What is Arc Flash Rating?

When working with energized equipment, it is crucial to understand the level of protection your arc-rated garments are providing to you as the wearer. In order to measure the level of protection arc flash clothing provides, arc flash hazards were introduced in the 1995 edition of NFPA 70E. NFPA 70E had been working on deriving new safety standards for those working with electrical equipment for some time at the encouragement of OSHA (Occupational Safety and Health Act). Since the introduction of arc flash hazards, new warning labels and requirements have come out in the 2000s. 

What is an Arc Rating?

Arc ratings are the measure of protection that a fabric or material affords the wearer during an electrical arc event. These ratings indicate a material’s ability to insulate from a second-degree burn. Arc ratings are represented as the number of calories that can be absorbed if exposed to an electric arc. Garments with a higher arc flash calorie rating are considered to be more protective. 

How is Arc Rating Derived?

Oftentimes, arc ratings are derived via rigorous arc flash testing, which assesses how a material responds to an electrical arc. Understanding how to calculate arc flash rating involves testing materials in controlled conditions and measuring energy transfer to establish protective thresholds.

What is Arc Flash Testing?

Arc flash testing involves the process of testing materials and equipment to discover their arc rating. To test a material’s arc rating, an open arc is exposed to the item being tested in a lab. During testing, energy is measured as it passes through the materials and is compared to the Stoll curve. This gives an understanding of the level of survivable burns.  

An arc flash test involves a copper fuse wire that is placed between two electrodes that is then used to solicit an arc flash that delivers energy to the items being tested. The standard for the current is 8,000 amperes. The sample is then exposed to 2-150 cycles from a 50-60 Hz supply. It should be noted that exact current levels and number of cycles can vary based on testing protocols and standards.

Arc Flash Rating Chart

There are five arc flash category rankings ranging from HRC 0 to CAT 4. 

HRC 0 - In this category, no protective gear is worn, providing a protection level of 0 cal/cm².

CAT 1 - This class consists of a single layer of protection, such as arc-rated shirts and pants, achieving an arc flash calorie rating of 4 cal/cm².

CAT 2 - This level includes the PPE mentioned in category 1 with additional layering, providing protection of 8 cal/cm².

CAT 3 - At this level, an arc flash suit is introduced alongside the elements worn in CAT 2, offering an arc flash suit rating of 25 cal/cm².

CAT 4 - This is the highest level, providing the most protection against arc flash, featuring extensive PPE capable of protecting at least 40 cal/cm².

Before deciding on what level of PPE to wear, a risk assessment of the job and job site should be conducted to help determine the specific hazards present in the work environment. This can help aid in choosing the appropriate level of protection.

Arc-rated gear does not make up all of the gear that should be worn while working on an energized job site. Additional PPE is oftentimes needed which may include hard hats, gloves, and face shields which are crucial for full protection.

Type of Arc Ratings - EBT vs. ATPV

The ASTM (American Society for Testing and Materials) recognizes two arc ratings that measure the incident energy on a material. These two arc ratings are ATPV and EBT. 

ATPV (Arc Thermal Performance Value) - Is a measurement of the heat transfer through the fabric that causes the onset of second-degree burns. This is based upon the Stoll curve. ATPV will likely not breakopen and is thus considered stronger yet less insulative.

EBT (Energy Breakopen Threshold) - Is a measurement of the amount of energy needed to breakopen a material. This breakopen area is identified as an area of at least 1.6 cm² (0.5 in.²). This breakopen occurs before the onset of a second-degree burn. EBT is considered to be more insulative and less strong than ATPV since it will breakopen before it burns. 

To be labeled as ATPV or EBT, garments must pass rigorous testing and meet the ASTM F1506 standard. These garments must be properly labeled to ensure compliance with standards. Neither EBT nor ATPV is considered superior. Your choice depends on your specific safety needs.

It’s also important to note that the terminology and standards may continue to evolve, so referencing the latest standards from organizations like NFPA and ASTM is recommended for the most current information.

Order Arc-Rated Clothing from Majestic Fire Apparel

Majestic Fire Apparel offers a wide selection of arc-rated clothing ranging from beekeeper-style jackets to undergarments. We are based in Lehighton, Pennsylvania, and take pride in our work.  Looking for arc flash gear? Please reach out to our team or find a dealer today.