Permissible drop and TT

[Leo21]

Better to ask customer if they ever smell gas before you start any work.
They will say no if its true.
The second your looking for a leak they miraculously can smell gas and walk round the house sniffing like a dog.

So true, anyway it's 4 mbar isn't it?

 

[Leo21]

For me the grey area is the fact that the carcuss can't be leaking, but how do you know unless you isolate appliances?

 

[johnnyplumb]

5.4 NEW EXTENSIONS/ALTERATIONS TO EXISTING INSTALLATIONS
Before commencing the new work, the existing installation shall be tightness tested in accordance with clause 5.3.2 and any permissible pressure drop over the 2 minute test period noted (see also Sub-Section 4.2).
Upon completion of the work to the existing system, the tightness test shall be repeated and the pressure loss after the 2 minute test period shall be no greater than that previously measured and there shall be no smell of gas.

You only "need" to do what you "need" to do. Whether you choose to work above the requirements is up to you and perhaps your wallet or conscience.

Put the scenario into a bit perspective here and think about it. How much gas would be released from a 2mb drop?
Cleverer people than us do some fancy sums and decide what would be safe or not safe. When they come up with what they think is a safe figure, we are talking really safe. Not about half of what would cause the house to blow up. We are talking many many times more on the safe side.

Since i don't need to get up in the morning and there is nothing worth watching on the telly, here is a sum (or calculation if you like that word better) that shows the amount of gas that would be released into a room with a 2mb drop.
The formula for working this out is
LR (leakage rate) = F3 (some clever people worked that out and it is a constant for the type of fuel) X GM (gauge movement) X IV (installation volume) ÷ TTD (tightness test duration)
stick some numbers in and
LR = 0.059 (a constant number for ng) X 2 (the gauge dropped 2mb) x 0.02 (a guess on the big side on this one) ÷ 2 (test time)
LR = 0.00236 ÷ 2 = 0.00118m³/hr


Now think of the EL's of ng, volume of any small space a pipe is allowed to pass through without being vented and think about the number of air changes that occur in an average domestic space.

I know how i would treat this (providing there "IS" no smell) without blinking an eye this but i know how to do fancy sums too and so do you now if you remember it.

Maybe this should be moved to the gsr section

It's not just the gas released you haveto worry about.
There's another safety critical issuethat might cause a problem,


The clever people that do the fancysums your talking about, are not as clever as they would have usbelieve :disappointed:


all will be revealed later :hurray:

 

[Mike Jackson]

For me the grey area is the fact that the carcuss can't be leaking, but how do you know unless you isolate appliances?

But the carcass can be leaking if there are appliances connected. The inference from IGEM-UP-1B Ed3 is that the carcass can't be leaking but nowhere does it say that.

 

[Keefy]

It's not just the gas released you haveto worry about.
There's another safety critical issuethat might cause a problem,


The clever people that do the fancysums your talking about, are not as clever as they would have usbelieve :disappointed:


all will be revealed later :hurray:

Oven bypass flame?

 

[kirkgas]

You are not allowed any drop on pipework all appliances have service valves or should have.

We all know you can't have a known leak on pipework, what the relevance of service valves?

 

[Keefy]

We all know you can't have a known leak on pipework, what the relevance of service valves?

You have a point there, now I'm confused. Is a drop allowed on existing pipework [with appliances fitted] or not?

 

[Billy Bob Bob]

We all know you can't have a known leak on pipework, what the relevance of service valves?

quick isolation,unless there passing

 

[kirkgas]

There's lots of talk of what the book says and what trainers have said but how many answering the original question have

1. Read the original question properly and

2. Read IGEM-UP-1B Ed3

The question is what is the legal requirement, not best practice or what your Auntie Hilda says.

The actual wording of the relevant paragraphs is



The inference is that the drop must be through an appliance but nowhere does it state that you need to prove this. It may be good practice to go beyond the legal requirement but you could be landing yourself in hot water by doing so. Suppose you carry out a LL check and find a 3 mbar drop. Being the concientious engineer that you are you go round and isolate all of the appliances and the drop is still there. You are now legally obliged to rectify the leak or make it safe. Unabgle to find the leak you disc the meter and leave the tenant with no heating, hot water or cooking facilities. The landlord goes ape and sues you. You may feel that you were doing the right thing but, legally, you have exceeded the legal requirement.

The correct method of dealing with the situation is to ask the tenant if they have noticed a smell of gas within the property and then proceed further if they say yes. 9 times out of 10 the tenant will reply in the affirmative and that is when you start isolating stuff to locate the source of the leak.

Before getting to this stage I'll normally give the meter unions a quick tweak as I find most small drops are slight weeps on the meter unions or at the outlet of the ECV.

Mike, the best reply yet, ( because you agreed with me hahaha)
Seriously the scenario you gave is EXACTLY the scenario I use with students, I always start by demanding they tell me the exact requirement under regs, I have no interest in what they want to do above that, until we speak to the customer or client etc
And I have no interest in what they believe is better practice, the question is what MUST be done

 

[kirkgas]

You have a point there, now I'm confused. Is a drop allowed on existing pipework [with appliances fitted] or not?

Not if you KNOW its on the pipework, haha I'm really glad I started this thread

 

[Keefy]

Not if you KNOW its on the pipework, haha I'm really glad I started this thread

**** this I'm gonna blow the dust off my GSIUR book and have a read.

 

[kirkgas]

**** this I'm gonna blow the dust off my GSIUR book and have a read.

You would be better looking in the IGE/UP/1b

 

[Keefy]

You would be better looking in the IGE/UP/1b

But I've only got this one.

 

[kirkgas]

But I've only got this one.

View attachment 13326

That's even worse cause its the old one, get on the GSR website and download the newer version

 

[Keefy]

That's even worse cause its the old one, get on the GSR website and download the newer version

I'm not actually looking to do gas again, at least not for the forseeable future but I do like to try and keep up with the latest. I'll take a look, cheers. 🙂

 

[Howsie]

It passes.

 

[stoker122]

It's a pass, no reason to suspect its not an appliance.

 

[mfgs]

There is no obligation to try and find the leak or confirm its not on the pipework. The moment you start looking for it, you tie yourself up in regulations and will end up capping people off. I personally don't investigate if the drop is within limits unless there is a reported smell or I can smell gas.

What puzzles me is surely if people go around isolating appliances to make sure the leak isn't on the carcass are they then happy to leave the appliances connected knowing they are leaking? A boiler with a gas valve letting by surely needs action taken? Its a failed safety device after all.

 

[kirkgas]

Mfgs
You make a valid point, I leave the 2mb drop every time, as you say the next guy shuts all the appliances then confirms one of them is leaking, so he puts the boiler then cooker back in still no drop, he then opens the fire pedestal to find the 2 mb drop, as its on an existing appliance he leaves it, but where is it dropping 2 mob between the ped and inlet side of the control valve
I love this thread

 

[Leo21]

What's with the 2mbar drop, last time Iooked at a book it was 4mbar. Or 16/10ths in old money.