Behind the Arc Rating: Flammability

ASTM D6413-15 Standard Test Method for Flame Resistance of Textiles (Vertical Test).

This is one the most important tests we run here at our lab in Louisville, as it is among the required testing in ASTM F1506-15 Standard Performance Specification for Flame Resistant and Arc Rated Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards (try saying that three times fast!).

ASTM D6413, the Vertical Flame Test, is always the first we complete of the F1506-15 performance spec.  Why the emphasis on always? Well…

Primarily, the Vertical Flame Test is relatively quick and inexpensive, so if we can catch a failure on a fabric quickly, we can save our clients the time and money in arc flash testing! This does not mean that because the fabric passed the vertical flame portion of F1506  that it will definitely pass the arc portion, but it is a good predictor of flame resistance especially of flame retardant treated cottons.

So what exactly is the ASTM D6413-15?

“This test method is used to measure the vertical flame resistance of textiles…”–paraphrased from ASTM D6413-15 Standard Test Method for Flame Resistance of Textiles (Vertical Test)

We place the conditioned samples in a specific set of clamps individually and expose them to a 1.5 in (38 mm) flame for twelve seconds. When the flame is extinguished, we record the Afterflame (the amount of time a sample maintains a flame after the ignition source has been removed) if any; As well as the Afterglow (the amount of time the embers on a specimen glow after the ignition source has been removed).  Finally, using a specially designed hook and a specific weight to tear a specimen along the charred portion of the fabric. The torn length is measured as the Char-length.

According to the ASTM F1506-15 specifications, samples shall average less than a two second afterflame, a char length no greater than 6 in (152 mm), and no occurrence of melting and dripping. This is done both on pristine fabric, and on samples that have been laundered 25 times per AATCC 135-12 (Method: 3, IV, A iii). This determines if the fabric retains its flammability resistance after standard use.

ASTM D6413-15 is a common test method, and the standard itself doesn’t have any degree of pass or fail, but rather it gives us raw data that we can use to compare with standard performance specifications. If the data from the D6413 test meets the requirements for the F1506 specifications, we can continue the rest of the F1506 testing methods.

ASTM D6413 is not a stand alone criteria for flame resistance.  In the 1970’s that was the case, but over time fabric manufacturers developed ways to treat polyester and nylon to pass this test making it useful only in production testing of fabrics of known performance in the full scale tests like ASTM F1930 for flash fire and ASTM F1959 for arc flash.

We’ll have more on other tests in coming weeks!

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