ATPV Vs EBT Arc Ratings

In the past some have asked the difference between ATPV (Arc Thermal Protection Value) and EBT (Energy Breakopen Threshold). So in this article we aim to highlight and explain the differences between ATPV or EBT.

Calorific Values

The important thing to be considered is the cal/cm2 which the fabric can support. In the US the requirements are summarised as followed:

  • Category I > 4 cal/cm2
  • Category 2 > 8 cal/cm2
  • Category 3 > 25 cal/cm2
  • Category 4 > 40 cal/cm2

What you need to know.

In the development stages of the ASTM F1959 Standard Test Method (which was used to determine the Arc Rating of Materials for Clothing) it was quickly recognised that some materials would allow skin burn prediction to be reached before they “broke open” and others would not. Initially these had become two ratings – the first was an ATPV, an arc thermal performance value and then the other was an EBT, an energy breakopen threshold. The reason why one of these ratings was marketed better than the other was because the materials they had tested did not exhibit the “breakopen” phenomena.

This way of thinking was a mistake and later it was determined that every fiber type can breakopen before its burn prediction level is reached. Today we recognise that knits usually breakopen before the point of burning and woven cloth shows signs of burning before the breakopen point. In fact all fibers have their disadvantages and advantages. It was therefore decided that the term would be renamed to “Arc Rating”. The main reason for arc rating was so that labeling would be less technical and easier for the user to understand. Additionally it was to remove false stigma associated with EBT. The arc rating term was announced back in 2000 but it took several years for it to be fully adopted. Due to this it was decided to leave the term EBT and ATPV as a subscript or an addendum to the term Arc Rating. This means that today you will see a label with Arc Rating (ATPV) = X cal/cm² or Arc Rating (EBT) = X cal/cm². In case you do not understand what the label is telling you, both are a fifty percent probability of the behavior at which the material can give a second degree burn. The Arc Rating (EBT) fabric has not exhibited a second degree burn on the calorimeter sensors in the majority of cases because the material has a one inch crack or a ½ square inch hole which is not directly over the sensor.

Each material receives an EBT or an ATPV. Although both of these values can be reported only one of these is the Arc Rating for the fabric. According to the ASTM F1506 specification, it is only the lowest which can be used on the clothing label. In order for a piece of clothing to be arc rated in the ASTM F1506 standard, the fabric has to undergo several tests which it must pass including wash testing and vertical flammability testing using ASTM D6413 which is a small scale test. To be really flame resistant for arc flash, flash fire or any real fire conditions, the fabric must pass a battery of tests and/or a full scale test.

An additional way to look at these ratings is as follows:

Arc Rating can be of two types.

1. ATPV: This is 50% probability of second degree burn in the 8kA arc test on a flat panel.

2. EBT: This is the 50% probability of a one inch crack in the material in the 8kA arc test on a flat panel.

So the conclusion from this is that neither is better. EBT fabrics are generally more insulative than they are strong and ATPV materials are stronger than they are insulative. Usually EBT would indicate that the garment is a knit and more comfortable but essentially no less protective to the user. This means that in the future never make a clothing protection decision based on the fact that the clothing received an ATPV or an EBT as They are “functional equivalents”.