Shutting off an Oxyacetylene Torch

Although learning the correct procedure for pressurizing, starting, and striking an oxyacetylene torch is obviously of the utmost importance in being able to use the implement at all, ascertaining how to turn the torch off while it is running is of equal consequence. Here, again, the correct procedure for shutting down the torch is a matter of debate and disagreement among different welders. There is also argument over whether the remaining gas in the hoses and regulator should be bled off or left for use during the next day’s work.

Some hold that acetylene valve on the torch itself should be shut off first, and the oxygen valve second, while others contend that the oxygen valve should be to first to be shut off. Those who advocate the oxygen-first method note that shutting off the acetylene valve first produces a loud pop of combustion, which could signal the potential for a flashback fire in the hose, and in any case fills the torch tip with soot. Those who are in favor of the acetylene-first method hold that the opposite technique is actually more dangerous. There is insufficient evidence to definitively choose between the two, although the oxygen-first method does leave the torch tip cleaner and less clogged with soot.

Once the torch is decisively turned off, regardless of the exact shut-off sequence you choose to adopt, the regulators on both cylinders should be completely closed to cut off all gas movement between the bottles and the hoses. The exact sequence does not matter in this case.

After this, however, another decision must be made by the welder, which will once again be a personal judgment call. You will need to choose, largely by following your own common sense and what your gut feeling of correctness is, whether to leave the gas that is trapped in the hose where it is, to be used in tomorrow’s welding, or whether to drain it or “bleed” it off and leave the hose empty.

The factors in favor of leaving the gas in the hose for the next day are numerous and fairly persuasive. Those who support this view point out that there is usually only a fire hazard in the event that your regulators or hoses are damaged or contaminated with oil and gasoline – in which case you should not be using them in any case. Leaving the gas in the hose means that you will not be wasting the gas, which is not cheap – nor will you be placing more of it into the environment than strictly necessary. It will also be a ready-made test to see if your system is leaking.

Safety and fire prevention are the main arguments for bleeding the gas out of the hoses, and these are also considerations that carry considerable weight. Although using undamaged, uncontaminated hoses and regulators will reduce the already small risk of a fire to a miniscule risk, there is still a risk, however slight, that a blaze or explosion will occur. If the gas is bled off, there is no danger at all. Therefore, it is up to the individual welder to decide the balance between slight risk and the complete assurance of safety.