample JC-1 is classified as category 1, samples JC-2 and JC-3 are classified as category 2, and samples JC-4 and JC-5 are classified as category 3.

[0107] The linear discriminant analysis results were imported into Origin plotting software and plotted as a two-dimensional spectrum. The identification results are as follows: Figure 12 and Figure 13 As shown. By Figure 12 and Figure 13 It is evident that the centroids of sample groups JC-2 and JC-3 coincide and cluster in the two-dimensional / three-dimensional spectra, proving that samples JC-2 and JC-3 are related. Similarly, the centroids of sample groups JC-4 and JC-5 coincide and cluster in the two-dimensional / three-dimensional spectra, proving that samples JC-4 and JC-5 are related. Furthermore, the centroids of the three sample groups are separated from each other and are discrete in the two-dimensional / three-dimensional spectra, proving that the three sample groups are not related to each other; that is, samples JC-2 and JC-3, samples JC-4 and JC-5, and sample JC-1 are not related. Verification by the fire and rescue department confirms that the above conclusions are consistent with the actual situation, and the identification method is accurate and effective.

[0108] Example 5

[0109] right Figure 14 Five wires, numbered JC1 to JC5, were extracted from the ignition point of a fire in a certain area of ​​Liaoning Province, and their identity was traced for identification.

[0110] S1 Preprocessing:

[0111] (a) Wipe the surface of the sample to be tested with a paper towel to remove macroscopically visible impurities such as carbides.

[0112] (b) Immerse the sample to be tested in a non-polar treatment agent prepared with cyclohexane and toluene, with the volume ratios of the two being 65% and 35%, respectively, and sonicate for 3 minutes to remove the non-polar exogenous interferences remaining on the sample surface.

[0113] (c) The sample to be tested is then immersed in a polar treatment agent prepared with dimethylchlorosilane and tetrahydrofuran, with the volume ratios of the two being 25% and 75%, respectively, and ultrasonically vibrated for 3 minutes to remove polar exogenous interferences from the sample surface.

[0114] (d) The sample to be tested is then immersed in deionized water for cleaning, ultrasonically vibrated for 1 minute, and filtered; the cleaning is repeated 3 times; the sample surface moisture is absorbed with filter paper and then dried at 80°C to constant weight.

[0115] S2 detection and analysis:

[0116] (e) Digestion: Three sampling points at different locations were selected from each of the pretreated samples as specimens. 50 mg to 100 mg of each specimen was accurately weighed and placed in a volumetric flask. A small amount of nitric acid was added and the sample was heated for digestion. After the sample was completely digested, the acid was evaporated to dryness, and the sample was allowed to cool to room temperature before adding deionized water to make up to the final volume.

[0117] (f) Determination of elemental composition: The elemental composition of the sample was determined using inductively coupled plasma mass spectrometry. Twelve elements with similar content, namely Mg, Si, V, Co, Ga, Sr, Pd, Sb, Ce, Au, Hg and Pb, were selected for further analysis.

[0118] (g) Preliminary classification: Hierarchical cluster analysis was used to preliminarily classify samples JC1 to JC5. The results showed that JC1 could be classified into one category; JC2 and JC3 could be classified into another category; and JC4 and JC5 could be classified into another category; for a total of three categories.

[0119] (h) Verification and examination of group centroids: Linear discriminant analysis was used to analyze and verify the above three types of samples. The verification results were completely consistent with the preliminary classification results, indicating that the classification was accurate. Figure 15 As shown in the figure. Among them, sample JC1 is classified as Class 1, samples JC2 and JC3 are classified as Class 2, and samples JC4 and JC5 are classified as Class 3.

[0120] The linear discriminant analysis results were imported into Origin plotting software and plotted as a two-dimensional spectrum. The identification results are as follows: Figure 16 , Figure 17 As shown. By Figure 16 , Figure 17It is evident that the centroids of sample groups JC2 and JC3 coincide and cluster in the two-dimensional / three-dimensional spectra, proving that samples JC2 and JC3 are of the same identity. Similarly, the centroids of sample groups JC4 and JC5 coincide and cluster in the two-dimensional / three-dimensional spectra, proving that samples JC4 and JC5 are of the same identity. Furthermore, the centroids of the three sample groups are separated from each other and are discrete in the two-dimensional / three-dimensional spectra, proving that the three sample groups are not of the same identity; that is, samples JC2 and JC3, JC4 and JC5, and JC1 are not of the same identity. Verification by the fire and rescue department confirms that the above conclusions are consistent with the actual situation, and the identification method is accurate and effective.

