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  1. #1
    sam sanders's Avatar
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    Default Gas line under slab

    I call out Gas lines being buried under an exterior slab (without properly vented conduit), but when people ask how serious a problem this is, I have a hard time coming up with an answer. I know there could be a leak under the slab, but there is only around two pounds of pressure in the gas line, it seems unlikely gas would force it's way out if it was surrounded by compacted soil or in concrete. If it did manage to get out and even form a pocket underground, it would eventually find it's way through the slab, and being outside, is this a real danger when tiny amounts of gas percolate through a slab and diffuse into the atmosphere? I know I'm missing something, but I really can't figure it out.
    I would be thankful for anyone's help,
    Sam

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  2. #2
    chris mcintyre's Avatar
    chris mcintyre Guest

    Default Re: Gas line under slab

    Quote Originally Posted by sam sanders View Post
    I know there could be a leak under the slab, but there is only around two pounds of pressure in the gas line...
    In my area I don't believe I have ever seen a gas line under slab, why would you run a gas line under the slab? Is there an advantage?

    Pressure on gas lines is around .25 psi, unless of course it is a 2 lb. system.

    Sorry I couldn't be of any help Sam, but I did want to throw the other question into the mix.


  3. #3
    Join Date
    Mar 2007
    Location
    Plano, Texas
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    Default Re: Gas line under slab

    Have you ever seen a house explode because of a natural gas leak?
    It ain't pretty.
    The gas leaks out under the slab for weeks, months, years until one day it is channeled to just the right (or wrong) area at just the right concentration with one spark or open frame.
    As with most codes, there is a reason that they code was changed to prohibit a practice, usually because someone died.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  4. #4
    Join Date
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    Chicago, IL
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    2,797

    Default Re: Gas line under slab

    I read an account a while back of a natural gas explosion which leveled a house as a result a gas leak into the basement from a leak in either the supply to the meter or the line from the meter into the house (don't remember which, if the article mentioned it) and through the foundation wall (I assume at the pipe entry, but don't know that for a fact) - but in any case the leak was external to the foundation wall.

    I can easily imagine the same thing happening at a gas line leaving a structure and running under a slab, especially as something like a patio slab is often immediately adjacent the foundation, the gas line is often a retrofit passing through a oversize, unsealed opening in the foundation wall, in my area is often flexible copper, and is subject to damage for number of reasons, including a sinking slab.

    Last edited by Michael Thomas; 03-06-2010 at 06:39 AM.
    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  5. #5
    Mike Sims's Avatar
    Mike Sims Guest

    Default Re: Gas line under slab

    I am a Gas Safety Consultant. Several good points were made here, however I would like to add a couple more. IF code allowed a gas line under a slab or if someone just innocently poured concrete over a line to make a patio, drive way or sidewalk; these things happen. First if the gas line is old request the gas company come out and test the line for leakege. This is a quick easy test. Another test that can be done is Gas distribution system operators have a device called a CGI Combustible Gas Indicator (The only device that can give readings of concentration of Gas in air) to know how dangerous the concentration is "If it is near the Explosive level", and how to deal with it. I recommend everyone (Gas customer or not) get a Gas Detector and have it installed in the basement, crawl space, or what ever void is there; if the building was built on Slab find a location to put it. Gas like everything else follows the path of least resistance when it is released. Not generally a problem IF you can smell it. Some people for medical reasons or what ever cannot smell the odorant added to gas. Or as gas is migrating through the soil along its route of least resistance depending on humidity, soil conditions and distance migrated the odorant may have faded or been stripped right out of the gas making it un-detectable by smell. There are recorded instances where gas migrated through the soil and into a structure that did not even have gas supplied to it and the structure blew up! Visit us at www.lpgassafety.com


  6. #6
    Join Date
    Mar 2007
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    Plano, Texas
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    Default Re: Gas line under slab

    This is old but a good example of why laws and codes are changed. In this case, state odorization law for Texas.

