How It’s Tested: Episode 4 – ASTM F1506, Part 1: The Big Two Tests for Arc Protection

One of the main standards for arc flash-protective clothing is ASTM F1506, Standard Performance Specification for Flame Resistant and Electric Arc Rated Protective Clothing Worn by Workers Exposed to Flames and Electric Arcs. But don’t be distracted by its long formal name. Known more commonly as “the Arc Standard” or “the NFPA 70E Standard,” ASTM F1506 has a simple but important purpose: it’s used to identify arc-rated flame resistant (AR / FR) fabrics that can be worn for arc flash protection.

In fact, ASTM F1506 establishes minimum performance requirements for flame resistance, arc rating, and mechanical durability – using two main tests and a series of smaller tests to identify fabrics that comply – and includes labeling requirements.

Scott Margolin, Vice President of Technical, gives a run-down on the two “big” tests – those that determine flame resistance and arc rating:

Check back next week to learn more about the other tests for mechanical durability in episode 5.

What are “The Big Two,” and how do they work?

1) Flame Resistance

First, before it can even be considered for arc flash applications by being tested for arc rating, we must establish that a fabric is flame resistant. To determine this, ASTM F1506 uses ASTM D6413, “the Vertical Flame Test.”

As part of this test, a fabric sample is enclosed in a flame chamber and exposed to a flame vertically, from the bottom, for 12 seconds. The flame is then removed and either:

  • The fabric self-extinguishes (fire goes out). In this case, the fabric is then removed from the chamber, a weight is placed at the edge of the fabric, and the fabric is ripped along the charred portion. From there, the rip – known as “char length” – is measured.
    • To pass ASTM F1506 and qualify for arc flash protection, it must be 6” or less after 25 launderings.
    • On the flash fire side, NFPA 2112 requires a char length of 4” or less.
  • It keeps burning, in which case the fabric is not flame resistant and cannot qualify for arc flash protection.

2) Arc Rating

Once we have determined that a fabric is flame resistant, we need to quantify the thermal protection the fabric provides in an arc flash – specifically, how much heat it will block from an electric arc before the wearer experiences the onset of second degree burns. ASTM F1506 uses test method ASTM F1959, “The Arc Rating Test,” to measure this.

In this test, an arc is conducted in a lab on three fabric samples. This process is repeated 7 times, giving us 21 pieces of data (one from each fabric sample). These data points are plotted on a graph based on whether or not there was either a burn through the fabric or a hole in the fabric. To determine the fabric’s arc rating:

  • A computer analyzes the average of the data, running a curve through the points.
  • On the vertical axis, we find the 50% probability mark and draw a line from there to the black curve, then straight down from there to the bottom horizontal access.
  • This point on the horizontal access is the arc rating for that fabric – and any garment ever made from it. If applicable, the arc rating can then be used to identify the NFPA 70E PPE Category (CAT, formerly known as Hazard Risk Category or HRC) for a garment made from this fabric.

“Want to learn more about how arc ratings are determined? Check out Episode 7 which does a deeper dive on ASTM F1959.”

Garments that meet ASTM F1506 also comply with OSHA 1910.269, NESC, and NFPA 70E.

Look out for our next post to take a closer look at the remaining tests that ASTM F1506 employs to assess a fabric’s mechanical durability.

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