Which valve should be turned off first when extinguishing an oxyacetylene torch?

When extinguishing an oxyacetylene torch, the acetylene gas valve should be turned off first. This procedure is crucial for safety reasons. Acetylene has a more significant risk of backfire due to its instability and the way it interacts with oxygen.

By shutting off the acetylene gas first, the flame can be extinguished while ensuring that no residual acetylene remains in the system, which could create a hazardous situation. Once the acetylene is off and the flame has been extinguished, the oxygen valve can then be closed safely. This two-step process helps to minimize the risk of backfire and ensures a proper shutdown of the torch.

Following this procedure reinforces safe practices when working with flammable gases and equipment, which is a core aspect of handling oxyacetylene torches in a controlled environment.