The letters “AR” stand for Arc Rated and the letters “FR” stand for flame resistant, ALL AR clothing is flame resistant (FR), but not all FR clothing has been Arc Rated.
The official Arc rating standard is ASTM 1959 (US) or EN 61482-1-1 (European) which requires fabrics to be FR and tested. To comply with the ASTM 1959 (US) or EN 61482-1-1 standards, 21 samples have to be subjected to arc flashes in a certified laboratory, where sensors measure the heat transfer through the fabric.
A calculation based on the Stoll curve modelling then predicts whether or not a second-degree burn would have resulted. The model calculates the energy likely to cause a second-degree burn through that fabric 50% of the time. This number is expressed in calories and then becomes the arc rating for that fabric and any garment made from it.
The arc rating measures insulation of FR fabrics to an arc flash. The arc rating can be reported as ATPV (Arc Thermal Performance Value) or Ebt (Energy Break open threshold) – the higher the value, the more protection the material offers.
All AR garments must have an internal label and external label which clearly indicates the HRC (Hazard Risk Category) and the ATPV or the EBT value that the garment has been tested and approved for. The HRC enables the user to identify the risk category of the work that needs to be completed and the required Arc Rating of their clothing to ensure that they are adequately protected. It is critical that the worker is covered from “head to foot” with the correct rated and tested PPE and PPC to ensure their safety.