Acetylene vs. Propane. Safety question.

[Neural]

I have heard the following:

Propane, then Oxygen when turning torch on. 
Oxygen, then propane when turning torch off.

BUT

Acetylene, then oxygen when turning torch on.
Acetylene, then oxygen when turning torch off.

Is there a difference in the gasses that is the reason for the variance in the on/off methods?

[Bluesssman]

I use acetylene and when it burns by it's self it releases a tremendous amount of black soot. Because of this I always turn the acetylene off first. When I start the torch, I like to have both on for the same reason. I know my torches so well (one set I have had for over 45 years) that I know how far to open each valve to get a good flame.

I have never used a propane/ oxygen torch, so I can't be much help there.


Gary

[Neural]

Hi Gary, thanks for the input. :)
Do you do your work in an area with a low ceiling (8' or 9'), and if so, do you have black spots on it from the use of the acetylene over the years?

[bobby1]

I also follow Gary's procedure....... turn the oxygen on slightly, open the acetylene slightly and light the flame. With a little practice you can get the feel of how much to open each valve so that there is enough oxygen to make the flame light without any dark soot.
Bob

[Bluesssman]

Hi Gary, thanks for the input. :)
Do you do your work in an area with a low ceiling (8' or 9'), and if so, do you have black spots on it from the use of the acetylene over the years?

I have had various height ceilings over the years, but no, I have not had any black spots because I never ran the acetylene alone. Also, now that I think about it, the acetylene soot settles rather than rise up to the ceiling.


Gary

[Neural]

I appreciate the info, though I have to admit it still doesn't really answer my original question in regards to propane.

The important factor that I'm looking for here, is why people say to turn the oxygen off *first* before turning off the propane, as opposed to the usual which is turn the Acetylene off first *then* the oxygen.

[Taogem]

Perhaps it is about the loud pop that happens that makes it best to turn the oxygen first ?

[Neural]

I have heard about the loud pop. 

Guess what it gets down to is I'm looking for a chemical/technical explanation of why, so I can understand what is happening and why. :)

[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. :)