I ran a gas line last year and caught a whiff when I was done. I had struggled slightly when lining up the union and thought I would check there first. But I said this out loud and before I could move the senior tech had his lighter out and lit the small leak at the union. Nice little blue flame.
The senior tech I was under years ago did that in a church attic. Wasn't a lot of room to move, needless to say I almost made a new access hole when he pulled out his lighter. First time I had ever seen that, didnt know what to expect.