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Thread: PG&E gas explosion San Bruno CA 9/9/10

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    Senior Member wet_boots101's Avatar
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    Default PG&E gas explosion San Bruno CA 9/9/10

    http://www.sfgate.com/cgi-bin/articl...BJRS.DTL&tsp=1
    ca_gasfire.jpg
    Saw this tonight before going to bed... anyone in the know?

    Unconfirmed natural gas explosion, no details as to cause. Sure sounds like a dig-in or major malfunction of some sort though.
    "Aye, verily hath I spoken." - Thor, god of thunder

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    Senior Member The Big-E's Avatar
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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Last news I saw this morning on ABC news was that it was a 24" Transmission Main!!!! Yikes...

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    I was watching the news this morning and their really isn't any info yet, other then it being a 24" transmission line. The lat report I saw was 6 dead and over 50houses demolished.

    The local news interviewed a "neighbor" that stated the neighborhood has complained of a gas leak for the past 3 weeks..... sounds hokie to me

    mke

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Quote Originally Posted by Mke View Post
    I was watching the news this morning and their really isn't any info yet, other then it being a 24" transmission line. The lat report I saw was 6 dead and over 50houses demolished.

    The local news interviewed a "neighbor" that stated the neighborhood has complained of a gas leak for the past 3 weeks..... sounds hokie to me

    mke
    Not impossible. I know that about 6 years ago Washington Gas Light had a backlog of gas leaks that was at least six months behind. Some one in some office decides they want to make their monthly, quarterly or whatever time period numbers look better and they reduce the scheduled number of repair jobs. WGL got caught up after a house exploded on one of those old leaks.

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    this is going to be interesting to say the least!!!
    wise men talk because they have something to say and fools because they have to say something....plato

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    Mke
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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    hey PL, I agree with you, and have seen similar in this area, however this is a transmission line, not a 4" poly feeding a subdivision. The more I think about it, I think I'm holding the gas company to higher standards that I have seen Practiced by Northwest Natural Gas. There is another company up here that does not follow the same safety plans that NNG has. This other company has a catastrophic failure about once every 3-4 years. One about 10 yrs back killed a couple of boys near seattle. http://www.ntsb.gov/publictn/2002/PAR0202.htm

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    Senior Member Bad Robot's Avatar
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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    This appears to indeed be a transmission line, but according to this it was a 30". Please say a prayer for these folks, and for those investigating this tragedy.

    http://gantdaily.com/2010/09/11/hund...gas-explosion/

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Yeah, still doesn't say anything as to cause yet. Possibly: the gas people smelled was not service leaks, but the big P/L slowly letting loose?

    Also, what would ignite it? Which is why I originally brought this up. Digging + careless contractor + no marks = gas explosion ~? If it was near the back yards of nearby homes, and someone was doing extensive landscaping work... even digging a sewer cutout or something mundane? That could do it.
    "Aye, verily hath I spoken." - Thor, god of thunder

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Wouldnt it be possible for a small leak to build up a large amount of trapped gas , depending on the soil type and layers etc ? It would be leaking out to the surface here and there of course.. maybe what the ppl were smelling.
    Do you get tolerant of that gas smell after you've been exposed for a while ?

    Ive always been kind of shocked when I see the gas guys searching for a leak up here. They hammer a steel rod down into the earth and then stick a probe into the hole to check the gas levels. When they get a peak reading, they dig it up there.
    I always wondered, couldnt a spark from the rod hitting a rock/etc light the gas ? Maybe there's not enough oxygen at that point..
    (May you live in interesting times)

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Quote Originally Posted by Dave72 View Post
    Wouldnt it be possible for a small leak to build up a large amount of trapped gas , depending on the soil type and layers etc ? It would be leaking out to the surface here and there of course.. maybe what the ppl were smelling.
    Do you get tolerant of that gas smell after you've been exposed for a while ?

    Ive always been kind of shocked when I see the gas guys searching for a leak up here. They hammer a steel rod down into the earth and then stick a probe into the hole to check the gas levels. When they get a peak reading, they dig it up there.
    I always wondered, couldnt a spark from the rod hitting a rock/etc light the gas ? Maybe there's not enough oxygen at that point..
    It is not that you get used to the smell of the gas, it is that the smell, which is added to the gas, can be filtered out by the earth when the leak is slow.

    The explosion in question was on a 30" line suggesting a high pressure transmission line. These lines run from about 240 psi to over a 1,000 psi. A small ding in the pipe will form a weak point and after several years of constant high pressure the pipe will burst at the damage point. When a pipe like this ruptures it can split open as the pressure causes the small hole to expand and the pipe will split open over a large area. Now a large amount of high pressure gas is rapidly released and the first thing it does is form a pressure dome of dirt. This pressure dome will not last long, maybe a second or less and then the high pressure gas pocket will cause the earth to blow skyward forming a crater. You now have a large cloud of flammable gas in the air being fed by a burst pipe. Any nearby ignition point can set of the gas cloud but a common ignition source is a static electric charge created by the flowing gas. The gas ignites rapidly and goes off in an air burst like a fuel / air bomb and the pressure wave can flatten houses or knock them off their foundations.

