Arc Flash 101: 5 Things You Should Know

NFPA 70E, OSHA, HRC, PPE - When it comes to arc flash standards in the industry, there are so many terms to remember and so many opportunities to misunderstand their meanings & requirements. These arc flash terms and standards may seem confusing, but it's important to understand each one so that you can comply with these standards and most importantly - stay safe. 

We're breaking down arc flash standards: hitting all the details - from standards to fabrics, and beyond. Here are five things you need to know about arc flash.

1.) What exactly is an arc flash?

It's a pretty straight-forward question, but it's important to know exactly what an arc flash is. 

An arc flash is: 
     • Caused by an arcing fault - a type of electrical explosion due to a rapid release of energy 


This is what happens when an arc flash occurs

 • Pressures generated 100's - 1,000's lb/ft
 • Sounds due to pressure waves can exceed 160 dB 
 • Debris & molten metal can reach speeds that exceed 700 mph 
 • The flash can reach temperatures in excess of 30,000 degrees Fahrenheit 
 • Extreme temperatures can vaporize copper wires with an estimated expansion of 67,000:1 

It's clear that arc flashes can be a very real danger in the workplace, which is why there are standards to keep workers safe. 


2.) What are the applicable standards?

NFPA 70E-2015 and OSHA 29 CFR 1910.269 are two standards that protect against the dangers of arc flash – but they aren’t identical. Before we get into how they differ, let’s summarize the purpose of each.

NFPA 70E-2015 is a standard of the National Fire Protection Association, and is the consensus ‘Standard for Electrical Safety in the Workplace’. It began in 1976 to assist OSHA, and was published in 1979.


The purpose of NFPA 70E-2015 is to provide a practical, safe workplace relative to the hazards associated with electrical energy:
     • Acts as a guide to avoiding injuries
     • Assists users in complying with OSHA. 

NFPA 70E-2015 is related to NFPA 70 – the National Electric Code®. The purpose of NFPA 70 is to minimize the risk of electricity as a source of electric shock and as a potential ignition source of fires & explosions.
On the other hand, there’s OSHA 29 CFR 1910.269, which is an arc flash law for power generation, transmission, and distribution. 

NFPA 70E-2015 is a standard, while OSHA 29 CFR 1910.269 is a law with a variety of different regulations.
The truth is, there are actually similarities between NFPA 70E & OSHA 29 CFR 1910.269.

Arc flash PPE (Personal Protection Equipment) requirements for both NFPA 70E & OSHA 29 CFR 1910.269:
     • Conduct a hazard analysis to determine your arc rating requirements
     • The arc rating of your PPE should exceed your calculated risk
     • FR/AR (flame resistant/arc-rated) base layers are not specifically required, but greatly

The quick clip below visualizes the difference between flame resistant fabric and non-flame resistant fabric. (Non-flame resistant shirt shown on the left vs. flame resistant shirt shown on right)


3.) What is the difference between FR (flame resistant) & AR (arc-rated) fabric?

The most important thing to remember here is that ALL arc-rated fabrics are flame resistant. NOT all flame resistant fabrics are arc-rated. 

Flame resistant fabric undergoes a Vertical Flame Test (ASTM D6413). To be considered flame resistant, the fabric must:
     • Self-extinguish within 2 seconds or less
     • Not melt or drip
     • Have a char length of 6” or less

Arc rated material must be rated as Flame Resistant per ASTM F1506. This includes a Vertical Flame Test to prove flame resistance, in addition to being tested per ASTM F1959 to determine the fabric’s arc rating.

Different types of PPE must meet the requirements of different ASTM specifications in order to be labeled as AR (Arc Rated)

     • Clothing – ASTM F1506
     • Rainwear – ASTM F1891
     • Face protective products & hoods – ASTM F2178
     • Arc Protective Blankets – ASTM F2676 


4.) How is PPE rated for Arc Flash?

There are two values that represent an arc rating and many wonder if one rating is better than the other.

ATPV is the Arc Thermal Performance Value and represents incident energy that results in 50% probability of a second degree burn.

Materials with an ATPV rating tend to be stronger but offer less thermal protection. Example: 8 cal/cm2

The other rating is the Ebt – Energy Break Open Threshold. This rating represents incident energy that results in 50% probability of a break open. The material breaks open during arc testing before a burn could be registered.

Both ATPV & Ebt ratings may be reported, but the lower of the two ratings defines the official arc rating of the garment and must be on the garment label. 


5.) What do you need to wear to be safe & compliant? 

NFPA & OSHA share this general requirement for coverage:
     • Clothing shall cover potentially exposed areas as completely as
     • Shirts, coveralls & jackets shall be closed at the neck
     • Sleeves shall be fastened at the wrists
     • Shirts shall be tucked into pants

Different levels of protection are defined into 4 different PPE categories (formally referred to as HRC or Hazard Risk Categories).

Remember, a hazard risk assessment needs to be performed in order to fully understand your specific hazard and the protection it requires.

Below are a few examples of some of the arc flash ensembles we have to offer for each PPE category. From category 1 base layers to category 4 arc flash suits, we’ve got you covered - literally. 



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