Selection of appropriate PC & electrical PPE should only be determined following an Arc Flash risk assessment and the calculation of the prospective arc incident energy. PPE is a key part of safety precations in substations.
Arc Energy Basics
Arc Rating
The Arc Rating is the maximum incident energy resistance demonstrated by a material prior to break open (a hole in the material) or necessary to pass through and cause with 50% probability a second or third degree burn.
Arc Rating is normally expressed in cal/cm² (or small calories of heat energy per square centimetre). National Fire Protection Association (NFPA) defines Arc Flash safety regulations for OSHA compliance. The categories of PPE as described in NFPA 70E are as follows:
| Hazard Risk Category | Required Minimum Arc Rating for PPE | Clothing Description | |
| Cal/cm2 | J/cm2 | ||
| 0 | n/a | n/a | Untreated Cotton |
| 1 | ≥4 | 16.74 | Arc Rated Flame retardant (FR) shirt, FR trousers or FR coverall |
| 2 | ≥8 | 33.47 | Arc Rated Flame retardant (FR) shirt, FR trousers or FR coverall |
| 3 | ≥25 | 104.6 | Arc Rated Flame retardant (FR) shirt, FR trousers or FR coverall, and arc flash suit selected so that the system arc rating complies with the required minimum |
| 4 | ≥40 | 167.36 | Arc Rated Flame retardant (FR) shirt, FR trousers or FR coverall, and arc flash suit selected so that the system arc rating complies with the required minimum |
Note that a hard hat with full-face shield and the appropriate gloves are required also.
An exposure of between 1 and 2 calories will cause second degree burn on human skin. An Arc Flash typically releases between 5 to 30 calories and energies of 30 to 60 calories are not uncommon.
Most Arc Flash injuries can be prevented if proper Flame Retardant (FR) PC & PPE is worn. The problem with non FR clothing is that during an Arc Flash, the high energy ignites the non-FR clothes, which causes body burn injuries and possible fatality to the wearer.
Process to select correct PC and PPE:
There are 3 steps required to determine the protection level of PC& PPE needed:
1. Carry out a Risk Assessment
This will involve an Arc Flash hazard analysis to determine the potential incident
heat energy caused by the Arc Flash. The analysis will focus on the probability of
the development of an arc fault and on the effects of a possible arc fault.
2. Determine the Arc Rating
This calculates the Arc Thermal Performance Value (ATPV) in cal/cm² and
determines the level of protection needed for the PC & PPE.
3. Select the PC & PPE
We supply the latest in Arc Flash Safety equipment, including Arc Flash helmets, Arc Flash Workwear, Arc Flash Switching Suits, Arc Flash Gloves and Arc Flash accessories.
We can advise you on the appropriate PC and PPE where you know your site specific categories and rating of Arc Flash hazards. If you do not have this information, we can recommend an independent company to you, who are experts in Arc Flash Studies, to carry out your Risk Assessment and calculate the Arc Rating required for you.
Read our guide on how to secure a substation and our guide on how to wash PPE as well.