Arc Week Season 3, Ep. 4: Who Wins in a Dog Fight? ATPV vs. EBT Explained

In Episode 3, we went behind the scenes at the arc flash testing lab, Kinectrics, to see great balls of fire, better known as arc flashes. There we demonstrated exactly what happens to flame resistant (FR) fabric when an arc flash takes place and covered how to determine the arc rating of a garment. But did you know there are two “species” of arc ratings? As we uncover the science behind arc flash hazards, Scott Margolin, your host, and Chairman of ASTM F1959, answers one of our most frequently asked questions, “Which arc rating is better – ATPV or EBT?”

Breaking News! ATPV and EBT are Equal

To better understand the two arc ratings, let’s first define them; ATPV stands for Arc Thermal Performance Value, and EBT stands for Energy to Breakopen Threshold. Both ATPV and EBT are evaluated under the same test, ASTM F1959, and the first one to be reached is the reported arc rating. While both values can be reported, only one arc rating is given to fabric. As Scott mentions in this episode, the only difference between the two is the way in which they fail the ASTM F1959 test.

• Arc Thermal Performance Value (ATPV): means that you have a 50% chance of being burned if exposed to an electric arc with the same number of calories of heat. The fabric will usually not break open unless exposed to energy levels higher than the arc rating. ATPV fabrics are stronger than they are insulative because the fabric will burn through before it gets a hole in it.
• Energy to Breakopen Threshold (EBT): means that the garment will break open if exposed to the same number of calories, but you will not be burned. EBT fabric is typically more insulative than it is strong because it doesn’t allow the fabric to burn through before it gets a hole in it. If an EBT value is determined and found to be equal to or below a determined ATPV value, then the EBT value is reported as the arc rating and will be noted as “Arc Rating (EBT)” on the garment label.

An expert’s opinion.

We asked Brian Sheils, who serves on the ASTM International Board of Directors, to shed light on the topic of ATPV vs. EBT. Brian shares, “it doesn’t matter if an arc rating is ATPV or EBT; neither one is better than the other.” It does not matter if a garment is rated 8 Cal ATPV or 8 Cal EBT; both provide the same amount of protection. All AR fabrics will breakopen if exposed to energy levels significantly higher than their arc rating. If an arc-rated fabric is exposed to energies higher than its breakopen value, the potential for direct skin exposure or non-FR inner layer ignition may result in additional injuries.

The key takeaway.

A worker exposed to a potential arc flash hazard must understand the arc incident energy level possible and the protection level of the PPE they are wearing (the arc rating). From there, they must match the two so that the PPE they’re wearing meets or exceeds the incident energy level of the potential hazard, ensuring they are not burned. For example:

Please join us tomorrow to catch Episode 5: Shooting Down the Myth of “Deenergized Work.” Scott is joined by industry experts to discuss the “fuelishness” of workers who think they work deenergized, why they are at a greater risk of injury, and how to shoot down the myth by always wearing the proper PPE for the potential hazard.

Do you have a flash fire – rather than an arc flash – hazard? The hazards may differ, but the valuable lessons in this series are relevant to workers in oil and gas and other industries that use PPE to protect workers from thermal hazards. Tune in!