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ATPV / Ebt

The Arc Thermal Performance Value (ATPV) is the incident energy that results in a 50% probability that sufficient heat transfer through a material is predicted to cause the onset of second-degree burn injury. The Energy Break-Open Threshold (Ebt) is the incident energy that results in a 50% probability of material break-open.

Arc Thermal Performance Value (ATPV) And Energy Break-Open Threshold (Ebt)

 

ATPV Explained

The Arc Thermal Performance Value (ATPV) as defined by ASTM, is a measurement of how much heat energy a material can withstand before it allows enough heat to penetrate to cause a 50% probability of a second-degree burn, based on the Stoll Curve. The ATPV is a crucial factor in determining the level of protection needed by flame-resistant (FR) clothing when working around electrical hazards. The higher the ATPV rating, the greater the protection offered against arc flash burns. The ATPV is expressed in calories per square centimetre (cal/cm2).

Ebt Explained

The Energy Break-Open Threshold (Ebt) as defined by ASTM, is a measurement of a material's ability to withstand an arc flash before it ruptures or breaks-open, creating a gap that exposes the wearer to the arc. The Ebt is expressed in calories per square centimetre (cal/cm2) and indicates the incident energy level at which there is a 50% probability of the material breaking open, forming an opening of at least 1.6cm (0.5 inches.)

ATPV / Ebt Overview

  1. The ATPV and Ebt are evaluated in the same test.
  2. The first point to be reached, either the ATPV or Ebt, is the reported arc rating.
  3. If an Ebt value is determined and found to be equal to or below a determined ATPV, then the Ebt value is reported as the arc rating value and noted as Arc Rating (Ebt).
  4. If an Ebt value is found to be above a determined ATPV, then the ATPV value is reported as the arc rating value and noted as Arc Rating (ATPV).
  5. ATPV and Ebt arc ratings are expressed in calories per centimetre squared (cal/cm2). For example, a material with a determined ATPV of 12 would have an arc rating of 12 cal/cm2.
  6. A calorie is defined as a unit of energy equivalent to the heat energy needed to raise the temperature of 1 gram of water by 1 degree Celsius (now often defined as equal to 4.1868 joules). 

Neither measurement is better. Essentially Ebt fabrics are typically more insulative than they are strong and ATPV materials are stronger than they are insulative. 

Usually Ebt indicates the garment is a knit and is more comfortable but essentially no less protective to the user.  

Testing For ATPV And Ebt - DuPont™ Arc-Man® 

The open arc test determines the limit of the incident energy to which a material or material assembly will provide protection against the thermal effects of an electric arc. The electric arc testing system developed by DuPont™ measures the Arc Thermal Performance Value (ATPV) and Energy Break-open Threshold (Ebt) values of protective fabrics and garments in simulated open electric arc incidents according to IEC/EN 61482-1-1.