American Chopper episode got even more reckless

I still wonder about deflagration: how is it possible for acetylene to exit the acetone/pumice in the bottle, and travel up through the valve and to the regulator, at over 160psi, without deflagrating? Never heard a good explanation of this.

That's been covered several times in the thread by other posters. Part of it is the tiny amount of "free" acetylene involved, and part of it is that the open spaces between "the inside of the cylinder" and "the high pressure side of the regulator" aren't large enough to allow the acetylene molecules to "get a good running start", so that when they bang into each other, they don't have enough energy to trigger the initial breakdown and get the process started. I can *NEVER* remember the proper term for the mechanism involved, but at least two others in the thread have used it.