What is an arc flash rating?

When working in areas where an arc flash is possible, it is important to know what the risk is, and how to best protect those in the area. To help with this, NFPA 70E-2000 established Hazard Risk Categories (HRC) based on different duties in the workplace. These ratings are given to different types of clothing and equipment that can provide protection against an arc flash or other electrical event, but since 2015 has been replaced with "PPE Categories." 

The ratings start at HRC 0, which offers virtually no protection, up to CAT 4, which is the highest level of protection listed. The different levels are broken down based on the minimum arc rating of the PPE in calories per centimeter squared.

Hazard Risk Categories

Arc flash PPE CategoriesThe following are the four hazard risk categories, examples of each, and what type of arc flash rating it provides. 

  • HRC 0 – This is pretty much any type of normal clothing including long sleeve shirts, pants, hearing protection, safety glasses, and more. It provides protection from 0 cal/cm², so it is insufficient for staying safe from any type of arc flash.
  • CAT 1 – This is arc rated fire-resistant shirts and pants, or a arc rated fire resistant coverall. It consists of just one layer of true personal protection equipment, and is rated to provide arc rating of 4 cal/cm².
  • CAT 2 – This level of rating is also going to consist of the same types of PPE as CAT 1, but it will either be better made for additional protection, or an additional layers will be worn. This will provide protection 8 cal/cm².
  • CAT 3 – This level includes the same items as CAT 2, but along with an arc flash suit that meets the established arc rating requirements. This will be at least two, and sometimes three, layers of protection. At this level the minimum arc rating is 25 cal/cm² of protection.
  • CAT 4 – Here it is the same items as CAT 3, but with higher quality and protection levels. There should be three to four separate layers that are being worn, which will provide protection of at least 40 cal/cm².

Remember, arc rated PPE is no longer assigned a hazard risk category but as a PPE category!

 

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