The Hazard Risk Category (HRC) is the level of ARC flash protection clothing you must wear to in order to be protected against a minimum level of incident energy that is measured in calories per centimeter squared.
In other words, electrical equipment, depending on its energy delivering capability, which can cause an explosion under fault conditions, or an ARC fault of a certain level measured in calories per centimeter squared.
That explosion can deliver a certain amount of heat to a certain distance.
Hazard Risk Category Levels
The NFPA® has identified four FR hazardous risk category levels, which are numbered by severity from 1 to 4.
Each level is considered a category, and is rated at a certain amount of flame resistance, which is also measured in cal/cm2.
HRC levels are based on specific job tasks, and are used to determine the necessary ARC rating of garments required to be worn during those tasks. You may be required to wear multiple layers of clothing in order to obtain the necessary rating required for your job.
The HRC levels range from HRC 1 (lowest risk), up to HRC 4 (highest risk).