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What is ATPV, and how is it used in your hazard assessment?
Put simply, ATPV—Arc Thermal Performance Value—is the most commonly reported test result of the effectiveness of FR clothing. It measures the amount of incident energy that your FR garment can protect you from before the onset of a 2nd degree burn. And the FR garments in your safety program must meet or exceed the Incident Energy required based on your hazard assessment. But it’s a bit more complicated than that.
To better understand ATPV, let’s start with an overview of two main concepts: The Stoll Curve and Arc Ratings.
The Stoll Curve
The Stoll Curve is the predictive model used to measure the probability of burn injury. It quantifies the heat levels and exposure times that result in a second-degree burn, including high temperature exposure for a short time and low temperature exposure for a much longer duration.
An arc rating is the protection level afforded by an FR fabric when exposed to an electric arc. The arc rating of a fabric is determined by exposing the fabric to a staged electrical arc. In real life, arc behavior can be unpredictable, so the testing requires samples be exposed to a “controlled” arc utilizing the ASTM 1959 standard.
That brings us to ATPV (Arc Thermal Performance Value), which is a type of arc rating. The ATPV of an FR garment indicates that you have a 50% chance of the onset of a 2nd degree burn if exposed to an electric arc with the same calories of incident energy. The fabric will usually not break open unless exposed to incident energy levels higher than the arc rating.
So why is ATPV important? Think about it this way:
Let’s go back to what ATPV measures:
The amount of incident energy that your FR garment can protect you from before the onset of a 2nd degree burn.
Why is that important?
• By definition, second-degree burns cause a blistering, blisters can break the skin (that’s why the test is designed around 2nd degree burns).
•One of the pathways to infection is broken skin.
• One of the causes of death in burn victims is infection.
When you think about it that way, matching the ATPV of the FR garments in your safety program to the value required by your hazard assessment is not just a matter of meeting the standards. For your guys, it can be the only thing that stands between them and a potentially life-threatening burn hazard.
To learn more about ATPV and Arc Ratings, download our whitepaper: Understanding Arc Ratings
Arming your crew with the appropriate FR gear is a feat in itself. Navigating the ever-changing sea of standards? Now that’s another beast entirely. Bulwark is here to help you choose the right FR program by ensuring you have a thorough grasp on the standards and what they mean for you—and your crew.
When the National Fire Protection Association (NFPA) introduced the term “Arc-Rated” or “AR” in its 2012 revision to NFPA 70E, it was a bit of a head-scratcher. The question on every safety manager’s mind was: what’s the difference between FR and AR? According to Bulwark’s Technical Training Manager, Derek Sang, the most basic and important thing to know when it comes to FR and AR is that all arc-rated clothing is flame resistant, but not all flame resistant clothing is arc-rated.
For a piece of clothing to be considered flame resistant, the fabric used to make the garment must withstand ignition and/or rapidly self-extinguish in order to protect the wearer from the dangers of flash fire, arc flash, molten metals and other hazards. In the event of a flash fire or arc flash, the FR PPE worn must resist catching fire, melting, and continuing to burn after the initial flash to act as a barrier between the wearer and the hazard.
The fabric used to create arc-rated clothing is subject to additional tests, above and beyond fabric labeled simply “FR.” Primarily, it is exposed to a series of arc flashes to determine how much energy the fabric is able to block before it would likely cause the wearer to obtain a 2nd degree burn, 50% of the time. The result of this test, expressed in calories, is known as the Arc Thermal Performance Value (ATPV).
Current standards for arc flash protection, detailed by NFPA 70E, state that all PPE clothing must also be flame resistant to qualify for an arc rating. In other words: all AR clothing is FR, but not all FR clothing is AR. This is because, based on the results of the series of tests outlined above, equipment rated FR may not always provide the adequate level of protection for workers who are at risk of encountering arc flashes. These employees—general industry electricians (70E)— must wear the appropriate level of AR clothing for the hazard, in order to reduce their risk of serious injury or death caused by an arc flash.
Just like all of us here at Bulwark FR, Alice Stoll (1917–2014) was committed to taking FR to the highest degree.
That’s because Stoll’s research in the 1960’s led to the Stoll Curve, which is what FR experts use to determine what PPE is needed to reduce burn injuries.
You’re probably thinking, how did Stoll know at what conditions did things get too hot to handle? The answer: burn research. And it involved the forearms of sailors!
When she worked in the United States Navy Reserves, Stoll teamed up with another researcher named Maria Chianta to study the reaction of human skin to thermal energy/heat.
She conducted further research on the skin of pigs and rats—not sailors, thankfully.
The big takeaway from Stoll’s research was understanding the amount of heat or thermal energy that results in a 2nd degree burn on human skin. Alice Stoll’s contribution to FR apparel with this research is a crucial part of the thermal testing used to evaluate the ability of a fabric to protect against a variety of workplace hazards like flash fire, electric arc, molten metal splash and others. It’s also important to note that the Stoll Curve represents a relationship between time and energy. As we measure those relationships, we can determine Arc Thermal Performance Value (ATPV) ratings, and Breakopen Threshold Energy (EBT) ratings as well as predict the time to 2nd degree burn injury through FR fabrics.
Stoll received a number of awards including the Achievement Award of the Society of Women Engineers in 1969. The Bulwark team is proud to celebrate Alice Stoll, who had an important role in advancing FR technology.