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Thread: Area Classification Above A Trench

  1. #11
    Join Date
    Feb 2014
    Location
    Upstate SC
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    15
    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
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
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    5,238
    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
    Join Date
    Aug 2011
    Location
    NH
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    248
    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
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
    Posts
    5,238
    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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