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Thread: use NFPA and NEC to reduce bldg from CID1 to CID2?

  1. #1
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    use NFPA and NEC to reduce bldg from CID1 to CID2?

    I want to change a building Area Classification from Class I, Division 1 to Class I Division 2 using Fans/Gas Detectors in accordance with NFPA 497 and NEC 500.7(K)(1).
    Is this a viable solution?

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    Quote Originally Posted by Dale001289 View Post
    I want to change a building Area Classification from Class I, Division 1 to Class I Division 2 using Fans/Gas Detectors in accordance with NFPA 497 and NEC 500.7(K)(1).
    Is this a viable solution?
    I have always thought the gas detection options were pretty limited in their utility. I think you probably will need to pay someone competant to make this call for you and come up with a design.
    Bob

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    Quote Originally Posted by Dale001289 View Post
    I want to change a building Area Classification from Class I, Division 1 to Class I Division 2 using Fans/Gas Detectors in accordance with NFPA 497 and NEC 500.7(K)(1).
    Is this a viable solution?
    You need to answer two questions first:

    1. Why is the location classified as Division 1 in the first place?
    2. Which of the three Subsections of Section 500.7(K) are you applying - (1), (2), or (3)?
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    From my understanding and a logic standpoint, it is always better to reduce the presence of explosive gasses to reduce the chance of ignition. So the short answer would be yes. However, designing the method and determining the classification is obviously better left to those educated and qualified to do this.


    I know what I don't know, and I know where to go to find it!

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    Quote Originally Posted by rbalex View Post
    You need to answer two questions first:

    1. Why is the location classified as Division 1 in the first place?
    2. Which of the three Subsections of Section 500.7(K) are you applying - (1), (2), or (3)?
    It’s an atypical scenario. The building has been designated simply as “Hazardous Materials Building” but no one is sure what exactly the materials will be housed within – one must assume both lighter than air as well as heavier than air hazardous vapors could be installed.

    Using 500.7(K)(1)


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    Quote Originally Posted by Dale001289 View Post
    It’s an atypical scenario. The building has been designated simply as “Hazardous Materials Building” but no one is sure what exactly the materials will be housed within – one must assume both lighter than air as well as heavier than air hazardous vapors could be installed.

    Using 500.7(K)(1)
    1. This is not “atypical”. This is a WAG.
    2. If you were planning on ventilating it properly, why are you using 500.7(K)(1)?

    Personally, I wouldn’t touch it.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    Quote Originally Posted by rbalex View Post
    1. This is not “atypical”. This is a WAG.
    2. If you were planning on ventilating it properly, why are you using 500.7(K)(1)?

    Personally, I wouldn’t touch it.
    This client doesn't trust exhaust fan ventilation alone. He wants more assurance - a gas detection system along with alarms/shutdown of power to the building (its actually a single room) will provide that.
    I don't see why everyone on this string is so apprehensive about doing this - its perfectly legal according to NFPA 497 and NEC.

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    Quote Originally Posted by Dale001289 View Post
    The building has been designated simply as “Hazardous Materials Building” but no one is sure what exactly the materials will be housed within – one must assume both lighter than air as well as heavier than air hazardous vapors could be installed.
    I don't see how you can assume anything and still get it right. I doubt anyone competent to do so would want to put his name or his PE seal on something with so little information.

    I suppose you could classify the whole thing as Class I, Division 1, Groups A, B, C and D. Might find that a bit hard to make work though.

    However, reading what 500.7(K)(1) says

    (1) Inadequate Ventilation. In a Class I, Division 1 location
    that is so classified due to inadequate ventilation, electrical
    equipment suitable for Class I, Division 2 locations shall be
    permitted. Combustible gas detection equipment shall be listed
    for Class I, Division 1, for the appropriate material group, and
    for the detection of the specific gas or vapor to be encountered.
    It appears you can already use C1D2 stuff (other than the gas detection equipment) so what do you gain by reclassifying it?
    Bob

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    Quote Originally Posted by petersonra View Post
    I don't see how you can assume anything and still get it right. I doubt anyone competent to do so would want to put his name or his PE seal on something with so little information.

    I suppose you could classify the whole thing as Class I, Division 1, Groups A, B, C and D. Might find that a bit hard to make work though.

    However, reading what 500.7(K)(1) says



    It appears you can already use C1D2 stuff (other than the gas detection equipment) so what do you gain by reclassifying it?
    Well, reasonable assumptions are made all the time in this business. If one insisted solely on absolutes, nothing would get done on time and costs would go through the roof. Just like your comment "classify the whole thing as Class I, Division 1, Groups A, B, C and D". This philosophy will certainly work - but isn't very cost effective I'm afraid.

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    Quote Originally Posted by Dale001289 View Post
    ... - its perfectly legal according to NFPA 497 and NEC.
    No, actually it isn't.

    Read all of Section 500.7 carefully, then Section 500.7(K) even more carefully, then Subsection 500.7(K)(1) MUCH more carefully.

    A Combustible Gas Detection System (CGDS) is a protection technique, not a basis for classifying a location. Subsection 500.7(K)(1) permits using Class I, Division 2 equipment/wiring methods but not "de-classifying" the location. The location is still Class I, Division 1.

    From Section 500.8(K) main text:
    The type of detection equipment, its listing, installation
    location(s), alarm and shutdown criteria, and calibration
    frequency shall be documented when combustible gas detectors
    are used as a protection technique.
    Do you plan to provide CGDS for every potential gas? It the client really prepared for all the documentation/maintenance a CGDS requires (for every potential gas)? See the first three Informational Notes. While they are not "Code", since the referenced documents are ANSI sanctioned, they are OSHA enforceable.

    Proper ventilation is a recognized basis for classifying a location and is far more reliable and easier to maintain than a CGDS. EDIT ADD (after seeing your last response) It's more cost effective too.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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