On Dec 24, 7:08*am, Matty F wrote:
On Dec 24, 5:36 am, "mark" wrote:
*The reason for all of this is that some people still
have gas appliances with non-cut off pilot lights.

Non-cut off gas fires too.
Which are a lot bigger - 6kW input bigger for example :-)

"non-cut off pilot lights" - that sounds very dangerous.
Yet another reason why I won't have gas anywhere near the house.
There have been three emergencies with my neighbours' gas supplies.
I have an amusing video of workmen trying to seal a broken pipe.

Natural Gas is a) lighter than air b) very smelly due to additives.
You can get auto-cutoff valves if there is a full-bore escape
(vandalism of an outdoor pipe after the meter, BES do them - about £40
well spent if drugged up copper thieves in your area).

LPG is a different matter a) heavier than air b) smell doesn't reach
your nose, but can pool underfloors (basement, wooden ground floors)
until it finds an ignition source such as a low level socket or low
level socket timer and kaboom.

As to sealing a broken pipe, I suspect they use an "inflatable bulb"
which expands into the pipe sealing it off (the pressure is 75mbar
however the flow can be staggering if a large bore gas main). If it is
cast iron then just wrap in a self-amalgamating wrap of some sort.
When my mothers cast iron supply pipe was leaking the "apprentice"
thought he had found it and then slammed his spade right through it,
the Transco ACS at the time said "oh yeah, he's found it, clumsy sod".
The apprentice is now working in the nuclear recycling industry
now :-) Nice new yellow alkathene stuffed through.