Happened in West Sussex in 1986.
Some workers using a hydraulic mole (which hammers its#
way through the ground), went through both a water main
and a medium pressure gas main.
Water spurted out of cooker hobs and gas boilers etc.
BG shut off the gas to a large part of West Sussex
South of Horsham.
The police commandered our village carpark so that BG
could use it as a base for all their vehicles and they
brought people in from all over the UK to visit
every house and shut off all gas appliances. Anyone at
work came home to find a note saying that the hole in
their drive or pavement was where BG had dug down and
cut and capped the gas supply to the house.
After fixing the damage and flushing out the water they
has to purge and repressurise the entire area and then
revisit every house to get gas appliances running again.
I did find a HSE report on the incident once, but have
forgotten where it was kept.
Well one way is that in many older systems the gas pipes are knackered. When
they dug up our road after reports of gas it transpired that our clay soil
was all that was containing a lot of the gas supplies, since the pipes had
rusted away, indeed as they disturbed the pipes gas started to bubble up in
peoples gardens and killed some plants, including one of my roses. They have
since used plastic pipes to replace them all, but as I have no gas
installed, they just left a stop end here ready in case its needed in
I was amazed that they let it go this far, but apparently its not uncommon
for water leaks to get into the clay and leach out in the gas supply, even
to cut it off on low spots.
Both gas and water have extensive contracts going on replacing the now very
old pipes, in the case of gas because they are obviously steel and rusting
away, and in the case of water mainly due to them being made of lead, which
although probably safe after all this time does deteriorate of course.
This newsgroup posting comes to you directly from...
Our old system had 70 year old steel pipes running along the back
gardens. Leading up to their replacement 3 years ago, they regularly
came along with a sniffer in case of serious leaks.
3 years ago, they laid a new plastic main at the front, along the road,
then up drives to the individual meters. There were too many garages
and extensions built over the original pipe route at the rear.
Understandable I suppose. I doubt they had in mind when the laid the
original pipes, that there would be much need to build so many
extensions and garages.
When the laid the new pipe, the homes to our right have a drive, but
there is no easy underground route to get a pipe from the front, to the
rear where their meters are. The result was gas feeds run on the
surface down the sides of those houses.
I gave the installers leave to run next doors supply pipe up my drive,
with my own buried supply pipe.
Lead pipes in soft-water areas never get a coating and remain soluble.
The water companies use phosphate dosing to prevent the water dissolving
small quantities of lead (I designed some of the dosing rigs in this
area). Other than that, lead pipes can last hundreds of years, as lead
is very stable.
Water flow undermined support for the gas pipe, it sagged and broke open
at a joint. I doubt if much (any) water would get into the gas pipe at
least until the gas pressure was turned off to prevent an explosion.
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