Originally posted by Wasp I can only guess that they turned the gas off further upstream before firing(!) up the welder.
No doubt! But I'm sure there's some tricky bits -- even when the gas is shut-off, there's residual pressure in the lines. At one point one of the workmen dressed up in a full kevlar suit, helmet, oxygen tank, mask etc. to work in the hole -- probably to remove the old tap and open up the main line to install the new tap.
The welder did not wear any protective gear beyond what an ordinary welder uses. After he was done, it was a little unnerving to see the gas main still smoking from the residual heat of welding on the new tap.
It was quite a production: at least six trucks, two trailers, a backhoe, horizontal directional drill, and a dozen men. Although it took then some time to get started in the morning, they were done and gone by early afternoon.