Classified/Non classified Areas

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I work for a natural gas utility and we have designed a building that has 3 seperate "rooms". One of the rooms is classified as a Class1Div2 and the other two are unclassified. The wall between the classified and unclassified rooms are constructed of 2 layers of 6mil vapor barrier,1/2"FPR over 2 layers Fire rated, staggered, 5/8" drywall with fiber mesh tape and non sanded mud.
Conduit containg 24volt dc circuits will be piercing the wall between the classified and unclassified area. I realize seals are required, but I am unable to find any articles relating to what is required when piercing the wall. Are seals all that is required? My concern is that natural gas could communicate from the classified to the unclassified area through the pierced area around the conduit.

Thank You


Senior Member
Northern illinois
The seals are to contain any potential flame inside the conduit from spreading through the conduit, and to prevent the spread of potentially hazardous gases through the conduit system.

Whether you need to take special precautions to seal around the wall penetrations is probably not part of the scope of the NEC. I am not sure why they put in the vapor barrier. If they are trying to reduce the spread of water or other vapors, you would be defeating the purpose by not resealing the vapor barrier at the point(s) of penetration.

I think you need to maintain the integrity of the vapor barrier, regardless of why they put it there, even if it is not a NEC issue.


Staff member
Mission Viejo, CA
Professional Electrical Engineer
Basically, the electrical installation is not permitted to reduce the integrity of the wall's fire rating. See Section 300.21.

I am curious how you arrived at only Divison 2 for an enclosed room.
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