When the National Fire Protection Association (NFPA) replaced the term "Flame Resistance (FR)" with "Arc-Rated (AR)" in its 2012 edition of the NFPA 70E, it stirred confusion among many.
What was the difference between FR and AR?
The short answer:
In order to understand the difference between the two terms, we will first look at Flame Resistant fabric and why it is important.
Flame Resistant (FR) clothing is very important because during a brief thermal hazard like a Flash fire or Arc flash, it's rarely that brief thermal hazard that kills people.
What does kill people? and cause the majority of the catastrophic injuries as well as the fatal ones, is that brief thermal hazard igniting flammable clothing. The flammable clothing continues to burn, lasting much longer than the initial hazard, and affects a much larger area of your body. And it is that surface area and severity that combine to cause most of the catastrophic and fatal illnesses.
How can we avoid this? Don't wear fuel.
This is where Flame Resistant, or FR, fabrics come in.
FR fabrics are fabrics that do not support combustion in air. This means that when the brief thermal exposure is over, the garment does not continue to burn. For this to happen, an important characteristic of the garment is that it is self-extinguishing.
The second characteristic needed in an FR fabric is that it insulates to the hazard so that you are not burned at all through the garment in addition to it not igniting and continuing to burn.
In short, there are two main reasons for wearing FR clothing:
Flame resistant clothing can also increase the chances of survival against electrical arc flash accidents.
The most commonly used test method to determine the flame resistant is ASTM D6414 Standard Test Method for Flame Resistance of Textiles.
All arc-rated clothing is flame-resistant, but not all FR fabrics have been arc tested. FR has many great characteristics, however we want to make sure that all the fabrics sold for arc flash protection have been tested against arc flash. So at the end of the day, you want a fabric that has an arc-rating.
AR indicates that a garment has an arc rating and the level of protection has been determined through testing.
Fabrics for personal protective garments are put through a Vertical Flame Test to measure and observe the response of materials to heat and flame under controlled conditions.
The fabric used to create arc-rated clothing is subject to additional tests, beyond the test methods for fabric labeled "FR." Primarily, it is exposed to a series of arc flashes to determine how much energy the fabric is able to block before it would cause the wearer to sustain a 2nd degree burn, 50% of the time. The result of this test, expressed in calories, is known as the Arc Thermal Performance Value (ATPV).
The change in terminology in the NFPA 70E was done to make sure acceptable clothing have an arc rating, and to exclude the use of fabrics that are considered FR under NFPA 701, which is a standard for draperies and upholstery.
The requirements for NFPA 701 are much different than those required by NFPA 70E, including the fact that 701 does not require the fabric to have been arc tested, nor an ATPV to have been established.
NFPA 70E states that fabrics must meet ASTM F1506, which requires that fabrics in protective garments be both flame resistant and arc-rated.
So all Arc Rated clothing is flame resistant; the official arc rating standard (ASTM 1959) requires fabrics be FR to even qualify for testing.
It's important to find FR fabrics or arc-rated fabrics that have been tested to specific industry standards, like NFPA 2112, Flash Fire Protection, or ASTM F1506 for Electric Arc Flash Protection.
Current standards for arc flash protection, detailed by NFPA 70E, state that all PPE clothing must also be flame resistant to qualify for an arc rating. In other words: all AR clothing is FR, but not all FR clothing is AR. The reason for this is that, based on the results of the tests mentioned above, equipment rated FR may not always provide the appropriate level of protection for workers who are at risk of facing arc flashes. These employees must wear the adequate level of AR clothing for the hazard so as to reduce the risk of serious injury or death by an arc flash.
In conclusion, Arc rating and flame resistant are two different things but are often confused because they go hand in hand. You can't have an arc rating without the material being flame resistant.