"Ed Sirett" wrote in message
news
On Wed, 14 Jun 2006 13:23:40 +0100, PM wrote:

A couple of questions regarding extending gas pipework:

1) It is illegal to run gas pipe in a cavity wall because of the
possibility
of gas build-up, does this mean it is preferable where I have the choice
to
run gas pipe along a wall rather than under floorboards?

2) How do I clear the existing pipe of gas before soldering the new pipe
on?
The pipe comes down from the meter, under the floor (presumably
horizontally
but I've got no way of telling) and then up in a cupboard which is where
I
will be making the join. So I would imagine most gas will escape once I
open
up the old pipe - but with things like this it is best to make sure!
Should
I open up the test nipple at the meter to aid dispersion? I don't have
any
gas analysis devices.
N.B. I am fully aware of the need to purge air from the new
installation.

As always if you need to ask you probably shouldn't be doing it...

1) Through cavity is fine but there are extra rules. See BS 6891

2) No need to purge gas from the pipes. You will need to seal the meter
outlet if working within 2m of the meter. The gas can only burn if comes
into contact with air. Even when unsoldering fittings the most you even
get is a small flame which goes out in a few seconds.


When I cut the old pipe ready to solder the new pipe on, won't the gas mix
with air at that point? The old pipe is vertical up a wall and I will be
cutting it about a foot from the floor. Won't the gas will rise out of the
existing pipe so could be in the 5-15% concentration either above the pipe,
or within the pipe?