Seals Between Two Different Cl I Div 2 Locations

[MDS@CGT]

Ok here are the details.

Two seperate Cl I Div 2 locations.
Both locations outdoors.
Both locations same lighter than air gas.

Here is the question:

I have always been told that for our purposes (outdoors, lighter than air gas ) that the ground was neutral for classification purposes. That is, it can be considered the boundary. So, for a conduit entering the ground in a Div 2 location and leaving the ground in an unclassified location, the seal could be in either the classified or unclassified location. Preferrably in the classified location to limit exposure.
But, what about a conduit that enters the ground in one Cl I Div 2 location and exits the ground in another Cl I Div 2 location? If the ground is neutral, I don't need a seal at all. If it is unclassified, I need two seals.

What do you all say?

Now, if you agree that I don't need a seal at all, how do I prove that the ground is neutral for classification purposes ? I would like to see it in black and white somewhere.

 

[petersonra]

I don't know what "neutral" means. AFAIK, it is either classified or it is not. I'd be inclined to say the conduit started in a C1D2 area, went through an unclassified area and entered another C1D2 area.

 

[rbalex]

There is no recognized Standard that ever hinted that the underground is ?neutral.? Some older Standards were not entirely consistent since a rational argument can be made that underground is either unclassified or, in some cases, Division 1 (but not Division 2) for heavier than air ignitable materials. The underground was always unclassified for locations classified for lighter than air materials. The current Standards are now more or less consistent that underground is considered unclassified in any case.

There are two boundaries described in the OP and a ?boundary seal? must exist within 10? of each stubup. It can?t be in the underground part of the run because it must be accessible. Depending on the terminus of the run within each Division 2 location a single seal may serve ?double duty? by acting as both the boundary seal and possibly an enclosure seal.

 

[MDS@CGT]

Robert,

Thanks for your reply. One more point if you don't mind. The conduit entering the ground in one Cl I Div 2 area and exiting the ground in another Cl I Div 2 area does not go anywhere else. Since there is no equipment underground, what would be the point in requiring a seal in this instance ? That is, other than complying with the letter of the NEC. Obviously, the boundary seal between a Cl I Div 2 and an unclassified area is to prevent gas from migrating to an area where an ignition source might exist due to general purpose equipment. That would not be the case in this instance since the conduit terminates in another Cl I Div 2 area. I appreciate your comments.

 

[rbalex]

Truthfully, this is an issue where my former colleagues on CMP14 and I disagree.

First though, ??complying with the letter of the NEC? is the fundamental reason. Second is a bit more subtle. My opinion is that seals between Division 1 and other locations are to prevent the migration of gases and flames since the presence of gases are a ?normal? condition for Division 1. Seals between Division 2 and Unclassified locations are to prevent the propagation of flames only, since both are ?abnormal? conditions.

CMP14 dug themselves into a hole when they committed to ?non-explosionproof? seals between Division 2 and unclassified locations. My position is that if you believe gases may migrate you must also be concerned that they may be ignited and a ?non-explosionproof? seal is useless.

Getting back to your question, for a ?lighter than air? application, I personally see no benefit for seals at grade if the raceways are sealed at the terminus. However, if the locations are classified for reasons of different primary sources then we don?t want a flame in one location propagated to the other via the underground raceway system.