Definitions:
Arc Thermal Performance Value (ATPV): This value is presented in calories per square centimeter and represents the maximum capability for arc-flash protection of a particular garment. This rating also applies to fabrics. However, a garment made from more that one layer of arc-fl ash rated fabric will have a calories per square centimeter rating greater than the sum of the ATPV ratings of the original fabrics. The calories per square centimeter rating of most arc-fl ash protective suits, coveralls, and coats is commonly sewn into the fabric in large letters on the outside of the garment.
Flame Resistant (FR): “Flame resistant” can describe a fabric naturally resistant to burning but also can represent a material with special treatment applied to the fabric.
Occasionally, the letters FR are used to represent “flame retardant.” This can lead to some confusion because a flame-retardant treated fabric is flame resistant, but a flame-resistant fabric is not necessarily flame retardant. Flame Retardant: This term could be used to describe a fabric made up of a flammable fabric treated in such a way that it will provide arc-flash protection.
Fabric Weight: This is usually represented in one of two ways: ounces per square yard or grams per square meter. Both of these values essentially refer to the thickness of the fabric. The more ounces per square yard, the more material exists in the same square yard of fabric.
Heat Attenuation Factor (HAF): This is the amount of heat blocked by the fabric. Even though a fabric may be 100 percent flame resistant, that does not mean it will block all of the heat to which it is exposed. An HAF of 85 percent means that it will block 85 percent of the heat the fabric encounters. This applies to a short burst of arc-flash heat – typically less than one second. In the event of prolonged heat exposure, the HAF would be much lower.
Calories per Centimeter Squared: This is a number identifying the amount of energy that can be delivered to a point at a particular distance from an arc flash. Once this value is known, the ATPV rating of the flash clothing required for work at that distance from the potential flash hazard is also known.
Energy Break-Open Threshold (EBT): Primarily, this addresses the physical strength of the fabric with respect to thermal energy and at what arc-flash value the fabric will fail.
Personal Protective Equipment (PPE): This term is primarily used to describe all safety equipment used by personnel to protect personnel. This includes fall protection, confined space, electrical hazards, and so on.
Hazard Risk Category (HRC): This is a 2004 NFPA 70E rating of exposure levels for particular types of equipment. The values range from zero to four, with a zero HRC not requiring any ATPV-rated PPE. The minimum ATPV rating for Categories One through Four. (see Product Selector above)
*Thanks to www.electricityforum.com
