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Thread: Area Classification Above A Trench

  1. #11
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    Quote Originally Posted by rbalex View Post
    18" is pretty much a historic minimum. "Judgment" could put it as much as 10' although it isn't likely.
    OK, I agree. I really would like to see NFPA 497 address this though.

  2. #12
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    Quote Originally Posted by circuitrider View Post
    OK, I agree. I really would like to see NFPA 497 address this though.
    NFPA 497 goes through a revision cycle just as the NEC does. Make a Public Input.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #13
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    Quote Originally Posted by rbalex View Post
    A closed piping system in a trench (or anywhere else) does not require classification.
    Not sure if you consider 'closed piping system' but some AGA standards and gas utility meter/reg station standards define 15' from flanged connections as Cl I Div 2. Although this doesn't sound like what the OP has.

  4. #14
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    Quote Originally Posted by nhee2 View Post
    Not sure if you consider 'closed piping system' but some AGA standards and gas utility meter/reg station standards define 15' from flanged connections as Cl I Div 2. Although this doesn't sound like what the OP has.
    This isn’t the OP’s case. In the scenario discussed in the OP, the pressure differential between the Division 1 and unclassified locations is essentially zero and 18” is the common hazard radius.

    Closed piping has no designed route to atmosphere, such as a relief valve. Other (non-catastrophic) potential routes may be evaluated based on pressure differential, flange pressure rating, anticipated flow rates, etc. Typically, a 300psi rated flange on a 100 psi rated piping system would still be considered “closed”.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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