How It’s Tested: Episode 2 – The Vertical Flame Test, Straight Up

The Vertical Flame Test, ASTM D6413, determines whether a fabric is flame resistant or not, which makes it the test when it comes to arc rated and flame resistant (AR / FR) apparel. It’s important to note that there are other “flame resistance” tests in the market but ASTM D6413 is the only standard test method that is relevant to AR / FR apparel for secondary protective apparel in the United States. The others apply to other industries and are irrelevant for AR / FR clothing.

See the vertical flame test in action below and listen as Scott Margolin, Tyndale’s Vice President of Technical, as he provides an overview of the test and what the results tell us:

As shown in the video, the test is performed by taking a 12-inch long, 3-inch wide piece of fabric, securing it on three sides, and suspending it vertically in an enclosed vertical flame chamber. In the chamber, the bottom edge of the fabric is exposed to a controlled methane flame for 12 seconds. The flame is then removed from the fabric and one of two things happens:

  • The fabric self-extinguishes, that is, the fire goes out.
  • Or, it doesn’t. If the fabric continues to burn, it is not flame resistant and fails the test.

If the fabric self-extinguishes, it is removed from the chamber. There will be some char, on the bottom of the fabric from the flame. A weight is applied to the edge of the charred portion of the fabric and the fabric is allowed to rip. Measure how far that damage progresses and record the char length. Repeat the test five times, average the results, and depending on the standard, the average char length measurement determines whether the fabric passes the vertical flame test or not:

  • NFPA 2112 specifies that 4 inches or less passes.
  • ASTM F1506 specifies that 6 inches or less passes.

Two additional variables are measured as part of this test, however, these do not determine pass/fail of the test, they are simply recorded:

  • Afterflame, which is the number of seconds during which there is a visible flame remaining on the fabric.
  • Afterglow, which is the number of seconds during which there is visible glow remaining on the fabric.

ASTM D6413 is the most rigorous of the flame resistant tests in the market. It’s important to note that while D6413 is a component of flame resistant rainwear testing, it should never be taken as the appropriate standard in the absence of the other electric arc flash or flash fire rainwear tests.

How It’s Tested is our ongoing series exploring safety standards and test methods for AR / FR garments and PPE. Whether you are a seasoned professional or just starting out, follow along with this series to make sure you are up to date on the latest information. If you’ve missed it, our first episode can be found here. Stay tuned for much more content and helpful resources!

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