[0121] Example 6

[0122] right Figure 18 Six conductor wire samples collected from the ignition point of a forest fire in Sichuan Province were subjected to identity verification based on their original fire department identification numbers: B1-1, B1-2, B2-1, B2-2, w1, and w2. Specifically, B1-1, B1-2, and w1 were all aluminum conductors, while B2-1, B2-2, and w2 were all copper conductors.

[0123] S1 Preprocessing:

[0124] (a) Wipe the surface of the sample to be tested with a paper towel to remove macroscopically visible impurities such as carbides.

[0125] (b) Immerse the sample to be tested in a non-polar treatment agent prepared with cyclohexane and toluene, with the volume ratios of the two being 55% and 45%, respectively, and sonicate for 3 minutes to remove the non-polar exogenous interferences remaining on the sample surface.

[0126] (c) The sample to be tested is then immersed in a polar treatment agent prepared with dimethylchlorosilane and tetrahydrofuran, with the volume ratios of the two being 25% and 75%, respectively, and ultrasonically vibrated for 3 minutes to remove polar exogenous interferences from the sample surface.

[0127] (d) The sample to be tested is then immersed in deionized water for cleaning, ultrasonically vibrated for 1 minute, and filtered; the cleaning is repeated 3 times; the sample surface moisture is absorbed with filter paper and then dried at 80°C to constant weight.

[0128] S2 detection and analysis:

[0129] (e) Digestion: Three sampling points at different locations were selected from each of the pretreated samples as specimens. 50mg to 100mg of each specimen was accurately weighed and placed in a volumetric flask. A small amount of nitric acid was added (for aluminum wires, a small amount of hydrochloric acid was added to aid dissolution), and the sample was heated for digestion. After the sample was completely digested, the acid was evaporated, and the sample was allowed to cool to room temperature before adding deionized water to make up to the final volume.

[0130] (f) Determination of elemental composition: The elemental composition of the sample was determined using inductively coupled plasma mass spectrometry. Sixteen elements with similar content were selected for further analysis: B, Mg, Si, Sc, V, Co, Ga, As, Sr, Pd, Sb, Ce, Au, Hg, Tl, and Pb.

[0131] (g) Preliminary classification: Based on the sample conductor type and combined with hierarchical cluster analysis, samples B1-1, B1-2, B2-1, B2-2, w1, and w2 were preliminarily classified. The results showed that samples B1-1 and w1 could be classified into one category, sample B1-2 into another category, samples B2-1 and w2 into another category, and sample B2-2 into yet another category; a total of four categories.

[0132] (h) Verification and examination of group centroids: Linear discriminant analysis was used to analyze and verify the above four types of samples. The verification results were completely consistent with the preliminary classification results, indicating that the classification was accurate. Figure 19 As shown in the figure. Among them, samples B1-1 and w1 are classified as category 1, sample B1-2 as category 2, samples B2-1 and w2 as category 3, and sample B2-2 as category 4.

[0133] The linear discriminant analysis results were imported into Origin plotting software and plotted as a two-dimensional spectrum. The identification results are as follows: Figure 20 , Figure 21 As shown. By Figure 20 , Figure 21 It is evident that the centroids of sample groups B1-1 and w1 coincide, and they cluster in the two-dimensional / three-dimensional spectra, proving that samples B1-1 and w1 are of the same identity. Similarly, the centroids of sample groups B2-1 and w2 coincide, and they cluster in the two-dimensional / three-dimensional spectra, proving that samples B2-1 and w2 are of the same identity. Furthermore, the centroids of the four sample groups are separated from each other, and they are discrete in the two-dimensional / three-dimensional spectra, proving that the four sample groups are not of the same identity, i.e., samples B1-1 and w1, B2-1 and w2, B1-2, and B2-2 are not of the same identity. Verification by the fire and rescue department confirms that the above conclusions are consistent with the actual situation, and the identification method is accurate and effective.

