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Old 10-14-2009, 11:42 PM   #1
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Very slow gas leak is okay


I'm interviewing plumbers for a gas line extension and had a nice long conversation with this seemingly VERY experienced, very knowledgeable, very skilled, state-licensed, totally no-nonsense guy who seemingly has no reason to bullsh*t me about the dangers of gas leaks.

Bottom line is that he thinks a very slow gas leak, for example an overnight drop of 5 psi when pressure tested at 15 psi, which is required to hold for just 10 minutes for the inspector, is okay. He's said that it would be safe enough, and regardless of location, whether it's behind the range, inside a cooktop cabinet in the kitchen... or underfloor.

He says furthermore that high pressure testing is damaging to the pipe system, which makes some sense. In our area natural gas comes in at between 2 and 5 psi, and he says gas does NOT leak much at those low pressures.

The thought is just annoying to me.

This flies against common sense — that having ANY GAS LEAK is downright dangerous. But on the other hand, there's also some sense in having a tolerance of acceptability. The code requirement for testing must be so lax for a reason. Who can be so perfect.

So what's your take (and what's your professional background)?


Last edited by KCnorthernCA; 10-14-2009 at 11:49 PM.
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Old 10-15-2009, 09:12 AM   #2
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Very slow gas leak is okay


No professional background.

I would say that any measurable leak in the interior of the house needs to be fixed before the system is put in operation.

Depending on how well sealed the interior of the house is (for energy efficiency) and how long the gas has gone on leaking, you can build up a mixture of gas and air that is explosive.

Pilot lights in water heaters and furnaces have an interlock based on a thermocouple to stop the pilot light gas feed and prevent gas from accumulating in the house if the pilot light was accidentally extinguished.

If the main gas shutoff were turned to "off" and pipes were disconnected and worked on, then the gas already in the pipes and allowed to escape would probably not be enough to cause an explosion. But if there were a small leak enough to let the pressure drop from 5 psi to 2 psi while you were out, the pressure won't really drop to 2 psi but would rather be replenished with more gas from the main, and over a period of hours you could get an explosive mixture.

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Old 10-15-2009, 09:22 AM   #3
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Very slow gas leak is okay


No background either....but

Quote:
My house didnít explode into flames; my family didnít asphyxiate in their sleep, nothing as dramatic as that. No, our leak was slow and undetectable to ourselves and visitors to our home. We lived in our house for nearly 4 years before we discovered what was making us all sick. Very sick.
My family developed several medical conditions as a result of our exposure. No one was left untouched by the exposure, even our pets.
http://www.gas-leak.org/

http://www.homelandnaturalgas.com/Vi...Poisoning.html
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Old 10-15-2009, 10:47 AM   #4
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Very slow gas leak is okay


Background-Jack of some trades

NY Times has a page one article today(read it online) that says natural gas leaks are a major cause of global warming equivalent to half of coal fired generating plants. They are talking about leaks at the well head, and major transmission lines and storage tanks.
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Old 10-15-2009, 12:20 PM   #5
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Very slow gas leak is okay


All comments so far are appreciated, but you're still describing only the dangers of an obvious gas leak.

The topic here in essence is about the level of acceptability.

Sure we can all cry our faces blue over any absolute black and white simple nothing issue before us in written words in theory. But just as the FDA allows a *MINIMUM* number of rodents in large food storage silos and not an absolute antiseptic requirement (that's why you find at least one rodent hair in every box of cereal you buy), the real world of production and practice is starkly different.

So if this is turned into a poll, the poll would be two-part reading something like:

Part 1
What would you do if your gas pipes tested to pass inspection (holding 15 psi for 10 minutes), but you decided to leave the pressure gauge connected overnight only to notice a slow drop to 10 psi next morning?