    You are right, trapped under the earth there is not enough oxygen for the gas to ignite so looking for it by hammering rods into the ground offers minimal risk. Natural gas ignites only in a narrow band of gas to air percentage. Too low a percentage of gas and it does not ignite, too high a percentage of gas and there is not enough oxygen for it to ignite.

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Seriously PL, you should be nicknamed "The Professor."

    I think all of us hit the nail on the head... a long quote from the latest I read was,

    "San Francisco-based D'Arcy and Harty Construction received a contract from San Bruno in 2008 to do sewer replacement work on a 1,600-foot stretch along Earl Avenue, work that would have occurred at the site of the explosion.

    Peter Knudson, spokesman for the NTSB, said his agency is looking into the history of the project. The work included replacing manholes and creating a new sewer on Earl between Sneath Lane and Glenview Drive. The natural gas pipe blew at the intersection of Earl and Glenview.

    The NTSB has asked for records of the sewer project as part of their wide-ranging investigation into possible causes of the explosion, Knudson said."
    Read more at http://www.sfgate.com/cgi-bin/articl...BAEP1FCNS9.DTL
    "Aye, verily hath I spoken." - Thor, god of thunder

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Quote Originally Posted by wet_boots101 View Post
    Seriously PL, you should be nicknamed "The Professor."

    I think all of us hit the nail on the head... a long quote from the latest I read was,

    "San Francisco-based D'Arcy and Harty Construction received a contract from San Bruno in 2008 to do sewer replacement work on a 1,600-foot stretch along Earl Avenue, work that would have occurred at the site of the explosion.

    Peter Knudson, spokesman for the NTSB, said his agency is looking into the history of the project. The work included replacing manholes and creating a new sewer on Earl between Sneath Lane and Glenview Drive. The natural gas pipe blew at the intersection of Earl and Glenview.

    The NTSB has asked for records of the sewer project as part of their wide-ranging investigation into possible causes of the explosion, Knudson said."
    Read more at http://www.sfgate.com/cgi-bin/articl...BAEP1FCNS9.DTL
    In this link http://www.csmonitor.com/USA/2010/09...investigate-it there is a photo of the crater. the right shape and more then big enough to drop a city bus into and have room to spare. From the shape of the crater the pipe failed at some point and then the high pressure gas force the pipe to split apart down it's length. The crater was not caused by the gas igniting, that came later after it was released into the air and found an ignition source. The crater was in all portability caused by the pressure of the escaping gas.

    Gas is considered an interstate transport product and the pipelines are regulated buy the Federal DOT. They do not allow any structure to be built within so many feet of the right of way itself. I used to know the number of feet but have forgotten. This interstate transport under federal regulation is why all locators who mark gas are required to take mandatory DOT drug tests even if it is not a standard requirement of your locate firm.

    How these pipelines are built in urban areas or such building allowed to be built around them is a mystery to me.

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    About 3 years ago a company built a new 200 unit apt complex right on top of a 16' high pressure transmission line in my area. There are only 2 1'x1' signs at each end of property where it comes in and goes out. I have always wondered if the prospective tenants are told about this line?
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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    if this was a high pressure line it wouldn't have odorant added yet would it. I know in my part of the world it gets added at the tbs where the pressure is dropped to around 90 psi. I once asked a gas guy why no odorant was added to the high pressure stuff and he said you see e m before you smell em. The high pressure lines that feed our town come in at 500 to 800 psi but are only 12 inch lines.

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    Default Re: PG&E gas explosion San Bruno CA 9/9/10

    Quote Originally Posted by sprayandpray View Post
    About 3 years ago a company built a new 200 unit apt complex right on top of a 16' high pressure transmission line in my area. There are only 2 1'x1' signs at each end of property where it comes in and goes out. I have always wondered if the prospective tenants are told about this line?
    I had a ticket recently for the local park department, they where digging up the base of the playground equipment at this little park in town. The prints showed that there was a 8" transmission main running down the same side of the road as the park. I thought that was a little crazy since the playground was only about 20' off of the road. I hooked to the test stand down the road and started to do my sweep in the ROW and could not find the main. After scratching my head for a minute I started to walk towards the playground thinking there is no way in the world it would be off the road that far. Well I was wrong the main laid about 3' off of the base of the playground equipment. There is no doubt in my mind that somebody was a complete retard for putting the playground there, its bad enough they built one so close to the road but to have it right on top of a transmission gas main is just plain stupid. I painted and flagged the shit out of the main so that way any parent who brought there kids there to play will know its there. It just goes to show that some people refuse to put the safty of others first.

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