GB/T 16840.2-2021 PDF English (GB 16840.2-1997: Older version)
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| GB/T 16840.2-2021 | English | 110 |
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Technical determination methods for electrical fire evidence - Part 2: Residual magnetism method
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| GB 16840.2-1997 | English | 175 |
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[GB/T 16840.2-1997] Technical determination method for electrical fire cause. Part 2: Recidual magnetic method
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GB/T 16840.2-2021: PDF in English (GBT 16840.2-2021) GB/T 16840.2-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 13.220.20
CCS C 80/89
GB/T 16840.2-2021
Replacing GB/T 16840.2-1997
Technical determination methods for electrical fire evidence
- Part 2.Residual magnetism method
ISSUED ON. AUGUST 20, 2021
IMPLEMENTED ON. AUGUST 20, 2021
Issued by. State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword... 3
Introduction... 5
1 Scope... 6
2 Normative references... 6
3 Terms and definitions... 6
4 Principle... 7
5 Instruments, equipment and reagents... 7
5.1 Instruments... 7
5.2 Equipment... 7
5.3 Reagents... 7
6 Test materials... 7
6.1 Types of test materials... 7
6.2 Selection of test materials... 8
7 Methods and steps... 8
7.1 Preparation... 8
7.2 Measurement operation... 8
8 Determination criteria... 9
8.1 Data determination... 9
8.2 Comparative determination... 9
8.3 Determination of magnetization law... 10
Technical determination methods for electrical fire evidence
- Part 2.Residual magnetism method
1 Scope
This document specifies the principle, instruments, equipment and materials, test
materials, methods and steps, and determination criteria of the residual magnetism
method in the technical determination methods for electrical fire evidence.
This document applies to fire accident investigations, when no short circuit melted
marks or lightning melted marks are found at the scene of a building fire, the residual
magnetic data obtained from the testing of ferromagnetic metal conductors is used to
determine whether a large current short circuit or lightning strike has occurred.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 16840.1 Technical determination method for electrical fire evidence - Part 1.
Macroscopic method
3 Terms and definitions
For the purpose of this document, the terms and definitions defined in GB/T 16840.1
and the following apply.
3.1
residual magnetism
Magnetism retained by a ferromagnet after it is magnetized by the magnetic field
formed by the short-circuit current of a wire or the lightning current.
3.2
melted mark induced by lightning
Melted mark formed by the high temperature of the lightning current on a metal.
6.1.5 Equipment components and other magnetic metal materials, preferably small in
size.
6.2 Selection of test materials
6.2.1 Technical requirements for selection of test materials
6.2.1.1 Test materials shall be selected from representative parts.
6.2.1.2 The distance between the test material and the wire should be less than or equal
to 20 mm.
6.2.1.3 For sites where lightning strikes may occur, testing shall be carried out
according to actual conditions, without being restricted by the part.
6.2.1.4 Before testing, the location, state and morphological characteristics of the test
material shall be recorded by taking photos.
6.2.2 Precautions
6.2.2.1 Test materials fixed to walls or other objects shall not be bent, knocked or
dropped during extraction.
6.2.2.2 Test materials that are less affected by the temperature of the fire scene should
be tested.
6.2.2.3 Test materials located near magnetic materials shall not be tested.
6.2.2.4 If it is confirmed that a short circuit has occurred in the line near where the test
material is extracted, testing shall not be carried out.
7 Methods and steps
7.1 Preparation
7.1.1 Use cleaning reagent to clean the surface of the test material before measurement.
7.1.2 Clear the testing equipment to zero before measurement.
7.2 Measurement operation
7.2.1 Select measurement points according to the test material. For example, measure
two ends of iron nails, iron pipes, steel bars, etc.; measure corners of iron plates;
measure edges and corners of stray iron parts.
7.2.2 Place the probe (Hall element) flat on the test material, slowly change the position
and angle of the probe to perform search measurement until the maximum value when
the measurement data is stable.
7.2.3 The probe can be in contact with the test material, and no force shall be pressed.
8 Determination criteria
8.1 Data determination
8.1.1 When the test material is iron nails and iron wires, etc.
8.1.1.1 If the measured residual magnetic data is less than 0.5 mT, it is not used as a
criterion for the occurrence of short circuit or lightning strike.
8.1.1.2 If the measured residual magnetic data is greater than 0.5 mT and less than 1.0
mT, it is used as a reference for determining whether a short circuit or lightning strike
has occurred.
8.1.1.3 If the measured residual magnetic data is greater than 1.0 mT, it is used as a
criterion for the occurrence of short circuit or lightning strike.
8.1.2 When the test material is iron pipes and steel bars, etc.
8.1.2.1 If the measured residual magnetic data is less than 1.0 mT, it is not used as a
criterion for the occurrence of short circuit or lightning strike.
8.1.2.2 If the measured residual magnetic data is greater than 1.0 mT and less than 1.5
mT, it is used as a reference for determining whether a short circuit or lightning strike
has occurred.
8.1.2.3 If the measured residual magnetic data is greater than 1.5 mT, it is used as a
criterion for the occurrence of short circuit or lightning strike.
8.1.3 When the test material is stray iron pieces
8.1.3.1 Stray iron pieces include iron bars, angle irons, magnetic metals, etc. near the
wire.
8.1.3.2 If the measured residual magnetic data is greater than 1.0 mT, it is used as a
criterion for the occurrence of short circuit or lightning strike.
8.2 Comparative determination
When electrical lines pass through the same facilities at different locations on site,
measure the residual magnetic data of metal components on the facilities near the lines.
By measuring the size of the residual magnetic data, determine whether the wire passing
through the facilities with residual magnetic data has ever experienced a short circuit or
lightning strike.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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