Gas is crazy. The only time I needed to have gas pipes rerouted, it needed a change before the meter and the shut-off valve. So the gas company guys started the work ... by cutting a live gas pipe, intentionally lighting the leaking gas on fire, and welding a connection while the not-yet-welded hole was acting as a small flamethrower. Apparently that's considered safe to do with low-pressure small diameter pipes, but it seemed absolutely, totally insane.

burning gas never builds up to explosive concentrations, so it is what they do. I've heard other stories. A friend of mine cut a gas main digging, and when he called emergency they told him he should have lit a match instantly, it is too late now just evacuate the neighborhood. (the gas company was mad until he pointed out the gas main markings a safe distance away from where he was digging)