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Thread: Sealing Around Hole Going from Class 1 Div 2 into Unclassified, Pressurized Cabin

  1. #1
    Join Date
    Oct 2017
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    Garland, TX, US
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    Sealing Around Hole Going from Class 1 Div 2 into Unclassified, Pressurized Cabin

    Good afternoon guys,

    I have this intercom unit that has 2 lines coming out the bottom (or possibly just one if we can fit the audio and power cables through the one hole) that is positioned in a Class 1 Division 2 hazardous zone on the outside of the cabin of a drilling rig.

    We have ordered some conduit sealing fittings, but the problem arises with the actual process of passing the conduit line through the wall. It's a 3/4''NPT threaded pipe, so we will have to cut a hole in the wall large enough to pass the conduit through, but in order to prevent the gasses from also entering through the wall, we're not sure exactly what to use. My initial thought was to just use a rubber grommet, but others are saying that we also need additional caulking around the ingress hole. However, I can't seem to find any sort of caulking or sealant that's rated for Class 1 Div 2 (besides the stuff that goes inside of the conduit sealing itself).

    What are your thoughts?

    Click image for larger version. 

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    Also sorry my pictures aren't the greatest, and I can't figure out how to rotate them vertically)

    Thanks!

  2. #2
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    If it is pressurized how would any hazardous gases pass into the cabin?

    My personal inclination would be to talk to the people that made the cabin and ask them to sell you whatever material they use to repair openings they make in the walls of the cabin.
    Bob

  3. #3
    Join Date
    Sep 2016
    Location
    Longmont, CO
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    I don't think the product you use has to be rated CID2, I would just use a good quality caulking and be done with it. That's a nice looking rig!

  4. #4
    Join Date
    Oct 2017
    Location
    CA
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    11
    Are you sure of the area classification? The speaker and enclosure in the picture are rated class 1 div 1. Either way, you need a bulkhead fitting through the wall. Myers makes one that's a hub type, or you can get a conduit pass through from crouse hinds.

    Don't forget the seal-off changing area classifications.

  5. #5
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
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    To summarize the situation:

    • The unclassified room is pressurized.
    • The immediate outside is Class I, Division 2.
    • The installation is on a drilling rig.

    Some assumptions/observations:

    • I expect the overall environment has substantial vibrations. I couldn’t tell if it was offshore or not; it wouldn’t matter too much either way.
    • I assume the pressurization system has a proper air source.

    Some comments:

    • The immediate electrical area classification under concern appears to be correct and an explosionproof horn and controller are still appropriate for Division 2.
    • Were it not for vibrations potentially damaging the conduit at the penetration and assuming an adequate pressurizing system, nothing would be needed to "seal" around the conduit. Some mechanical protection is appropriate.
    • A boundary seal for the conduit is unnecessary. See Section 501.15(B)(2) Exception No. 3​ and its reference to NFPA 496.
    • The horn/controller assembly does need to be sealed. Unless the horn/controller are listed as an assembly together (this is likely, but not certain) there appears to be a seal missing between them. The rules for enclosure seals are basically the same for Division 1 and 2. [See Sections 501.15(A)(1)(3) and 501.15 (B)(1) ]
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #6
    Join Date
    Oct 2017
    Location
    Garland, TX, US
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    3
    Thanks for all of the replies, you guys have been very informative.
    It is a land rig, and the div 2 zone extends right up against that wall of the cabin.

    The cabin itself is "pressurized" due to having A/C inside, but we are in the process of talking with our vendor about redesigning other aspects of the cabin as well, so I can ask about adding holes and what material they use to repair openings. In the case that the A/C is turned off, we don't want there to be any way for hazardous gasses to enter the cabin.

    I'm thinking that the Myers Through-Bulkhead Connector, Aluminum, Rigid/IMC Conduit, 3/4'' was what I was looking for. I know I had come across this in my previous research but I couldn't find it on any of the NEC diagrams so I didn't think it would be necessary. But as rbalex was saying, we will likely be encountering a lot of vibration during drilling, and I like how these connectors screw together through the wall.

  7. #7
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    This blows my assumptions. Unless the installation is consistent with NFPA 496, it's hard to say it's "pressurized".

    A bulkhead connector violates Section 501.15(B)(2): "... The conduit run between the conduit seal and the point at which the conduit leaves the Division 2 location shall contain no union, coupling, box, or other fitting except for a listed explosionproof reducer installed at the conduit seal." Basically, threaded conduit connections permit the transmission of gasses through the bulkhead.

    Depending on the location, the horn/controller enclosure seal may do "double-duty" as the boundary seal also but the violation noted above would still be in effect.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  8. #8
    Join Date
    Jul 2007
    Location
    Clark County, NV
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    Quote Originally Posted by DangerZoneNick View Post
    ...The cabin itself is "pressurized" due to having A/C inside, but we are in the process of talking with our vendor about redesigning other aspects of the cabin as well, so I can ask about adding holes and what material they use to repair openings. In the case that the A/C is turned off, we don't want there to be any way for hazardous gasses to enter the cabin. ...
    A/C is usually a recirculating system that doesn't "pressurize" the conditioned space. Could you clarify this?

  9. #9
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    What I have seen of such rooms is while they are a conditioned space they also are pressurized. It is not just an A/C unit. I never looked real close at how it is done but opening the door I could feel air coming out and more often as not there is an air lock to reduce the conditioned air loss. In fact, I can't recall any that did not have an air lock of some sort. Nothing real elaborate. IIRC, most times it was a hallway like structure with a door at each end to get into the control room.

    I do recall one that had a picnic table outside the control room with a yellow line painted around it. This was the designated smoking area for the building and somehow they had determined that the area inside the yellow box painted on the floor was not classified, but the space surrounding the picnic table was Class I, div 2. I always thought that was a curious thing.
    Bob

  10. #10
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    HVAC can be an integral part of an NFPA 496 system. A Type Z system isn’t very difficult to achieve with HVAC. It still needs to be an NFPA 496 system though.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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