[0134] Example 7

[0135] right Figure 22Four electrical wire samples, numbered JC1 to JC4, were submitted for testing at the scene of a fire in Inner Mongolia. JC4 consisted of five wires scattered on the ground near the fire's origin. An identification and provenance analysis was conducted on these wires. A short circuit was detected in JC4. Three households had wires passing through the same location where the fire originated. Samples of these wires, numbered JC1, JC2, and JC3, were extracted from each household. The task was to compare the identification relationship between the JC4 wires and the aforementioned three household wires (JC1 to JC3) to determine which household's electrical fault caused the fire.

[0136] S1 Preprocessing:

[0137] (a) Wipe the surface of the sample to be tested with a paper towel to remove macroscopically visible impurities such as carbides.

[0138] (b) Immerse the sample to be tested in a non-polar treatment agent prepared with cyclohexane and toluene, with the volume ratios of the two being 75% and 25%, respectively, and sonicate for 3 minutes to remove the non-polar exogenous interferences remaining on the sample surface.

[0139] (c) The sample to be tested is then immersed in a polar treatment agent prepared with dimethylchlorosilane and tetrahydrofuran, with a volume ratio of 23% and 77%, respectively, and ultrasonically vibrated for 3 min to remove polar exogenous interferences from the sample surface.

[0140] (d) The sample to be tested is then immersed in deionized water for cleaning, ultrasonically vibrated for 1 minute, and filtered; the cleaning is repeated 3 times; the sample surface moisture is absorbed with filter paper and then dried at 80°C to constant weight.

[0141] S2 detection and analysis:

[0142] (e) Digestion: Two sampling points from different locations were taken from each pretreated sample as specimens. 50mg-100mg of each specimen was accurately weighed and placed in a volumetric flask. A small amount of nitric acid and hydrochloric acid were added, and the sample was heated for digestion. After complete digestion, the acid was evaporated to dryness, and the sample was allowed to cool to room temperature before adding deionized water to make up the volume. Since the sources of samples JC1-JC3 were clear, one wire was randomly selected from each numbered sample for specimen collection. Sample JC4 had a total of 5 wires, numbered JC401-JC405. Figure 23 As shown, each number represents a sample taken from the specimen.

[0143] (f) Determination of elemental composition: The elemental composition of the sample was determined using inductively coupled plasma mass spectrometry. Eighteen elements with similar content were selected for further analysis: Mg, Sc, V, Cr, Mn, Co, Ni, Ga, Sr, Mo, Pd, Cd, Sb, Ba, Ho, Pt, Au, and Pb.

[0144] (g) Preliminary classification: Hierarchical cluster analysis was used to preliminarily classify physical evidence samples JC1, JC2, JC3, JC401, JC402, JC403, JC404, and JC405. The results showed that physical evidence samples JC1, JC402, JC403, and JC404 could be classified into one category; JC2, JC3, JC401, and JC405 each formed another category; for a total of five categories.

[0145] (h) Verify and examine the group centroids: Linear discriminant analysis was used to analyze and verify the above five types of samples. The verification results were completely consistent with the preliminary classification results, indicating that the classification results were accurate. Figure 24 , Figure 25 As shown. Among them, samples JC1, JC402, JC403, and JC404 are classified as category 1, sample JC2 as category 2, sample JC3 as category 3, sample JC401 as category 4, and sample JC405 as category 5.

[0146] The linear discriminant analysis results were imported into Origin plotting software and plotted as a two-dimensional spectrum. The identification results are as follows: Figure 26 , Figure 27 As shown. By Figure 26 , Figure 27 It is evident that the centroids of sample groups JC1, JC402, JC403, and JC404 coincide, clustering in the two-dimensional / three-dimensional spectra, proving that samples JC1, JC402, JC403, and JC404 share a common identity. Conversely, the centroids of the five sample groups separate, discretizing in the two-dimensional / three-dimensional spectra, proving that the five sample groups do not share a common identity. Specifically, samples JC1, JC402, JC403, JC404, JC2, JC3, JC401, and JC405 do not share a common identity. These conclusions further prove that the fire was caused by an electrical fault in the JC1 conductor. Verification by the fire and rescue department confirmed that these conclusions are consistent with the actual situation, and the identification method is accurate and effective.

