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ATPV

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ATPV means Arc Thermal Protective Value. This value is measured in calories per square centimeter and represents the maximum performance capability for arc-flash protection of a particular garment or fabric.

When flame resistant clothing or fabric is tested via test method ASTM 1959, two things can occur: the garment or fabric will break open, or it will remain intact while surpassing the heat threshold for a 50% probability of a 2nd degree burn, based on the Stoll curve. Once the heat threshold of a garment is surpassed, it is is no longer protective from burn injury, regardless of its arc rating. Therefore, the arc rating, or ATPV, is typically recorded 'at' the heat threshold.

Translation - an FR shirt might be able to protect you from the incident energy of a 40 cal arc event. In this same shirt, the heat from a smaller 8 cal event might give you 2nd degree burns. Let's rate the shirt to 8 cal, no? The ATPV rating accounts for both the incident energy and heat transfer.

Most woven fabrics (think twills, shirt, pant or coverall material) will not break open, and thus will be assigned an ATPV value.

See also EBT.
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Slate Rock Safety LLC, Safety Equipment & Clothing, Medina, OH