A CAT rating (short for PPE Category rating) identifies the level of protection that a FR/AR garment offers in the event of an arc flash.
The categories themselves correlate to a more specific measurement of protection known as the Arc rating. The Arc rating is measured in calories/cm² and determines how many calories of energy the garment can withstand from an arc flash. Arc rating is defined as the amount of energy a given fabric can withstand before a 50 percent likelihood of the onset of second-degree burn through the fabric. In other words, what is really measured is insulation.
| Level | calories/cm² |
|---|---|
| 1 | 4,0 cal/cm² |
| 2 | 8,0 cal/cm² |
| 3 | 25,0 cal/cm² |
| 4 | 40,0 cal/cm² |
Before revisions to the NFPA 70E standard in 2015 that altered the terminology, CAT ratings were known as HRC, or Hazard Risk Category. HRC levels were also on a scale of 1-4 and were correlated with identical minimum Arc ratings.