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Arc is a gas discharge phenomenon that presents arc-shaped white light and generates high temperature. The huge heat released by the arc can directly burn the skin or ignite clothing. At the same time, the high temperature will cause the explosive expansion of gases and metals in the environment, and its speed is enough to penetrate into the human body. Huge damage to the human body. In the daily work of electric power workers, except for heat sources such as arc welding and electric arc furnaces, most of the arc phenomena are detrimental to personal safety and equipment safety. At present, there are two standards for judging the arc protection level, namely arc thermal protection performance (atpv value) and material rupture threshold energy (ebt value), whichever is smaller is used as the arc protection performance of flame retardant protective clothing.

 

In 2011, China's power industry promulgated the "General Technical Requirements for Personal Arc Protection Equipment" (DL-T 320-2010), which added a new standard to the field of personal protective textiles in China.

 

A common problem in the field of anti-arc fabrics and clothing is: whether the arc level ATPV value or the arc level EBT value can better reflect the protective performance of clothing. As a standard related to human life, any wrong concept may lead to fatal injury. The United States has decades of protection experience in the field of arc protection. For this reason, the author would like to make some brief introduction and analysis of the ATPV value and EBT value with reference to the relevant standards of the American Standard and foreign language materials.

 

While ASTM F1959, a method for testing the arc rating of clothing materials, was still in development, committee ASTM F18 (the American Society for Experimental Materials Workers Committee on Electrical Protective Equipment) recognized that some materials could give the skin an early warning of a burn before the material ruptured, while Other materials cannot. As a result, two rating criteria were initially created: one is ATPV, the arc thermal property value; the other is EBT, the material rupture threshold energy value.

 

One company made a distinction between the two in the early stages of their market, citing the absence of "bursts" in the materials they tested. This conclusion is arbitrary, as subsequent experiments have shown that each type of fiber ruptures before it reaches the predicted level of combustion. Now, we find that knitted fabrics generally break before the burn point and woven fabrics burn before the break point, and each fabric structure and type of fiber has its own advantages and disadvantages.

 

The committee re-named the arc rating for two reasons: first, to simplify the terminology on the label for better understanding by end users, and second, to eliminate misconceptions about EBT. In many respects, the committee has retained the EBT and ATPV values ​​as a note or appendix in the arc rating, which is of great significance for the more professional and safe use of arc protective clothing. So now we can see that the arc protection suits are marked with ATPV = X cal/cm2 or EBT = X cal/cm2.

 

Fabrics marked with EBT values ​​did not show second-degree burns on the calorimetric sensor in most cases because the tiny cracks in the fabric were not directly on the sensor. In theory, if these cracks and holes are directly on the sensor, there will be a burn prediction in the cracks and holes, so it can be rated directly. Both arc levels are in cal/cm2 and the minimum value is usually recorded. That is to say, both the EBT value or the ATPV value can be recorded, but only one is finally selected as the arc rating of the fabric. According to ASTM F1506 (Standard Performance Specification for Textile Materials Used in Protective Clothing for Electrical Workers Exposed to Instantaneous Arcs and Related Thermal Hazards) regarding arc ratings, only minimum values ​​may be written on clothing labels.

 

To assess the arc rating of clothing according to the ASTM F1506 standard, the fabric has to go through multiple tests, such as the fabric must pass the water wash test and the ASTM D6413 vertical burn test. That is, for a fabric to be truly flame retardant under arc, flash, or any flame conditions, it must meet a series or more comprehensive tests.

 

The two metrics that define the arc rating according to the ASTM standard are as follows:

 

The ATPV value is based on the Stoll curve, and the energy incident on the material has a 50% chance of causing enough heat to penetrate the specimen to cause a second degree burn.

 

The EBT value is the energy incident on the material that has a 50% probability of breaking the sample. When the total area of ​​holes in the fabric exceeds 1.6cm2, we consider it to be broken.

 

Both ATPV and EBT are rated using the same test method (ASTM F1959), but the arc rating is recorded using the value achieved first. If the thermal insulation value of the material is greater than the arc tensile strength, the material will break first; otherwise, it will burn before it breaks.

 

If the EBT value is equal to or less than the ATPV value, then "EBT" will be taken as the arc rating value and marked as the arc rating (EBT); if the EBT value is greater than the ATPV value, then "ATPV" will be taken as the arc rating value and marked as the arc rating .

 

We can also understand these levels from another angle:

 

ATPV: In an 8-card flame retardant arc-proof fabric test, the probability of causing a second degree burn is 50%; EBT: In an 8-card flame-retardant arc-proof fabric test, the possibility of forming a 2.54cm crack on the material is 50%.

 

In practical applications, we cannot use the ATPV value or EBT value to judge the protective performance of clothing, because they are "functionally equivalent", and there is no difference between the two ratings. Basically fabrics labeled "EBT" are generally more insulating than they are strong, while fabrics labeled "ATPV" are the opposite. If there is a difference, then the fabric marked "EBT" usually means that the garment is a knitted fabric, which is more comfortable to wear, but there is no essential difference in the protection of the wearer between the two.