The HRC (Hazard Risk Category) is established by the minimum amount of calories per square centimetre (ATPV or Cal/cm2). Any garment or garment set tested must result with a 50% probability of a 2nd or 3rd degree burn occurring to the wearer. The higher the result, expressed in ATPC or Cal/cm2, the higher the HRC level achieved.
There are five risk levels of 0, 1, 2, 3 and 4. Level 0 is where there is little or no risk, and level 4 is an highest or most dangerous level of risk. The chart below shows the 5 levels, with typical garments for each level, typical layering requirements and the minimum Arc Rating requirements for each category.