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

[DangerZoneNick]

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?


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

Thanks!

 

[petersonra]

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.

 

[Jim1959]

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!

 

[paul_arc]

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.

 

[rbalex]

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) ]

 

[DangerZoneNick]

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. :thumbsup:

 

[rbalex]

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.

 

[MAC702]

...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?

 

[petersonra]

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.

 

[rbalex]

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.

 

[GoldDigger]

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.

I would think that a critical part of that 496 system,*which might be hard to achieve in the area of the cab, is a source of clean air.
If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.

 

[DangerZoneNick]

A/C is usually a recirculating system that doesn't "pressurize" the conditioned space. Could you clarify this?

Yes, so it is a "somewhat pressurized" cabin, in that it's only 2/10'' water column pressure, which comes from the air intake system of the AC (so it's not just recirculating inside air). (There is a higher pressure inside the cabin than there is outside of it.)

Basically, threaded conduit connections permit the transmission of gasses through the bulkhead.

That kinda puts us back at square 1 then with the unclassified grommet & caulking then?

I do remember reading that in the 2017 NEC 501.15(A)(1) - Class I Div. I
- Revision to no longer allow conduit bodies (only cabbed elbows) between seal fitting and explosionproof enclosure.
- Increased volume in raceway system created by use of conduit bodies was hazard cited.

If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.

The air intake is on the back side of the cabin, and the edge of the C1D2 zone only extends into the front face of the cabin (right where we're trying to mount this intercom unit).

 

[rbalex]

I would think that a critical part of that 496 system,*which might be hard to achieve in the area of the cab, is a source of clean air.
If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.

A clean air source is usually only a matter of ducting.

 

[petersonra]

I would think that a critical part of that 496 system,*which might be hard to achieve in the area of the cab, is a source of clean air.
If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.

I think usually they just move the intake high enough that it is above the classified area. it is not like the classified area extends indefinitely above ground level.

 

[rbalex]

...

That kinda puts us back at square 1 then with the unclassified grommet & caulking then?

...

This may blow your mind but, if you had adequate pressurization, you could make the opening large enough that vibrations wouldn't cause contact with the conduit and nothing is needed to fill the void.

...

I do remember reading that in the 2017 NEC 501.15(A)(1) - Class I Div. I
- Revision to no longer allow conduit bodies (only cabbed elbows) between seal fitting and explosionproof enclosure.
- Increased volume in raceway system created by use of conduit bodies was hazard cited.

...

That applies only to the enclosure seal - not the boundary seal. No threads have been allowed between the seal and the boundary longer than I've been in the business (nearly 50 years).

 

[AKElectrician]

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?

View attachment 18685View attachment 18686View attachment 18687View attachment 18688
Also sorry my pictures aren't the greatest, and I can't figure out how to rotate them vertically)

Thanks!

https://www.roxtec.com/us/products/solutions/roxtec-spm-seal/ :happyyes:

 

[csc_wyo]

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.

Agreed. I have multiple installations that consist of closed-loop HVAC units in conjunction with a Type Z fresh air purging system.