ATPV And EBT Ratings For Arc Rated Clothing
Why is it that some FR clothing is rating with an ATPV (Arc Thermal Performance Value) and some arc rated clothing is rated with an EBT (Energy Breakopen Threshold) rating?
The answer is as follows:
An Arc Thermal Performance Value (ATPV) is defined as the arc incident energy required to cause the onset of second-degree burn. The higher the ATPV the more protective the fabric. This means that a person has a 50% chance of being burned if exposed to an electric arc with the same number of calories of heat as what the protective garment is rated for. The fabric will usually not break open unless exposed to energy levels higher than the arc rating which is why the rating assigned to the garment label is lower that the level (ATPV Rating) at which the fabric will fail.
An EBT rating comes into use when a garment has more of an insulation factor such as in an FR parka then the strength of the outer fabric as in a shirt. This is basically a comparison between the different garment designs and provides a method for determining the protective value. Basically whichever breaks open first be it the insulation that is built into the fabric or the outer fabric layer is how the rating is assigned to the garment as either ATPV or EBT. If the EBT rating is set at a higher value then the ATPV rating then the EBT is used and the ATPV rating would be used if it is higher. Important factors include fabric’s weight, construction fiber make-up and how it is all assembled in the finished product contribute to the rating.
It really doesn’t matter which rating is used when it comes to protection for the user in the sense of which one provides more protection. The bottom line is that the heat and arc exposure must be blocked and this is done by the fabric/insulation consuming the heat energy of the fuel source.
Terry Smeader
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