[0147] Example 8

[0148] right Figure 28 The wires submitted from the fire scene in Hebei Province were used for identification and source tracing. JC1 was the wire from the location where the fire originated; JC2-JC5 were purchased wires of the same brand as JC1 as control samples; JC6-JC9 were purchased wires of different brands but the same specifications as JC1 as control samples; and JC10-JC14 were wires of similar specifications retrieved from other rooms in different buildings that were not affected by the fire.

[0149] S1 Preprocessing:

[0150] (a) Wipe the surface of electrical fire evidence with a paper towel to remove macroscopically visible impurities such as carbon deposits.

[0151] (b) Immerse the sample in a non-polar treatment agent prepared with cyclohexane and toluene, with the volume ratios of the two being 62% and 38%, respectively, and sonicate for 3 minutes to remove residual non-polar exogenous interferences on the sample surface.

[0152] (c) The sample to be tested is then immersed in a polar treatment agent prepared with dimethylchlorosilane and tetrahydrofuran, with a volume ratio of 27% and 73%, respectively, and ultrasonically vibrated for 3 min to remove polar exogenous interferences from the sample surface.

[0153] (d) The sample to be tested is then immersed in deionized water for cleaning, ultrasonically vibrated for 1 minute, and filtered; the cleaning is repeated 3 times; the sample surface moisture is absorbed with filter paper and then dried at 80°C to constant weight.

[0154] S2 detection and analysis:

[0155] (e) Digestion: For each pretreated sample, three sampling points at different locations were selected as samples for analysis. 50 mg to 100 mg of each sample was accurately weighed and placed in a volumetric flask. A small amount of nitric acid was added and the sample was heated for digestion. After the sample was completely digested, the acid was evaporated to dryness, and the sample was allowed to cool to room temperature before adding deionized water to make up to the final volume.

[0156] (f) Determination of elemental composition: The elemental composition of the sample was determined using inductively coupled plasma mass spectrometry. Twenty elements with similar elemental contents, namely B, Si, Sc, V, Cr, Mn, Co, Ga, As, Sr, Mo, Pd, Cd, Ba, Ce, Ho, Pt, Hg, Ti, and Pb, were selected for further analysis.

[0157] (g-1) Preliminary classification (first time): Principal component analysis was first used to classify samples JC1 to JC14. The results showed that samples JC1 to JC3 clustered into one class, samples JC4 to JC5 clustered into one class, and samples JC6 to JC14 each formed an independent class, for a total of eleven classes.

[0158] (h-1) First Verification: Linear Discriminant Analysis (LDA) was used to verify the preliminary classification results of the above eleven categories. Based on these eleven classification labels, the results showed that the categories of samples JC1~JC3 and JC4~JC5 had significant overlap in the discriminant space, and the discriminant boundaries between categories were unclear. The verification results were inconsistent with the first preliminary classification results, indicating that the preliminary classification did not accurately reflect the actual source characteristics of the samples and that a new preliminary classification was required.

[0159] (g-2) Preliminary Classification (Second Time): Based on the verification results, the preliminary classification method was changed to hierarchical cluster analysis to reclassify the elemental composition data of samples JC1 to JC14. Preliminary classification results: Samples JC1 to JC5 clustered into one class; samples JC6 to JC14 each formed their own independent class, for a total of ten classes.

[0160] (h-2) Second verification and examination of group centroids: Linear discriminant analysis was used to analyze and verify the above ten categories of samples. The ten category labels were input, and a discriminant model was constructed. The results showed that each category of samples achieved "minimum intra-class difference and maximum inter-class difference" in the discriminant space. The verification results were completely consistent with the second preliminary classification results, indicating that the classification results had statistical discriminant validity and were accurate (e.g., Figure 29 (As shown). Among them, sample JC10 is classified as category 1, sample JC11 as category 2, sample JC12 as category 3, sample JC13 as category 4, sample JC14 as category 5, samples JC1~JC5 as category 6, sample JC6 as category 7, sample JC7 as category 8, sample JC8 as category 9, and sample JC9 as category 10.

