Which Type of Arc Rating Best Measures Protection?

This is the third post in a six-part “Fundamentals of Arc Flash” series. Check back regularly to read new posts offering valuable information on topics such as arc flash causes and characteristics, ratings, and analysis.

The evidence is clear, arc-rated flame resistant (FR) clothing saves lives! In the event of an arc flash, arc-rated garments do not ignite, and they insulate you against the hazard so that you’re not burned through the fabric. ASTM F1959, Standard Test Method for Determining the Arc Rating of Materials for Clothing, is the official method for determining how much heat from an arc flash a certain fabric (or system of fabrics) will block before the onset of second degree burns to the wearer. There are two ways to achieve an arc rating:  Arc Thermal Performance Value (ATPV) and Energy to Breakopen Threshold (EBT). But what is the difference between the two, and is one better or more protective?

The short answer is: while they’re slightly different, they’re also the same.

Learn more in this short video featuring Scott Margolin, Vice President of Technical at Tyndale and recognized Subject Matter Expert:

As Scott notes, the difference between the two ratings is that when incident energy exceeds a fabric’s arc rating, an ATPV fabric is likely to remain intact, but may allow some 2nd degree burn, while an EBT fabric will likely develop a hole, but probably will not allow 2nd degree burns through the fabric.  This is generally true for incident energies a few calories above arc ratings.  Almost all arc rated fabrics will break open and/or allow 2nd degree burns with higher incident energy.  But, as Scott explains, an ATPV fabric is more resilient than it is protective, and an EBT fabric is more protective than it is resilient.

The important thing to know is that both ATPV and EBT ratings protect the wearer from burn injury when the arc rating is greater than the arc incident energy; they are equally protective. 

So, the key is to wear clothing with an arc rating greater than the incident energy that can potentially be generated by the task at hand!

What happens if actual incident energy exceeds the arc rating of the garment you’re wearing? While you should never knowingly wear garments whose arc rating is lower than the predicted arc incident energy, arc ratings are, by design, fairly conservative. As a result, wearers can sometimes escape injury when the incident energy exceeds the arc rating by a few calories.

Want to learn more? Check out our past post for more information about ATPV and EBT arc ratings. You can also browse our archives to learn more about arc flash protection, and stay tuned for more posts in our Fundamentals of Arc Flash series.

Need some new arc-rated clothing to stay safe on the job? Shop with us today at www.TyndaleUSA.com or give us a call at 800-356-3433.




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