Natural Gas Shut Off

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After I had my house built, I noticed that the natural gas line to the dryer did not have a shutoff valve. The builder sent over a plumber to install one. Without turning off the gas, he unscrewed the end cap, doped up the threads, and screwed in a shutoff valve. Although it only took less than a minute, was this safe? This was located in the basement near the furnace and water heater, which could have provided an ignition point. I never had to shut off the gas to the whole house. For my information, where is the main shutoff for the gas?
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mainm shutoff should be at meter.
yes its safe provided its completed fast. just like working with live electric lines, that safe too if done properly.
natural gas is lighter than air, and the amount lost small. so dont worry
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On Mon, 3 Dec 2007 08:08:03 -0800 (PST), " snipped-for-privacy@aol.com"

See
http://www.gru.com/stormcentral/images/valve.gif

Recently the gas company was out to put a new meter on a new home. She installed the meter and opened a gas line inside the garage to purge the line. About thirty feet away was a lit cigarette.
The tech told me that the cigarette was "not hot enough" to ignite the gas. I was surprised by this comment.
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A smouldering cigarette isn't very hot - puffing it makes it a lot hotter, and apparently methane has a rather high ignition energy compared to other gasses.
However, the explanation is probably not that.
Methane has a LFL (lower flammability limit) of 5.3% and a UFL (upper flammability limit) of 15%. It also has LEL (lower explosive limit) of 5.53%.
Which means that unless the methane concentration in air is between LFL and UFL, it won't ignite.
Gas lines past the regulator are also fairly low pressure, so opening it doesn't spew gas very quickly. Secondly, methane is lighter than air, so it goes up, rather than stick around.
An residential gas line venting in open air, is quite unlikely to ignite from something 30' away. Even enclosed in an open garage, it'd take a while to build up the concentration to the danger point - if there's any ventilation at all, it might not ever reach that concentration more than a few feet away from the vent point.
You still have to be careful - there could be wind patterns that push a plume to exactly the right place. And it depends on the gas. Propane is heavier than air. It will "puddle" in depressions and stick around for quite a while in low wind conditions. There was a propane tank car derailment around 40 years ago in the north end of Toronto, where the tank fully vented. Everything was pretty much under control, until the propane flowing down a small creek valley (very still air conditions) finally reached an open flame about half a mile away.
Can't happen with methane.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
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On Mon, 03 Dec 2007 18:31:27 -0000, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

Thanks. IIRC, she did state that striking a match would be hot enough to ignite the gas, but the concentration would have to build up.
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Oren wrote:

Methane's is far below zero and a cigarette or match would readily ignite it. Static electricity, like from walking over a nylon carpet could ignite it. There is also autoignition temperature and it takes a very hot surface to ignite methane. The tech's comment about the cigarette was downright stupid.
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On Mon, 03 Dec 2007 15:02:31 -0500, Frank

The very reason I jumped! Then questioned her. I think she was hot for a girl on site :)
But I don't know.
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What's stupid about it? It was the truth.
s
The tech's comment about the

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Not quite. Flash point is the point at which a liquified gas can produce enough vapor to flash when ignited with a flame. By definition, methane in a home is well above flash - all flammable gasses are above flash point when they're a gas. The issue raised by the OP was the temperature of the ignition point.

The autoignition temperature of methane is 537C. Which theoretically means that methane won't ignite unless it comes in contact with something above 537C.

http://www.physlink.com/Education/AskExperts/ae1.cfm http://www.nature.com/nature/journal/v247/n5440/abs/247405a0.html
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
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On Dec 3, 12:31 pm, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

