It's hypothetical...
I was doing some water plumbing today and where I had a 15mm copper pipe going though the wall, I decided it was probably a good idea to sleeve it with a bit of plastic conduit[1] - just to stop the pipe rubbing on the brick due to expansion.
Despite pushing the sleeve almost out the other side for the duration, soldering the elbow on the pipe right up against the wall burnt the sleeve. Guess the gas flame must have licked in the hole. Oddly enough the emulsion barely discoloured and did not burn.
Not a problem this time - I can shove a new sleeve on from the other side.
But, how do gas folk avoid this problem when soldering up against a sleeved hole? We'll assume that the other end is connected to something so you can't just pull the pipe out to make the joint.
Any tricks on heat shielding could be helpful for what I'm up to.
[1] I thought about using 22mm copper as the sleeve - but then I'd have to hacksaw and de-burr it, so I tried the lazy option - and it got me thinking.