A. You look the other way. It's fine. No problem
B. You lose sleep but you can't do anything. It's code compliant
C. You complain but the plumber and the inspector laugh at you
D. You insist on having it fixed but the plumber can't find the leak
E. You suggest high pressure testing, but plumber balks
F. You do your own high pressure testing whatever
G. You buy more property insurance

Part 2
What level of leak would satisfy you?
A. 10 psi holding for 15 minutes as long as the needle gauge looks fairly still
B. 15 psi holding for 10 minutes with no noticeable needle movement
C. 15 psi must hold for 1 hour, needle can drop slowly after that
D. 15 psi must hold for 24 hours
D. 15 psi must hold forever, like weeks and months and years
E. 60 psi must hold forever

Last edited by KCnorthernCA; 10-15-2009 at 12:21 PM. Reason: spelling correction
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Old 10-15-2009, 05:44 PM   #6
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Very slow gas leak is okay


I would want the normal testing pressure to hold for 24 hours or such greater time as code specifies. If it doesn't I would want the installing plumber to make a good faith effort to find and fix any additional leaks after which I will accept passing code, which should be factual and cut and dry but if not, passing code in my opinion (as opposed to the plumber's opinion).
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Last edited by AllanJ; 10-15-2009 at 05:46 PM.
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Old 10-15-2009, 06:43 PM   #7
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Very slow gas leak is okay


I agree with the plumber and I disagree and this is why

1. Most codes require a testing of 20 psi for 30 minutes (At least mine does and if you are under the International or Uniform Plumbing Code this is the requirement) This is a fairly common time/pressure. I have never heard of a testing pressure of 10 or 15 and it has always been 30 mins.

2. The gas pressure entering the house after testing is MUCH less than testing pressure. If you are natural gas the pressure is reduced to 9-10 Inch Water Column and LPG 11-12.

Now what does that mean well 1 psi is equal to 27.68 in wc. So at 9 or 10 in wc you are less than one half of one psi entering your house for gas service. So a VERY VERY VERY small leak most likely will not be found. Sometimes a very small leak will need a higher pressure to reveal it to the plumber or home owner for repair.

As far as Scuba Dave situation (IMO) had a larger leak which required a high pressure to be found and when the system is pressure tested at 20 psi for 30 mins, it would fail the test, thus needing a repair

Almost all gas lines have a small leak and will fail the test going 24 hrs. These systems are not hermitically seal but thread and thread seal tightened.

I personnally will set the pressure on a pressure test and run the 30 mins and go look at the gauge, if no movement then go another 30 mins, if a leak I will spray all fitting joints with soapy water mix and check for bubbles and then make repairs and then retest.

Keep in mind that you gas pressure will and should never be at the same pressure used for testing and if it does you will know it. Furnace will act up, water heaters could over heat and so on.

Hope this helps
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Last edited by Plumber101; 10-15-2009 at 06:47 PM.
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Old 10-15-2009, 09:24 PM   #8
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Very slow gas leak is okay


Quote:
Originally Posted by zircon View Post
Background-Jack of some trades

NY Times has a page one article today(read it online) that says natural gas leaks are a major cause of global warming equivalent to half of coal fired generating plants. They are talking about leaks at the well head, and major transmission lines and storage tanks.
since this is not a blog about Politics, I will not give my opinion of the New York Times, but we are concerned about the short/er term effects of a gas leak (small as it may be) on health and safety. The point of the OP was. That they were astonished to hear a so-called "licensed and accredited professional" make such a statement. As all the posters have pointed out, the Negative effects of Natural Gas leaks are very real, on both, health and safety. Eliminate confusion Through Education! Don't Drink and Drive, Ever!!!
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Old 10-16-2009, 09:18 AM   #9
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Very slow gas leak is okay


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What would I want? I'd want there to be zero leakage in my gas system. Not a little, not a tiny amount, but zero. However... I don't live on Planet Pretend, I live here. And here there are things called engineering tolerances. There's the reality that not every fitting will seat exactly perfectly. Not every thread is machined to perfection. The fact that we use pipe dope or (yellow) Teflon tape on the threads shows that.

The code calls for 20 psi for 30 minutes. Would I like to see 20 psi for maybe an hour? Sure. But at some point it's not a perfect system, and it will leak. A 5 psi drop overnight? Not sure. Define overnight. Hookup at noon, comeback at noon? 5 psi over 24 hours at 40 times the pressure of the gas that will be in the system? I would probably be ok with that. That of course assumes there wasn't a drop in psi over 30 minutes.
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Old 10-16-2009, 01:37 PM   #10
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Very slow gas leak is okay


Quote:
Originally Posted by WaldenL View Post
Level of experience: DIYer

What would I want? I'd want there to be zero leakage in my gas system. Not a little, not a tiny amount, but zero. However... I don't live on Planet Pretend, I live here. And here there are things called engineering tolerances. There's the reality that not every fitting will seat exactly perfectly. Not every thread is machined to perfection. The fact that we use pipe dope or (yellow) Teflon tape on the threads shows that.

