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Thread: Difference between ClassI Div.1 and Div.2

  1. #1
    Join Date
    Jun 2006

    Question Difference between ClassI Div.1 and Div.2

    Iím having to do a cost comparison for a hazardous location, Group B specifically hydrogen. My company is planning on installing a ClassI Div1 area for their use with the gas. I have studied the code and know the requirements for Div1 and Div2, and have come to the conclusion that a Div2 location would work just as well.

    I was wondering if there was anyway to find out how much more it would be to place various equipment in one division vs. another. To illustrate how much more it cost to install a Div1 than to install a Div2. If anyone can help I would appreciate it.


  2. #2
    Join Date
    Apr 2004
    Mission Viejo, CA
    You begin with the fact that equipment that is arcing, sparking or heat producing (ASH) will generally need to be in sealed, explosion-proof enclosures in either Division; so essentially that is a fixed cost.

    After that, things get messy - especially for Group B. It is very difficult to summarize here but, excluding intrinsically safe systems, for most installations everything including conduit fittings will need to be or in explosion-proof enclosures in Division 1 and not everything needs to be in Division 2.

    Motors will be a particular problem since very few are listed for Division 1, Group B use although Division 2 applications are fairly easy to achieve.

    Typically the cost of a Division 1 installation will be 35 to 75% higher than one for Division 2 with similar operating functions but it is impossible to be more specific without knowing the actual scope of the project.

    I would look very carefully at the classified envelope. Review both NFPA 497 and API RP 500. You will probably find the locations that actually need to be classified Division 1 are few and relatively small.

    It is rather typical to grossly over-classify ("just to be safe") and then when the price tag begins to show to attempt to avoid the consequences by “cheating” in the Division 1 location. This often leads to an installation that wouldn't be safe in Division 2 either.
    Last edited by rbalex; 06-09-06 at 12:49 PM.
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
    Join Date
    Jun 2006
    Ok thanks for the information that was useful in my problem.

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