NFPA 70E (2018) has identified various Flame Resistant Hazardous Risk Category levels. These are broken down into a total of four categories, ranging in severity from 1 to 4.
LEVEL 1 CONTAINS THE LEAST PPE, WHILE LEVEL 4 CONTAINS THE MOST.
For example, working with low-voltage wiring with minimal likelihood of an arc flash occurring would not require extensive PPE. On the other hand, working on a high-voltage machine involves a very serious risk of an arc flash, so a category 4 rated PPE is likely going to be needed in this case.
Each category includes the minimum Arc Rating value for the required PPE, which represents the amount of incident energy (in cal/cm^2, or calories of heat energy per square centimeter) on a fabric or material that carries a 50% probability of causing a second degree skin burn injury.
In other words, you have a 50% chance of being burned if exposed to an electric arc with the same number of calories of heat. The arc rating indicates the level of protection provided by Flame Resistant (FR) clothing measured in cal/cm^2. The higher the value the greater the protection.
A brief overview of each of these four PPE Categories is explained below:
The first category represents the lowest level of Arc Rated PPE, requiring only a single layer of arc-rated PPE.
Workers need the following clothing:
The second category can also be fulfilled with a single layer of Arc Rated PPE.
In PPE Category 2, workers need the following clothing:
PPE Category 3 and 4 require additional layers of PPE. Arc flash suit hoods are required and rubber insulating gloves and leather protectors, or arc-rated gloves are required.
For PPE Category 3, workers need the following clothing:
The final PPE Category requires AR clothing with a minimum rating of 40 cal/cm^2:
The categories of PPE as described in NFPA 70E are summarized as follows: