Question

As some of you may know, at times, a gas line underground may leak or be hit by a excavation company or other reasons. When this happens, usually it is a type of plastic pipe that they use almost exclusively now for new gas lines which is called polyethylene, or, PE for short. There are many kinds of gas piping materials out in the country but this is the most common new installation and usually, the easiest to repair if something were to be hit. Some line are made of PVC (very dangerous),black iron steel, cast iron steel, etc. The reason I spoke about the excavation hitting lines at times is because when a PE line is hit, it can be squeezed at both ends and the repair can take place right there. But what about a steel line that is hit? It isn't possible to squeeze a steel line, they can isolate the gas at different valves but the result will be the loss of homes in the thousands typically and the relight process is daunting. So how would they be able to repair a steel line if they wouldn't isolate the lines at valves? They would actually weld right there the hit is, with gas blowing out of the pipe. But how? Wouldn't they cause an explosion? Any thoughts?