GB 16840.3-1997 Technical identification methods for electrical fire causes Part 3: Component analysis method
Some standard content:
GB 16840.3--1997
The series of standards of "Technical identification methods for electrical fire causes" consists of 4 parts: Part 1 Macroscopic method; Part 2 Residual magnetism method; Part 3 Composition analysis method; Part 4 Metallographic method. This standard is Part 3 of the series of standards of "Technical identification methods for electrical fire causes": Composition analysis method.
Composition analysis method is a method to identify the cause of fire according to the different elements contained in the cavities of short-circuit molten beads of steel wires at the fire scene, and thus according to the different contents of various elements. This standard consults and refers to papers and materials such as "Analysis of the composition of the outer surface of short-circuit melt marks" in Switzerland, "Study on the discharge ignition phenomenon of the wire core to the insulation layer" in Japan, and "Identification of primary and secondary short-circuit melt marks". This standard is proposed by the National Fire Protection Standardization Technical Committee. This standard is under the jurisdiction of the Sixth Subcommittee of the National Fire Protection Standardization Technical Committee. The drafting unit of this standard: Shenyang Fire Science Research Institute of the Ministry of Public Security. The main drafters of this standard: Wang Xiqing, Han Baoyu, Di Man, Gao Wei. 73Www.bzxZ.net
1 Scope
National Standard of the People's Republic of China
Technical determination methods for electrical fire causePart 3: Component analytic methodGB 16840.3-1997
This standard specifies the definition, principle, equipment, method steps, determination and written procedures to be followed during inspection and identification. This standard is applicable to the investigation of the cause of electrical fire, and the identification of the relationship between the melting cause and the cause of the fire from the characteristics of the different elemental components contained in the inner surface of the short-circuit molten bead cavity on the copper conductor. That is, whether it is a primary short-circuit molten bead or a secondary short-circuit molten bead. 2 Definitions
This standard adopts the following definitions:
2.1 Melted mark caused by short circuit A round bead-shaped melting mark formed at the end of a copper-aluminum conductor under the high temperature of a short-circuit arc. 2.2 Primary short circuit melted mark Primary short circuit melted mark The short circuit melted mark formed by the copper-aluminum conductor due to its own fault before the fire. 2.3 Secondary short circuit melted mark The mark left after the copper-aluminum conductor is charged and the insulation layer fails under the action of external flame or high temperature. 2.4 Inside carity caused by short circuit melted mark All melted beads formed at the end of the wire due to short circuit have a cavity inside, and the inner surface of the cavity has the characteristics of the environmental conditions when the short circuit is formed. 3 Principle
The mechanism of the formation of the cavity inside the short circuit melted bead is complex, but it is mainly because the oxygen absorbed by the metal during melting has not had time to fully react with the metal or escape, and is trapped in the internal organization to form a cavity. Due to the different environmental conditions for the formation of the primary short circuit melted bead and the secondary short circuit melted bead, the different environmental conditions will inevitably enter the molten metal at the moment of the wire melting, so that some characteristics of different short circuit environmental conditions are retained on the inner surface of the short circuit melted bead cavity. 4 Equipment and instruments
4.1 Auger electron spectrometer (scanning imaging). Other types of spectrometers can also be used. The specific components, equipment and operation of the Auger electron spectrometer should be carried out in accordance with the provisions of the instrument manual; when observing the sample, choose according to the required magnification.