[0161] The linear discriminant analysis results were imported into Origin plotting software and plotted as a two-dimensional spectrum. The identification results are as follows: Figure 30 , Figure 31 As shown. By Figure 30 , Figure 31 It is evident that the centroids of sample groups JC1 to JC5 coincide, and they cluster in the two-dimensional / three-dimensional spectra, proving that samples JC1 to JC5 share a common identity. Conversely, the centroids of the ten sample groups separate, and they are discrete in the two-dimensional / three-dimensional spectra, proving that these ten sample groups do not share a common identity. Specifically, samples JC1 to JC5, JC6, JC7, JC8, JC9, JC10, JC11, JC12, JC13, and JC14 do not share a common identity. Verification by the fire and rescue department confirms that these conclusions are consistent with the actual situation, and the identification method is accurate and effective.

[0162] Comparative Example 1

[0163] Energy dispersive spectroscopy (EDS) was used to scan and analyze two fallen welded iron pieces found on different floors in Example 3. Figure 32 As shown, when using energy dispersive spectroscopy (EDS) for analysis, both methods detected Fe and C, making it impossible to effectively distinguish their composition. This means that this method lacks the capability for tracing the origin of physical evidence.

[0164] Comparative Example 2

[0165] Energy dispersive spectroscopy (EDS) was used to scan and analyze the evidence samples JC1~JC4 in Example 7, such as... Figure 33 As shown. When using energy dispersive spectroscopy for analysis, Figure 33 (a) Figure 33 (b) Figure 33 (c) Figure 33 (d) All four pieces of evidence tested positive for Al, making it impossible to effectively compare the attribution of evidence JC401 with evidences JC1, JC2, and JC3. Similarly, when the samples were JC402, JC403, JC404, and JC405, only Al was detected. In other words, this method lacks the capability for tracing the origin of physical evidence.

[0166] Comparative Example 3

[0167] The samples from Example 4 were analyzed, wherein step S1(c) did not use dimethylchlorosilane, but only tetrahydrofuran soaking; the remaining steps were consistent with Example 4. The identification results were as follows: samples JC-1 and JC-2 belonged to one category, and samples JC-3 to JC-5 each belonged to a separate category, for a total of four categories; among them, samples JC-1 and JC-2 were identical, and the four categories of samples were not identical to each other, that is, samples JC-1 and JC-2, JC-3, JC-4, and JC-5 were not related as identical. Figure 34 As shown. After verification by the fire and rescue department, the above conclusion is inconsistent with the actual situation, and the assessment conclusion is incorrect.

[0168] Comparative Example 4

[0169] The samples from Example 5 were analyzed, wherein in step S1(c), a polar treatment agent was prepared by mixing dimethylchlorosilane (50%) and tetrahydrofuran (50%); the remaining steps were consistent with those of Example 5. The identification results were as follows: samples JC1 and JC3 belonged to one category, while samples JC2, JC4, and JC5 each belonged to a separate category, for a total of four categories. Among these, samples JC1 and JC3 shared a common identity, while the four categories of samples did not share a common identity with each other. Specifically, samples JC1 and JC3, and samples JC2, JC4, and JC5, did not share a common identity. Figure 35 As shown. After verification by the fire and rescue department, the above conclusion is inconsistent with the actual situation, and the assessment conclusion is incorrect.

[0170] Comparative Example 5

[0171] The samples from Example 6 were analyzed, with step S2(f) using all 25 elements from B, Mg, Si, P, Sc, V, Cr, Mn, Co, Ni, Ga, As, Sr, Mo, Pd, Cd, Sb, Ba, Ce, Ho, Pt, Au, Hg, Ti, and Pb, including elements with excessively high or low content; the remaining steps were consistent with Example 6. The identification results were: samples B2-2 and w2 belonged to one category, and the remaining samples each belonged to a separate category, for a total of five categories; among them, samples B2-2 and w2 were identical, and the five categories of samples were not identical to each other, i.e., samples B2-2 and w2, B1-1, B1-2, B2-1, and w1 were not identical to each other. Figure 36 As shown. After verification by the fire and rescue department, the above conclusion is inconsistent with the actual situation, and the assessment conclusion is incorrect.

