On Dec 3, 10:48 am, Edge wrote:
After I had my house built, I noticed that the natural gas line to the
dryer did not have a shutoff valve. The builder sent over a plumber to
install one. Without turning off the gas, he unscrewed the end cap,
doped up the threads, and screwed in a shutoff valve. Although it only
took less than a minute, was this safe? This was located in the
basement near the furnace and water heater, which could have provided
an ignition point. I never had to shut off the gas to the whole house.
For my information, where is the main shutoff for the gas?

Was this safe? No. Is it common? I wouldn't be surprised.

When I had my furnace installed, we discovered that the main shut off
inside the house turned off the gas to all the appliances except the
furnace. The pipe to the furnace was T'd before the main internal
shutoff. In order to shut off the gas to the furnace, we would have
had to shut off the valve at the meter outside the house, which would
have required a service call to the gas company to turn it back on. We
opened all the doors in the basement and the installer removed one
section of pipe at a time, installing a nipple with a cap as he got
the next section ready. Eventually he rerouted the pipe to where it
had to go, with each section only being open for a matter of seconds.
With the air movement from the doors open we barely smelled any gas
during the process.

I will note that the installer determined which pair of pliers he
would use to turn off the gas at the meter and kept them handy
throughout the rerouting in case he had to turn the gas off.