To see if something is self extinguishing, do the same test that fire marshals do to test interior finish materials for the same thing...try to burn it. If it goes out once you remove the flame, it's fine.
Bjarney, I checked out that Arcwear site. And I must say that it's quite amazing, the difference in performance of the two rain jackets, under Arc Flash conditions. The jacket on the left, should be banned for use around linework and High Voltages!. Can't remember what it was made of, but I would sooner be wearing the one on the right.