Aircraft Hangars - Class 1 Div 2 Bottom

[MW Construction]

In a previous post it was said that "For the purposes of Article 513, the bottom is somewhere in Sichuan Provence, China." Why wouldn't the recent clarification of section 511.4(A)(1) (Commercial Garages) that specifically states the finish floor is the horizontal boundry and the soil under the finished floor is not a classified (hazardous) location, also apply to section 513 (Aircraft Hangars)?

Thanks

 

[Rockyd]

501.15(A)(4)ex #2

514.8 Ex #2 May be what your looking for.

513.8 May prove interesting.

500.4

There will be some experts show up...be interesting to see what they have to say.

 

[sgunsel]

See NFPA 409 for aircraft hangers, that is the source for Article 513. I believe it only refers to the "interiors" of pits or other depressions as classified areas since vapors can collect. There is no mention of any other area below floor level. As an example, look at 514 where it specifically addresses underground wiring. Fueling operations add a much greater risk of leakage and/or spillage. If there is indoor fueling in tha hanfger, then 514 would apply and there could be underground classified areas.

 

[rbalex]

In a previous post it was said that "For the purposes of Article 513, the bottom is somewhere in Sichuan Provence, China." Why wouldn't the recent clarification of section 511.4(A)(1) (Commercial Garages) that specifically states the finish floor is the horizontal boundry and the soil under the finished floor is not a classified (hazardous) location, also apply to section 513 (Aircraft Hangars)?

Thanks

I’m not sure which 511.4(A)(1) you’re referring, since it doesn’t appear in either of the last two NEC editions. But even if it did, it still couldn’t be applied to Article 513 in absence of a definite cross-reference to it from Article 514.

This isn’t to say I disagree with your thinking; I never thought the underground should be classified under these conditions. In fact, I’m loath to classify the underground under any conditions. Nevertheless, it is currently a requirement of Section 513.8.

I suspect the current state is a result of unintended consequences. At first the 513.8 content was extracted from NFPA 409. Later NFPA 409 dropped its own specific requirements and referenced “NFPA 70, Article 513.” It isn’t likely to get changed though until someone with a dog in the fight makes a Proposal to do so.

 

[weressl]

I?m not sure which 511.4(A)(1) you?re referring, since it doesn?t appear in either of the last two NEC editions. But even if it did, it still couldn?t be applied to Article 513 in absence of a definite cross-reference to it from Article 514.

This isn?t to say I disagree with your thinking; I never thought the underground should be classified under these conditions. In fact, I?m loath to classify the underground under any conditions. Nevertheless, it is currently a requirement of Section 513.8.

I suspect the current state is a result of unintended consequences. At first the 513.8 content was extracted from NFPA 409. Later NFPA 409 dropped its own specific requirements and referenced ?NFPA 70, Article 513.? It isn?t likely to get changed though until someone with a dog in the fight makes a Proposal to do so.

Isn't the issue that any below grade level indentations that may contain electrical equipment should be Division 1? Ex. a floor-box.

 

[rbalex]

Isn't the issue that any below grade level indentations that may contain electrical equipment should be Division 1? Ex. a floor-box.

Underground and below grade aren't quite the same thing since something underground is not generally exposed to direct and immediate contamination.

In the most general since you're still correct - a footstep that leaves a footprint beneath a Division 2 location could be Division 1 in the "classic" sense. However, both of the most most common general domestic electrical area classification documents (NFPA 497 and API RP500) recognize throughout their diagrams the underground itself is not classified.

In fact, in a few select cases, below grade isn't classified either. For example, see API RP500 Figure 6 or the third line in Figure 27. These recognize that other factors, such as a large horizontal/verticle ratio of the depression or a very low potential rate of release are also reasonable considerations when determining the "collection" of below grade ignitable materials. And of course, lighter than air materials will tend to collect in high points rather than depressions.