When turning off an oxyfuel torch, which valve must be turned off first?

When turning off an oxyfuel torch, the acetylene valve must be closed first to ensure safety. Acetylene is a fuel gas that is more flammable than oxygen, and it has a tendency to form an explosive mixture with air. By turning off the acetylene first, you minimize the risk of any unburned gas accumulating in the line, which could lead to an explosion if the oxygen valve is closed first.

Furthermore, by extinguishing the fuel gas supply before shutting off the oxygen, you also ensure that if any spark or flame is present, it is immediately quenched with the removal of the fuel. This sequence of shutting off the valves is a crucial safety procedure that helps prevent backfire and other dangerous situations that could arise from improper torch handling.