Flame Resistant (FR) and Arc rated (AR) Clothing, these 2 terminologies are very often being heard about in the PPE industry today. As per NFPA70E, what was earlier referred to as Flame resistant (FR) clothing is now called Arc Rated (AR) clothing.
A simple note defines the difference between these 2 terms – ALL clothing with an Arc rating (AR) is Flame Resistant (FR), but not all FR clothing has an Arc rating. AR clothing are designed to protect the wearer against Arc Flash. The level of the AR clothing is defined by how much heat energy the fabric is able to block.
Flame resistant clothing is known to provide two-fold protection:
- Against Flame:
FR clothing is worn to guard against flame during an accidental fire situation. Protective clothing is put through Flame Test, as per various standards like ISO 15025, ASTM D6413 etc. to determine the protection level of material under controlled conditions.
- Insulates the wearer against heat hazards:
Insulation against heat hazards is the second function of FR clothing. Flame resistant clothing provides the wearer protection from various heat related hazards like radiant heat, convective heat, contact heat etc. and can lessen the impact on the area directly affected by the accident.
To be an Arc rated (AR) fabric, it must first be a FR fabric. Depending upon the weave construction, blend and weight of the fabric, it may offer different levels of arc protection.
According to the various arc rating standards like ASTM F1959, IEC / EN 61482-1-1 clothing needs to be FR before it can even be tested to determine its Arc rating.
How an Arc Rated fabric (AR) is tested?
For the ASTM F1959, IEC / EN 61482-1-1 testing, 21 samples of textile material are subjected to an arc flash and heat transfer is measured through the fabric using sensors. Stoll curve model predicts whether or not a 2nd degree burn would result by use of the textile material and also calculates the energy likely to cause the onset of 2nd degree burns through the fabric, 50% of the times the material is tested. This energy level determines the Arc rating of the textile material. This energy is expressed in calories per centimeter square (cal/cm²). The arc rating can be reported as ATPV (Arc Thermal Performance Value) or EBT (Energy Breakopen Threshold). ATPV and EBT may both be evaluated in the same test, but the first point to be reached is reported as the arc rating.