I have been told that natural gas is not chemically pure. It is a mixture of various natural gases - methane, ethane, etc. What the utility company does to ensure a uniform BTU, I don't know.
As for the low pressure of the gas line, I know that I have turned on the gas at a stove where it did not ignite immediately. The gas buildup from just waiting a couple of seconds before finally igniting produces a mini explosion that would singed my eyebrows if I were close enough. A plumber's face would be closer to an open pipe. I guess a good plumber will still have hair on his face.
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stove burners are mixers too, designed to mix air and gas for good burning. thats not the case with a open gas line.
gas companies do it all the time, as proof whens the last time your gas was shut off when they did repairs?
never in my case, really only occurs when water gets into gas lines. other than that gas up time must be 100%
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For what it's worth, I was watching TOH a few weeks ago where they tapped into the gas main to run a new line to a customer. They used something very similiar to those needle valves you use to tap into a water line. It was more sophisticated in that they drilled the line first and then attached the valve, but the device they used kept the gas line sealed at all times. I know that's not a repair, but the point is that they kept the system both pressurized and sealed at all times.
However, I do have a question about your repair scenario: If they actually opened the lines and vented the gas to the open air during a repair, wouldn't there be a "gap" in any downstream gas delivery that would extinguish any pilot lights that were burning?
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DerbyDad03 wrote:

That was the new service line to the residence that was being purged, not the main, so the answer is "no", they wouldn't have noticed.
As for the tap-in, sure they seal and are careful of sparks, too, but the main lines are at much higher pressure/volume than a single service line so they lose much more gas than the scenario here.
--


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If you were responding to my post, you may have misunderstood my question snipped-for-privacy@aol.com...
I was asking about his repair scenario, not the new service line to the customer.
hallerb said "gas companies do it all the time, as proof whens the last time your gas was shut off when they did repairs?"
I am assuming he means that the gas company does not shut off the gas every time they repair a gas line. Here's my question: If they open a line and vent it to the air during the repair, then wouldn't any downstream customers lose pressure and therefore lose their pilot lights? I'm not questioning the fact that they do or don't shut off the gas, but it seems to me that to any customers downstream of the repair, it's going to look like the gas was off if they open the line.
Perhaps they tap around the repair before opening the line? If that's the case, no one would lose service, but they are not really doing the same thing as a guy installing a valve or T in a house like the OP (and I) have seen them do.
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DerbyDad03 wrote:

OK, yes, I did misread your question and answered the unasked one... :)
If they were, indeed to completely open a line, then yes, unless there were alternate supply there would be a loss of service downstream. IME anything that required that level of work _would_ entail a notification and a cessation of services. Not many residential branches have alternate supply mains although I suppose if the work were extensive enough they might bypass an area to not have extended outage.
In general, installed pipelines are pretty maintenance free for quite long time periods so the consumer observation of loss of service is quite rare. Our tap comes directly off a main (36") cross-country line that crosses our place east of the house about a quarter mile away. To the best of my knowledge that line hasn't had a service outage in 20-something years since they redid a section. It is flown by aerial surveillance once/month to spot any problems. The other line just to the west of the house that was more recently laid was worked on just last year to lower it under the road because the county has been making noises of re-elevating these roads sometime and if they were to do so they just might have come close to the existing depth. It's a 42" line and was shutdown for a period while the new section was fitted in and welded in place. They only dug access holes to the ends on each end about 40-ft away from the road and then a little longer trench on one side. The then punched the new through under the road w/o trenching the 100-ft or so from one access hole to the other. The did a local pressure test on the new section before inserting it then a pressure test on the last connections and done. On those big lines they don't/can't flush them anyway because of the length the amount of air in a 100-ft section out of the 1500 miles before it gets to its ultimate destination is inconsequential as it gets mixed up during the compressor booster stations anyway.
For smaller side distribution lines I don't know whether they would bother to try to purge or not or whether they just let the end users deal with it until the air slug is gone...
--
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Oren wrote:

A lit cigarette won't ignite gasoline either.
A lit cigarette is barely hot enough to ignite another cigarette.
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Said to be demonstrated, by tossing a lit butt into a open container of gasoline. Supposedly, it will be distinguished.

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re: Supposedly, it will be distinguished (sic)
Distinguished or extinguished?
Distinguished might certainly fit the situation if it blew up.. ;-)
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On Mon, 3 Dec 2007 14:42:02 -0800 (PST), DerbyDad03

You are correct:(
EX vs DIS
-- Oren
"Well, it doesn't happen all the time, but when it happens, it happens constantly."
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Gasoline does not 'blow up'.
s
wrote:

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