Source: kckate16 (Envato Elements)
The arc rating of a material is a measure of how well it can protect the wearer from burns resulting from arc flashes.
Sounds simple enough. But it gets a bit more complicated, because there are actually two types of arc rating.
Depending on the arc flash PPE you’re looking at, it might have an Arc Rating (ATPV) or an Arc Rating (EBT). They both indicate how well the PPE will protect the user, but they each measure something different.
So, let’s take a moment to review the the difference between ATPV and EBT and what it means for your arc flash protection.
Arc Thermal Performance Value (ATPV)
ATPV stands for Arc Thermal Performance Value. As the name implies, it’s a measure of how much thermal protection the material will provide.
Specifically, it indicates how much heat energy (measured in calories) it would take for the user to have a 50% chance of sustaining a second degree burn through the material.
The higher the ATPV, the higher the protection it affords.
Energy Break-Open Threshold (EBT)
EBT stands for Energy Break-Open Threshold. Unlike the ATPV, it doesn’t measure how much energy it takes for an arc flash to cause a second degree burn. Rather, it indicates how much heat the material can withstand before tearing or cracking.
To be precise, the EBT value represents how much incident energy it takes for the material to have a 50% chance of a break open. In the case of EBT, breaking open is defined as a hole in the material that is at least 0.5 square inches.
Like the ATPV, a higher EBT indicates a higher level of protection.
Why Are There Two Types of Arc Rating?
Having two types of arc rating can be a bit confusing, but there’s a simple rationale behind it.
Different types of material will put users at risk in different ways.
If arc flash PPE is made of a material that is likely to break open during an arc flash incident, the holes and cracks formed in the PPE will leave the user exposed and unprotected.
Other materials might not break ope
n during an arc flash, but that doesn’t mean the user is safe. They can still suffer from serious burns despite wearing their PPE.
The two types of arc rating reflect these different scenarios – EBT for break opens that result in a burn and ATPV for burns that happen even when a break open doesn’t.
When arc rated PPE only displays the EBT value, that’s because a break open scenario is likely to occur before a burn. When it only displays the ATPV, that’s because a burn is likely to happen before the material breaks open.
In fact, arc rated PPE is typically tested for both. But in many cases, only the lower value gets printed. That’s because it doesn’t really matter how the material fails (whether due to burns or break opens) – all that matters is how much heat energy it can take before it does.
Which One Matters More?
Both values are considered equivalent. An arc rating (ATPV) of 25 cal/cm² provides the same protection as an arc rating (EBT) of 25 cal/cm².
You’ll typically see the ATPV rating on woven fabrics, because those tend to fail before breaking open. And you’ll usually see EBT on knit fabrics, because those tend to break open more readily.
But for practical purposes, that doesn’t really matter. All you need to know is that the arc rating of your PPE is suitable for the hazards you’ll be facing.
ATPV and EBT in a Nutshell
ATPV and EBT are both:
- Types of arc rating
- Measurements of the thermal protection offered by a material
- Indicators of how much heat energy the PPE can withstand before failing (50% of the time)
- Equivalent in value
But the key difference between them is that:
- ATPV measures the insulating properties of an arc rated material
- EBT measures the strength of an arc rated material
Ready to learn more? Check out our free webinar on How to Build an Arc Flash PPE Program Your Workers Will Embrace!
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