The code calls for 20 psi for 30 minutes. Would I like to see 20 psi for maybe an hour? Sure. But at some point it's not a perfect system, and it will leak. A 5 psi drop overnight? Not sure. Define overnight. Hookup at noon, comeback at noon? 5 psi over 24 hours at 40 times the pressure of the gas that will be in the system? I would probably be ok with that. That of course assumes there wasn't a drop in psi over 30 minutes.
Your points are 100% on target. There are engineering data on the permeation (and dissipation) of gas in the air that we breathe (measured in ppm. & ppb.) and the tolerances of joints and seals. But for a professional to tell a lay person that "A little bit of gas won't kill you" sounds horrible. We really strive for zero tolerance. But since that is impossible we're satisfied if it's up to code. Eliminate confusion Through Education;
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Old 10-16-2009, 02:25 PM   #11
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Very slow gas leak is okay


There must also be an assumption in these numbers that no house is airtight or that doors or windows will eventually be opened.
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Old 10-16-2009, 05:27 PM   #12
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Originally Posted by Yoyizit View Post
There must also be an assumption in these numbers that no house is airtight or that doors or windows will eventually be opened.
At the worst they'll be opened by the police when they come to take our your dead asphyxiated body.
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Old 10-17-2009, 07:06 AM   #13
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Very slow gas leak is okay


Here we test gas lines at 30psi for 30 minutes although I usually put it on test and leave it until inspection....which could take up to 3 days. The inspections are done by our local gas/electic provider, Duke Energy. When they inspect, they put their own testing device on the system. They use a Kohlman gauge (may have the spelling wrong on that) that is ultra sensitive. If it passes their own test then I'm good with it.
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Old 10-17-2009, 09:43 AM   #14
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Very slow gas leak is okay


Methane (natural gas) per se is not listed as a toxic gas. Like all simple asphixants (carbon dioxide, nitrogen for example) it displaces oxygen from the air, and if the oxygen level gets low enough, you die from lack of oxygen.

However, the lower explosive limit for methan is 5%, and the upper explosive limit is 15%, so you are likely to blow up your house long before the concentration of methane reaches a level capable of asphyxiating you.

That said, all methane distributed in the United States is odorized with a chemical like thiophane that is designed to warn occupants when there has been a leak. Thiophane is the familiar "rotten egg" odor of natural gas. Pure methane has no odor so far as I know, which is why the thiophane is added. According to an article on odorization I found at http://unece.org/trans/doc/2008/wp29grsp/SGS-2-04e.pdf
the standard is for a human to be able to detect a natural gas leak at 1 percent methane concentration, which is 5 times below the lower explosive limit.

None of this answers the simple question about how dangerous it is if the pressure drop test passes, but there is still a slow leak. I do not have natural gas in my house, however if I did, I would purchase a couple of methane detectors (similar to carbon monoxide detectors) and place them strategically in the house, probably one in the kitchen and one in the hallway. My concern would be that over time, a leak could develop in the pipes that was not present during initial installation. My guess is that like electrical wiring, once installed gas lines are not routinely checked, and like electrical lines they are subject to slow deterioration, especially at the valves, hence could potentially develop leaks after several years of service. The detector would not identify the source of the leak, but would at least warn the occupants that there is a hazard, and allow them to get the source of the leak located and fixed.
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Old 10-17-2009, 08:40 PM   #15
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Very slow gas leak is okay


Daniel Holzman (civil Engineer) (Post #14) I did not post your quote because I don't know (yet) how to fractionalize a quote and the entire piece would take up too much space.)
You make some strong (theoretical) points. But when the standard is 30 psi for 30 Min. and the system passes that test, then any gas that (still) leaks is not "negligible" but hypothetical. Furthermore, no house is hermetically sealed. Doors and windows are eventually opened. And if a significant leak develops in time, there is always the Odorization that ALL the utilities are adding, to alert people.
p.s.: In NYC, Gas inspections are done by City Inspectors, who are all former tradesmen, who spent most of their adult life working in that trade, as are Electrical Inspectors.As opposed to some smaller Municipalities who employ "Multi-Service" Inspectors, which is not as high a standard as lifetime specialized professionals. Eliminate confusion Through Education; Don't Drink and Drive, Ever!!!

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