My mate got suspended from BG for allowing his apprentice to finish off soldering a joint on the meter union many years ago while the meter was disconnected but right under the pipe. Blew the lad about 20 yards and burnt all his face and chest. It was an industrial meter and still on lead it was that long ago, but when I did my apprenticeship with him he was paranoid so I always use a cap inside or remove and cover if working within a couple of metres.