Message #27695

[Neural]

Well, after going to the class, I was able to get an answer that satisfied my curiosity/paranoia. :)

when turning off an acetylene torch, you turn the acetylene off first because if you remove the oxygen, the acetylene has a potential to dirty the torch tip because it doesn't burn very clean just by itself.  This can lead to other complications in the future which are not so safe.

when turning off a propane torch, you turn the oxygen off first because the propane would sputter as it's volume tapered off, due to the oxygen forcing it out, thus causing the flame to jump from pocket to pocket (we're talking about a very small volume/space where this takes place), resulting in the popping sound.  Turning the oxygen off first allows the propane to continue burning, and because it burns cleanly, there isn't the danger of buildup inside the tip. :)