    NEW LONDON SCHOOL EXPLOSION. In 1937 New London, Texas, in northwest Rusk County, had one of the richest rural school districts in the United States. Community residents in the East Texas oilfield were proud of the beautiful, modern, steel-framed, E-shaped school building. On March 18 students prepared for the next day's Interscholastic Meet in Henderson. At the gymnasium, the PTA met. At 3:05 P.M. Lemmie R. Butler, instructor of manual training, turned on a sanding machine in an area which, unknown to him, was filled with a mixture of gas and air. The switch ignited the mixture and carried the flame into a nearly closed space beneath the building, 253 feet long and fifty-six feet wide. Immediately the building seemed to lift in the air and then smashed to the ground. Walls collapsed. The roof fell in and buried its victims in a mass of brick, steel, and concrete debris. The explosion was heard four miles away, and it hurled a two-ton concrete slab 200 feet away, where it crushed a car.
    Fifteen minutes later, the news of the explosion had been relayed over telephone and Western Union lines. Frantic parents at the PTA meeting rushed to the school building. Community residents and roughnecks from the East Texas oilfield came with heavy-duty equipment. Within an hour Governor James Allred had sent the Texas Rangersqqv and highway patrol to aid the victims. Doctors and medical supplies came from Baylor Hospital and Scottish Rite Hospital for Crippled Children in Dallas and from Nacogdoches, Wichita Falls, and the United States Army Air Corps at Barksdale Field in Shreveport, Louisiana. They were assisted by deputy sheriffs from Overton, Henderson, and Kilgore, by the Boy Scouts, the American Legion, the American Red Cross, the Salvation Army, and volunteers from the Humble Oil Company, Gulf Pipe Line, Sinclair, and the International-Great Northern Railroad.
    Workers began digging through the rubble looking for victims. Floodlights were set up, and the rescue operation continued through the night as rain fell. Within seventeen hours all victims and debris had been taken from the site. Mother Francis Hospital in Tyler canceled its elaborate dedication ceremonies to take care of the injured. The Texas Funeral Directors sent twenty-five embalmers. Of the 500 students and forty teachers in the building, approximately 298 died. Some rescuers, students, and teachers needed psychiatric attention, and only about 130 students escaped serious injury. Those who died received individual caskets, individual graves, and religious services.
    Three days after the explosion, inquiries were held to determine the cause of the disaster. The state of Texas and the Bureau of Mines sent experts to the scene. Hearings were conducted. From these investigations, researchers learned that until January 18, 1937, the school had received its gas from the United Gas Company. To save gas expenses of $300 a month, plumbers, with the knowledge and approval of the school board and superintendent, had tapped a residue gas line of Parade Gasoline Company. School officials saw nothing wrong because the use of "green" or "wet" gas was a frequent money-saving practice for homes, schools, and churches in the oilfield. The researchers concluded that gas had escaped from a faulty connection and accumulated beneath the building. Green gas has no smell; no one knew it was accumulating beneath the building, although on other days there had been evidence of leaking gas. No school officials were found liable.
    These findings brought a hostile reaction from many parents. More than seventy lawsuits were filed for damages. Few cases came to trial, however, and those that did were dismissed by district judge Robert T. Brown for lack of evidence. Public pressure forced the resignation of the superintendent, who had lost a son in the explosion. The most important result of the disaster was the passage of a state odorization law, which required that distinctive malodorants be mixed in all gas for commercial and industrial use so that people could be warned by the smell. The thirty surviving seniors at New London finished their year in temporary buildings while a new school was built on nearly the same site. The builders focused primarily on safety and secondarily on their desire to inspire students to a higher education. A cenotaph of Texas pink granite, designed by Donald S. Nelson, architect, and Herring Coe, sculptor, was erected in front of the new school in 1939.
    BIBLIOGRAPHY: Lorine Zylks Bright, New London, 1937: The New London School Explosion (Wichita Falls, Texas: Nortex, 1977). R. L. Jackson, Living Lessons from the New London School Explosion (Nashville: Parthenon, 1938). U.S. Senate, Explosion at Consolidated School, New London, Texas (Document 56, 75th Cong., 1st sess., 1937).
    Irvin M. May, Jr.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  7. #7
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: Gas line under slab

    Quote Originally Posted by sam sanders View Post
    I call out Gas lines being buried under an exterior slab (without properly vented conduit), but when people ask how serious a problem this is, I have a hard time coming up with an answer. I know there could be a leak under the slab, but there is only around two pounds of pressure in the gas line, it seems unlikely gas would force it's way out if it was surrounded by compacted soil or in concrete. If it did manage to get out and even form a pocket underground, it would eventually find it's way through the slab, and being outside, is this a real danger when tiny amounts of gas percolate through a slab and diffuse into the atmosphere? I know I'm missing something, but I really can't figure it out.
    I would be thankful for anyone's help,
    Sam
    A place nick named electric city out by Stinnett Texas had gas lines running thru a neighborhood. They wound up moving and paying for countless homes due to the gas leaking into the homes and fires and explosions and asphyxiations. Yes, some of the homes were over the gas lines.

    Gas lines just running close to your home can leak in the soil and come up into your home. If you see them call them out


  8. #8
    sam sanders's Avatar
    sam sanders Guest

    Default Re: Gas line under slab

    Thanks Guys,
    I live in Tucson and most of the time I see this situation is because someone poured an exterior slab over a section of gas line near where is pops out of the ground and comes into the house. For example, the most recent one I saw was running under a back patio slab for less than two feet before it popped up and entered the house. So, you can see why it might seem strange to a client if I make a big deal out of this type of situation (which is pretty common out here). Everything is built on slab out here, so there are no "leaks into basement from the exterior" issues, but I do see the point that if the gas line is adjacent the foundation, and covered by an exterior slab, a leak could work its way up under the house slab and then into the residence. So, that is an explanation I feel comfortable using when asked, "What's the big deal?"
    Sam


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