Gas main fears

MouldyOldDough

We are getting the sewers on our extension connected next week 

This involves the gas main / feed to the property being somehow avoided (it cuts at 90 degrees across the path of the sewers)

Its not that I don't trust the builders not to hit the gas main but....

If they did cut the flexible yellow pipe with the digger - what would happen ?

Gas would pour out - but how would it be stopped ?

There's NO stopcock to turn - is there some remote shut off or would the road have to be dug up to find the connection (not an instant fix - and in the meantime, lots of explosive gas would be pouring out of the pipe.......

grumbler

Gas pressure in distribution pipes is very low. I think you'll need call Cadent emergency, but meanwhile any tight plug/seal will do the job.

MattMattMattUK

MouldyOldDough said:

We are getting the sewers on our extension connected next week 

This involves the gas main / feed to the property being somehow avoided (it cuts at 90 degrees across the path of the sewers)

Its not that I don't trust the builders not to hit the gas main but....

Firstly, have they done the prep work correctly? Have the contacted the network, have they had approval? If not then you should not trust them. Also, do you mean the gas main, or a residential supply pipe?
https://cadentgas.com/help-advice/digging-safely

MouldyOldDough said:

If they did cut the flexible yellow pipe with the digger - what would happen ?

Gas would pour out - but how would it be stopped ?

It will not pour out as it is a gas, it but it will leak, at considerable pressure. Depending on where you are on the supply route and how much of a leak they create the supply may automatically cut off at a local control point as loss of pressure results in the system shutting that section of the main, or it may need the network to intervene tackling it at shutoff valves. 

MouldyOldDough said:

There's NO stopcock to turn - is there some remote shut off or would the road have to be dug up to find the connection (not an instant fix - and in the meantime,

There are automatic and manual shutoffs at various intervals on the network. Then, once fixed the local network needs to be re-pressurised, with every premises connected to the depressurised section visited and manually tested and restarted. Whoever damages the pipe will be liable for considerable costs. 

MouldyOldDough said:

(not an instant fix - and in the meantime, lots of explosive gas would be pouring out of the pipe.......

Mains gas is not really explosive. It is flammable and when it is allowed to build up in an enclosed space and then ignited it can cause an explosion from the increase in pressure, but if leaking outside for example it requires fairly considerable effort to ignite and it is likely to burn, it would lack the enclosed space to allow it to explode. It would also only burn the amount that escaped into the air where it could mix and burn the oxygen in the air, it cannot burn in the pipe as it lacks an oxidiser. 

Ayr_Rage

My gas pipe fractured during the installation of my smart meter, a large lump of putty stopped the leak as it is only low pressure gas.

The installers called out the emergency team who fixed the issue as it was on the supply side of my meter.

They told me there is no way to cut the supply in the street and they even "welded" a new plastic pipe whilst the supply was live with their special machine.

If they do disturb a pipe I am sure they'll know what they have done and it will be fixed quickly.

FreeBear

Ayr_Rage said:

My gas pipe fractured during the installation of my smart meter, a large lump of putty stopped the leak as it is only low pressure gas.

Had a bunch of muppets installing a storm drain the length of my road. Prior to the team starting work, someone had been out and marked where utilities were in relation to the (to be dug) trench. 'Erbert missed my gas supply as it is a plastic pipe - Instead, had marked the kerb where an old unused pipe was.

Crew started digging up the road, cut through water pipes to a couple of the properties, and eventually got up to my house. Told them exactly where my live gas pipe was, and they said they'd be careful. They still cut through the pipe ff...s... Temporary fix was to just fold the pipe back on its self, and make an emergency call to Cadnet. Yes, they got an earful from me and Cadnet, along with yet another hefty bill.

MouldyOldDough

MattMattMattUK said:

MouldyOldDough said:

We are getting the sewers on our extension connected next week 

This involves the gas main / feed to the property being somehow avoided (it cuts at 90 degrees across the path of the sewers)

Its not that I don't trust the builders not to hit the gas main but....

Firstly, have they done the prep work correctly? Have the contacted the network, have they had approval? If not then you should not trust them. Also, do you mean the gas main, or a residential supply pipe?
https://cadentgas.com/help-advice/digging-safely

MouldyOldDough said:

If they did cut the flexible yellow pipe with the digger - what would happen ?

Gas would pour out - but how would it be stopped ?

It will not pour out as it is a gas, it but it will leak, at considerable pressure. Depending on where you are on the supply route and how much of a leak they create the supply may automatically cut off at a local control point as loss of pressure results in the system shutting that section of the main, or it may need the network to intervene tackling it at shutoff valves. 

MouldyOldDough said:

There's NO stopcock to turn - is there some remote shut off or would the road have to be dug up to find the connection (not an instant fix - and in the meantime,

There are automatic and manual shutoffs at various intervals on the network. Then, once fixed the local network needs to be re-pressurised, with every premises connected to the depressurised section visited and manually tested and restarted. Whoever damages the pipe will be liable for considerable costs. 

MouldyOldDough said:

(not an instant fix - and in the meantime, lots of explosive gas would be pouring out of the pipe.......

Mains gas is not really explosive. It is flammable and when it is allowed to build up in an enclosed space and then ignited it can cause an explosion from the increase in pressure, but if leaking outside for example it requires fairly considerable effort to ignite and it is likely to burn, it would lack the enclosed space to allow it to explode. It would also only burn the amount that escaped into the air where it could mix and burn the oxygen in the air, it cannot burn in the pipe as it lacks an oxidiser. 

No idea whether they have informed the network - I assume that they know what they are doing, they are not a fly by night company !

At least two of them tend to smoke constantly though - so listen out for a loud bang -  if they do hit the gas pipe/ hose - with the mini digger !

jefaz07

They don’t need to inform the network and don’t need approval. It’s your garden. 

The gas won’t shut off if it leaks either, nor will the network slam shuts operate. And they certainly won’t close any valves to stop it!! I have no idea where any of that has came from. 

If they hit a PE service it gas will escape. Only at a pressure of about 28mb…not a great deal. To stop it, it will be squeezed off 2 fusion sockets put on and then reinstated. Not a difficult job by any means. 

MouldyOldDough

My supply is via a flexible yellow "hosepipe" is this normal? 

grumbler

Yes