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Thread: Moving a C1D2 zone / unclassified zone boundary

  1. #1
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    Moving a C1D2 zone / unclassified zone boundary

    This question pertains to a typical open factory floor, enclosed environment scenario.

    By definition the C1D2 zone boundary extends 25 ft radially out horizontally from the source producing hazardous vapor fumes (at the center of the C1D1 zone), and up to 3' above the grade. Viewed from above this is circle with 25' diameter, with the unclassified zone anywhere beyond the D2 zone boundary.

    Is it acceptable to effectively move the D2 zone boundary inwards some amount by installing a vertical continuous subwall extending up from the floor a minimum of 3' high such that any potentially hazardous vapors that can collect near the floor would be blocked from further outward travel ? (thus effectively contained) This is an idea similar to what is common practice for large outdoor petroleum storage tanks which all have a containment control berm around the tank to catch any liquid leakage or rupture from escaping further away.

    We are seeking to install a piece of large industrial equipment on a factory floor in a location now determined to fall about 7' inside the D2 zone outer boundary. This equipment is not designed for operation in a D2 zone, and modifications to become compliant to do so may be complicated and very expensive. For us a much simpler solution may be facilities-related (making the D2 zone smaller) rather than machine-design-related.

    Are there any P.E.s that could provide an opinion here ? thanks

  2. #2
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    It sounds like an interesting concept.

    Is it possible to put some piece of the machine that is suitable for the area in that small chunk of area? It is usually not that hard or expensive to make something suitable for C1D2.

    It is also possible that the C1D1 area was not properly classified to begin with.

    Perhaps it is time to pay someone with expertise in this area to take a look.

    Not a P.E.
    Bob

  3. #3
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    Quote Originally Posted by petersonra View Post
    It sounds like an interesting concept.

    Is it possible to put some piece of the machine that is suitable for the area in that small chunk of area? It is usually not that hard or expensive to make something suitable for C1D2.

    It is also possible that the C1D1 area was not properly classified to begin with.

    Perhaps it is time to pay someone with expertise in this area to take a look.

    Not a P.E.
    Our machine uses very high voltage (> 100K VDC) in normal operation so the changes to power wiring and control wiring throughout and to the basic architecture of the machine are so extensive that they really aren't a viable option at this point.

    The source of the C1D1 flammable vapor fumes is a printing press that uses solvent-laden inks, so this C1D1 determination is correctly determined by the press manufacturer.

  4. #4
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    I would normally defer to our colleague sgunsel on this as far as area classification for printing processes is concerned, but I would like to know the standard used to classify the location anyway. From part of your second response ("... solvent-laden inks ...") I suspect the primary reference standard is NFPA 33. It doesn't directly address your proposed solution. Fortunately, NFPA 497 the "general" area classification standard does:
    Section 5.2.2.4 In cases in which an unpierced barrier, such as a blank wall, completely prevents the spread of the combustible material, the area classification does not extend beyond the barrier.
    One thing that must also be considered is that the gases/vapors could "extend beyond the barrier" where it doesn't completely cut off the "normal" classification envelope, typically with a new hazard radius from the cutoff point. The new radius is the differential between original radius and the cutoff point.
    Last edited by rbalex; 11-02-13 at 02:10 PM.
    "Bob"
    Robert B. Alexander, P.E.
    "I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)

  5. #5
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    Quote Originally Posted by brtsvg View Post
    Our machine uses very high voltage (> 100K VDC) in normal operation so the changes to power wiring and control wiring throughout and to the basic architecture of the machine are so extensive that they really aren't a viable option at this point.
    the point is that there might be some part of the machine suitable to put in the classified area. you are only talking about a small area that is classified that is at issue.
    Bob

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