[0172] Comparative Example 6

[0173] The samples from Example 7 were analyzed, where step S2(f) used eight elements from Si, V, Cr, Ga, Pd, Ce, Pt, and Au; the remaining steps were consistent with Example 7. The identification results were as follows: Samples JC1, JC3, JC402, JC403, and JC404 belonged to one category; samples JC401 and JC405 belonged to another category; and JC2 belonged to a third category, for a total of three categories. Among these, samples JC1, JC3, JC402, JC403, and JC404 were identical; samples JC401 and JC405 were identical; and the three categories of samples were not identical to each other. That is, samples JC1, JC3, JC402, JC403, and JC404, sample JC2, and samples JC401 and JC405 were not identical to each other. Figure 37 As shown. After verification by the fire and rescue department, the above conclusion is inconsistent with the actual situation, and the assessment conclusion is incorrect.

Claims

1. A method for tracing and identifying the identity of physical evidence in electrical fires, characterized in that, Includes the following: After removing external interferences from the surface of each sample, the samples are digested and their elemental composition is determined. Based on the elemental composition of each sample, a preliminary classification is performed using field investigation, principal component analysis, or hierarchical cluster analysis. The preliminary classification results are then verified using linear discriminant analysis, and the group centroids of each group are examined. When the preliminary classification results and the verification results are consistent, samples represented by groups with overlapping centroids are considered to be identical, while samples represented by groups with separate centroids are considered to be dissimilar. The exogenous interfering substances include non-polar and polar exogenous interfering substances. The sample to be tested is first immersed in a non-polar treatment agent to remove the non-polar exogenous interfering substances, and then immersed in a polar treatment agent to remove the polar exogenous interfering substances. The non-polar treatment agent is a solution of cyclohexane and toluene, and the polar treatment agent is a solution of dimethylchlorosilane and tetrahydrofuran.

2. The method for tracing the identity of electrical fire evidence according to claim 1, characterized in that, The non-polar treatment agent contains 50% to 80% cyclohexane and 20% to 50% toluene, with the sum of their volume percentages being 100%; the polar treatment agent contains 10% to 30% dimethylchlorosilane and 70% to 90% tetrahydrofuran, with the sum of their volume percentages being 100%; ultrasonic oscillation is performed during the soaking process.

3. The method for tracing the identity of electrical fire evidence according to claim 1, characterized in that, After removing the exogenous interfering substances from the sample surface, at least two sampling points at different locations of the same sample are selected for digestion in the digestion solution. After complete digestion, the sample is evaporated to dryness, deionized water is added to make up the volume, and the elemental composition of the sample is determined.

4. The method for tracing the identity of electrical fire evidence according to claim 3, characterized in that, Each sampling point contains 50mg to 100mg of solution, which includes hot nitric acid.

5. The method for tracing the identity of electrical fire evidence according to claim 1, characterized in that, The elemental composition of the sample was determined by inductively coupled plasma atomic absorption spectrometry. The sample elemental composition included several of the elements B, Mg, Si, P, Sc, V, Cr, Mn, Co, Ni, Ga, As, Sr, Mo, Pd, Cd, Sb, Ba, Ce, Ho, Pt, Au, Hg, Ti, and Pb.

6. The method for tracing the identity of electrical fire evidence according to claim 5, characterized in that, From the elemental composition of the sample, elements with excessively high or low content were removed, and 10 to 20 elements with similar content were selected for preliminary classification.

7. The method for tracing the identity of electrical fire evidence according to claim 1, characterized in that, When the preliminary classification results and the verification results are inconsistent, the preliminary classification is repeated until the final preliminary classification results and the verification results are completely consistent, and then the group centroids of each category are examined.

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