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There are double standards for determining the function of arc protection clothing

2020-10-22 11:15 | writer: admin

The general question in the field of arc-proof clothing is: whether the arc level ATPV value or the arc level EBT value can better reflect the protective performance of the clothing. As a standard related to human life, any misconception may lead to fatal injuries.
 When ASTMF1959, the method for testing the arc level of clothing materials, was still in the development stage, the ASTMF18 committee (American Society for Experimental Materials Workers’ Electrical Protection Equipment Committee) recognized that some materials can make the skin feel the burning warning before the material ruptures, while other materials You can't. Therefore, two grading standards were produced at the beginning: one is ATPV, arc thermal performance value; the other is EBT, material rupture threshold energy value. Experiments have shown that every fiber will break before reaching the predicted level of combustion. Now, we find that knitted fabrics usually break before the burning point and woven fabrics burn before the breaking point. Each fabric structure and each type of fiber has its own advantages and disadvantages.
The committee renamed the arc level for two reasons: one is to simplify the terminology on the label so that the end user can better understand it, and the other is to eliminate the misunderstanding of EBT. From many considerations, the committee retained the EBT and ATPV values ​​as a mark or appendix in the arc level, which is of great significance for the more professional and safe use of arc-proof clothing. So now we can see that ATPV=Xcal/cm2 or EBT=Xcal/cm2 is marked on the label of arc protection clothing.
In most cases, the fabric marked with the EBT value does not show a second degree burn on the calorimetric sensor, because the tiny cracks in the fabric are not directly on the sensor. In theory, if these crack holes are directly located on the sensor, there will be a burn prediction at the place of the crack hole, so it can be directly rated. Both arc levels are in cal/cm2, and the smaller value is usually recorded. In other words, EBT value or ATPV value can be recorded, but in the end only one is selected as the arc rating of the fabric. According to ASTMF1506 (standard performance specification for textile materials used in protective clothing worn by electrical workers exposed to instantaneous arcs and related thermal hazards), only the smaller value can be written on the clothing label.
If the arc rating of clothing is assessed according to ASTMF1506 standard, the fabric has to go through multiple tests, such as washing test and ASTMD6413 vertical burning test. In other words, for fabrics to truly achieve flame resistance under arc, flash fire or any flame conditions, they must meet a series of or more comprehensive tests.
According to ASTM standards, the two indicators of arc level are as follows:
The ATPV value is based on the Stoll curve. The energy incident on the material has a 50% probability that enough heat can penetrate the specimen to cause a second degree burn.
The EBT value is that the energy incident on the material has a 50% probability of breaking the sample. When the total area of ​​holes in the fabric exceeds 1.6cm2, we regard them as broken.
Both ATPV and EBT are evaluated by the same test method (ASTMF1959), but the first reached value is used to record the arc level. If the material's thermal insulation value is greater than the arc tensile strength, the material will rupture first; otherwise, it will burn before it ruptures.
If the EBT value is equal to or less than the ATPV value, then "EBT" will be regarded as the arc level value and marked as the arc level (EBT); if the EBT value is greater than the ATPV value, then "ATPV" will be regarded as the arc level value and marked as the arc level .
We can also use another angle to understand these levels:
ATPV: In an 8-calorie test, the probability of causing a second degree burn is 50%; EBT: In an 8-calorie test, the probability of a 2.54cm crack on the material is 50%.
In practical applications, we cannot use ATPV or EBT to judge the protective performance of clothing because they are "functionally equivalent" and there is no difference between the two ratings. Basically, the insulation of the fabric marked "EBT" is usually greater than its strength, while the fabric marked "ATPV" is the opposite. If there is a difference, then the fabric marked "EBT" usually means that the garment is knitted and has better wearing comfort, but there is no essential difference between the two in protecting the wearer.

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