ArcFlash - Glossary

Arc Rated (AR)

Used to describe Personal Protective Equipment and fabrics designed to offer protection against electrical arc flashes. Arc Rated fabrics are tested to ASTM D6413 to determine flame resistance, as well as a variety of other test methods. All of the required testing can be found in ASTM F1506 which is the performance standard for materials used to make Arc Rated clothing for electrical workers. One of the required tests is ASTM F1959, which is used to determine a fabric’s Arc Rating or the level of incident energy that it will protect against. Put simply: All AR garments are Flame Resistant but not all FR garments are Arc Rated.


ArcWear A Division of Kinectrics

Globally, ArcWear – A Kinectrics Company, is the most experienced company for arc flash testing, doing 90% of the world’s arc flash testing. Their reputation for accuracy and informative results is unsurpassed in the industry. Headquartered in Louisville, Kentucky, ArcWear receives more than 100 items for arc flash testing per month that are completed at their sister lab Kinectrics High Current Laboratory in Toronto, Canada.



Ablation is defined as the removal of material from the surface of an object by vaporisation, chipping, or other erosive processes. The term occurs in space physics associated with atmospheric reentry, in glaciology, medicine and passive fire protection.


A calorie is an energy measurement used to characterise the amount of arc flash energy which is required to cause a second-degree (blister burn) on human skin. Without protection, according to the Stoll Curve, it takes about 1.2 cal/cm 2 to cause a second-degree burn.


Energy Breakopen Threshold (EBT) is a rating assigned to Fire Resistent Clothing indicating the level of protection provided. EBT is used when ATPV cannot be measured due to flame-resistant fabric break open. EBT is also measured in calories per centimetre squared (cal/cm 2).


Flame Resistant (FR)

The property of a material whereby combustion is prevented, terminated, or inhibited following the application of a flaming or non-flaming source of ignition, with or without subsequent removal of the ignition source. FR clothing and garments made from those materials have the ability to self-extinguish (with an after-flame of 2 seconds or less) and will not melt or drip.

Hazard Risk Category (HRC)

Categories defined by NFPA 70E-2004 to explain protection levels needed when performing tasks. The values range from -1 to 4. ATPV rated PPE is required for categories 1 through 4 as follows:

  • Category 1: 4 cal/cm 2
  • Category 2: 8 cal/cm 2
  • Category 3: 25 cal/cm 2
  • Category 4: 40 cal/cm 2

HRC has now been replaced by PPE Category Levels


Heat Attenuation Factor (HAF)

This is the amount of heat blocked by the fabric. Even though a fabric may be 100 percent flame resistant, that does not mean it will block all of the heat to which it is exposed. A HAF of 85% means that it will block 85% of the heat the fabric encounters. This applies to a short burst of arc flash heat typically less than one second. In the event of prolonged heat exposure, the HAF would be much lower.

PPE Category Levels

The 2018 edition of NFPA 70E changed the way measurement is completed and PPE is selected. This most recent edition removed the concept of Hazard Risk Categories and the option to wear Non-FR/AR natural fibre garments in HRC 0 was eliminated. The standard now uses PPE categories which are based on an incident energy analysis.

Elliott Arc Flash Garments are now labelled PPE 1, PPE 2, PPE 3 or PPE 4.



The National Fire Protection Association.


NFPA 70E Standard

The standard that provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energised.


American Society for Testing and Materials.

Calories per centimetre squared (cal/cm 2)

This is a number identifying the amount of energy that can be delivered to a point at a particular distance from an arc flash. Once this value is known, the ATPV rating of the flash clothing required for work at that distance from the potential flash hazard is also known. See ATPV.

Arc Thermal Performance Value (ATPV)

Is a type of arc rating. It measures the incident energy that results in a 50% probability of a second-degree burn. When someone refers to an arc rating for their arc flash PPE, they are often referring to the ATPV that a garment has achieved. The ATPV is presented in calories per square centimetre and represents the maximum capability for arc flash protection of a particular garment. This rating also applies to fabrics, however, a garment made from more than one layer of arc flash rated fabric will have a calorie per square centimetre rating greater than the sum of the ATPV ratings of the original fabrics.


A calorie is the energy required to raise one gram of water one degree Celsius at one atmosphere. The onset of second-degree burns may occur at 1.2 calories per centimetre squared per second. One calorie per centimetre squared per second can be equal to holding your finger over the tip of the flame of a cigarette lighter for one second.




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