NFPA 701: Description of Test Methods
20.03.2012 § 2 Comments
(No. 2 of 3) The flammability test we use for all of our drapery fabrics is the ACT performance guideline: NFPA 701. The standard actually includes two tests, one for draperies that weigh less than 21 oz./sq. yd (Test Method #1, the replacement for the original small scale test) and a second for draperies that weigh more than 21 oz./sq. yd or have some kind of backing (Test Method #2, the replacement for the original large scale test).
It’s typically harder to predict how heavier fabrics or blackout linings will behave in real life, so Test #2 uses a life-size scale. The 4-foot long samples are folded and hung like draperies in a 7-foot tall testing chamber before they’re exposed to a flame. The test uses much more fabric, and it’s more expensive than Test #1.
It’s more common that we’ll test a new drapery fabric with Test #1. Ten samples (approx. 6” x 16”) are burned for each test, and whether the fabric passes depends on their average performance. One at a time, a sample is suspended vertically in the testing chamber with small weights at the bottom to keep it in place. A 4-inch flame is lit at the lower edge and held next to the sample for 45 seconds before it’s removed. Sometimes pieces of the fabric will break away from the rest of the sample; this is called drip burn. The tester will record how long the pieces burn after they’ve separated from the sample, and if the average drip burn for all ten samples is more than 2 seconds, the fabric won’t pass.
The second criterion for passing Test #1 is that, on average, the samples can’t lose more than 40% of their mass after they’ve burned. The specific percentage was decided because of a series of tests at the Southwest Research Institute (SwRI) in the 1980’s that showed that 40% tended to separate the “good” performers from the “bad” performers. Weight is a tricky measurement, though, because some fabrics hold moisture better than others; wool, for example, can be 15% moisture, which can affect both the weight measurements and how the fabric burns. To create a level playing field, all of the samples are “baked” at 220°F for half an hour beforehand.
You can read the complete NFPA 701: Standard Methods of Fire Tests for Flame Propagation of Textiles and Films on the NFPA website, and I will post some example test results in my next post.