4.2 Analysis conditions
Analysis conditions include
Analysis chamber vacuum: less than 7×10-7Pa;
Primary electron energy: 3keV,
Approved by the State Bureau of Technical Supervision on June 3, 1997, 74
Implementation on May 1, 1998
Primary electron beam current: 0.5uA;
Primary electron beam diameter: <2μm,
GB16840.3—1997
Before starting up, make sure that the power supply voltage is stable at 220V; Before connecting the electrical cabinet to the power supply, the filament current and voltage knobs should be set to zero; The control mode of the filament current should be set to It. The maximum current is close to 2.6A (the knob reading is 5.2); - When measuring the elastic peak, Ep≤2000eV, and the multiplier high voltage is 1kV; when measuring the Auger signal, Ep can be 3keV, 5keV, or 10keV, and the multiplier high voltage is 1.5kV or more. In the pulse counting mode, the multiplier high voltage can be up to 2.5kV;
The sensitivity of the lock-in amplifier should be adjusted from low to high, and it should be set to the lowest gear (250mV) before switching the power supply. 5 Methods and Steps
5.1 Sample Extraction
5.1.1 Sample Processing
During the entire sample processing process, it is necessary to ensure that the original state of the sample is not damaged and no contamination is introduced to avoid interfering with the test results; when extracting the short-circuit molten bead, remember not to touch it directly with your hands, but to hold it with tweezers, clamp the selected molten bead with pliers on the rod, and use another pair of pliers to split the molten bead. The clamping parts of the pliers used should be cleaned with acetone and alcohol in advance. Do not contact other substances that can introduce pollution and interfere with the analysis results;
Before opening the bead, if the surface of the bead is contaminated, clean it thoroughly with acetone and alcohol, and then open the bead after the solvent is dry; in order to keep the information of the current environmental atmosphere carried by the short-circuit bead from being destroyed, do not soak it with solvent, especially the opened bead, to avoid contamination of the cavity, and shorten the time it stays in the air as much as possible. The temporarily unused bead can be placed in a clean container. 5.1.2 Inspection of sample composition
Use clean pliers to separate the joint between the molten bead and the rod, and use conductive glue to stick the opened molten bead to the sample holder. When sticking the sample, the hollow of the molten bead should face upwards, and the cross section of the molten bead should be as parallel to the plane of the sample holder as possible; when sticking the sample with conductive glue, stick it firmly, and do not use too much conductive glue. Remember not to let the conductive glue immerse the cross section of the molten bead. It is best to squeeze several molten beads together and stick more for easy selection during analysis; after the sample is stuck and the conductive glue is dry (about 10 minutes), put the sample into the system for During analysis, the process from spotting the molten bead to loading it into the instrument should be as fast as possible, and the time it stays in the air should be minimized; the sample should not be cleaned with Ar+ ion beam before analysis to ensure that the environmental condition characteristics retained on the inner surface of the cavity during the short circuit are not destroyed; during analysis, electron beam scanning imaging is used to determine the position of the inner surface of the cavity to be analyzed, and the magnification is generally 100 to 200 times; after selecting the analysis point, fixed-point analysis can be carried out, but it should be noted that the depth of the cavity is different, and the distance between the analysis point and the analyzer should be adjusted in time during analysis to ensure a large enough signal. 5.1.3 Notes on sample analysis
—Some cavities in a molten bead are too deep to receive a sufficiently large signal; the cavities in a molten bead are very small, with most cavities less than 1 mm in diameter. The components on the inner surface of the cavity are mainly C, N, O, etc., which are all ultra-light elements. The surface aggregation is very thin, with a thickness of only an atom. Commonly used electron microscopes, electron probes, scanning electron microscopes, and X-ray spectrometers are unable to complete such analysis. Only scanning Auger electron spectrometers can meet these special requirements; the cavities in the molten bead are small, and it is difficult for all Auger electrons generated in the cavities to be ejected. Only a small number of Auger electrons are received, and the final signal is very small, or even no Auger signal can be received. In an Auger spectrometer using a simple mirror analyzer, the position of the cavity to be analyzed must be adjusted at any time to ensure that the analysis point is at the optimal working point of the analyzer to obtain the largest possible Auger signal; in order to ensure reliable results and reduce statistical errors, as many cavities as possible should be analyzed in a limited sample. 6 Determination
6.1 Element content on the inner surface of primary and secondary short-circuit molten beads of conductors 75
GB16840.3—1997
The inner surface of the cavity of the short-circuit molten beads of conductors contains S, Cl, C, N, O, Cu and other elements. The amount of different elements contained in the inner surface of the cavity of the short-circuit molten beads formed under different environmental conditions is also different. The average values of the contents of different elements measured in a large number of samples are shown in the following table for determination. The most representative elements are C and N. Because in the combustion atmosphere, C and N elements come from the atmosphere. 6.1.1 Weight percentage
—First melt mark
Second melt mark
Inner surface of cavity
Inner surface of cavity
Atomic concentration percentage
Second melt mark
Second melt mark
Inner surface of cavity
Inner surface of cavity
Written procedures to be followed during inspection and appraisalCl
7.1 When submitting for inspection, the unit submitting the inspection shall first fill out the application form for technical identification of the cause of electrical fire, which shall include the name, address, contact person of the unit applying for the identification, the name of the unit on fire, the name and quantity of the sample, the sampling location, the sampler, and the purpose of the identification. 7.2 After accepting the identification task, the identification unit shall fill out the sample receipt form, task form, reception record, and original record. 7.3 After the identification is completed, the identification conclusion shall be filled in the identification report approval form, signed by the person in charge of the laboratory, and submitted to the leader for approval after the quality review is correct.
7.4 The original of the approved identification report shall be submitted to the unit submitting the inspection, and a copy shall be kept for record. 76
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