500.7(K) interpretation

[Isaiah]

In this waste-water treatment plant, there's a very long corridor running below aeration ponds which appears to be about 300 feet in length by 10 feet high and 15 feet wide. It seems to be well ventilated. A 4" Natural Gas line runs the entire length of the corridor and several combustible gas detectors are strewn along the way. None of the equipment is rated for CID2, i.e. no conduit seals, Nema 7 enclosures etc. (Plant was built in the 50's - cant even find area classification dwgs)
I believe NEC 500.7(K) applies and the corridor can be declassified - any comments?

 

[don_resqcapt19]

That section very very difficult to comply with.

 

[nhee2]

Are there vents/bleeds/leakage points in the NG pipe? A pipe by itself does not necessarily create a haz area, even if indoors - for instance if its a long run of welded pipe.

 

[Isaiah]

Are there vents/bleeds/leakage points in the NG pipe? A pipe by itself does not necessarily create a haz area, even if indoors - for instance if its a long run of welded pipe.

Yes has flanges and valves


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[Isaiah]

That section very very difficult to comply with.

Do you think the installation should be fit for Division 2?


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[rbalex]

Do you think the installation should be fit for Division 2?


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Don already mentioned Section 500.7(K) was difficult to comply with, This is because the NEC only recognizes three applications for gas detectors in Classified locations. They are listed in Subsections 500.7(K) (1), (2), and (3). The description of your installation doesn't match any of them.

nhee2 asked about, "vents/bleeds/leakage points". This question rooted in Section 500.5(B)(2) IN No.2. Your response was there were valves and flanges. We could stop there and say it answers your question. However, as installed, do those valves and flanges create "vents/bleeds/leakage points"?

 

[Isaiah]

Thanks Bob. I went out and double-checked the entire run of pipe and was surprised - I could not find any vents, bleeds or leak points.

 

[rbalex]

Thanks Bob. I went out and double-checked the entire run of pipe and was surprised - I could not find any vents, bleeds or leak points.

So how would you classify the location?

 

[Isaiah]

Without a viable source of vapor I would say the area should remain unclassified. There seems to be adequate ventilation throughout the corridor even though technically it is not an 'open' area.

 

[petersonra]

Without a viable source of vapor I would say the area should remain unclassified. There seems to be adequate ventilation throughout the corridor even though technically it is not an 'open' area.

Why would ventilation be an issue if there is no source of flammable gas?

 

[Bwas]

Aeration tanks will likely have some classified locations associated with them per NFPA 820. Those gasses and the classified envelopes can extend outside the tank and down to areas below. You need to confirm if that affects this situation too.

 

[Isaiah]

Aeration tanks will likely have some classified locations associated with them per NFPA 820. Those gasses and the classified envelopes can extend outside the tank and down to areas below. You need to confirm if that affects this situation too.

You’re right. Problem is, this client seems to have no area class documentation whatsoever which to me, is unbelievable.


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[rbalex]

le" le

You’re right. Problem is, this client seems to have no area class documentation whatsoever which to me, is unbelievable.

I've said before that electrical area classification is not trivial; thankfully, it isn't rocket science either.

The original issue was simply the use of gas detectors in the presence of a natural gas line. We have already dealt with those.

The issues of NFPA 820 and lack of proper documentation have been subsequently added. I'll deal with them in reverse order. "Proper documentation" wasn't formally required until the 1999 NEC. [then Section 500-3(b)]. Bwas's reference to NFPA 820 is well taken; however, it was developed in the early 1980s. So neither factor was applicable to the original installation. (1950s per the OP)

It is my opinion that gas detectors imply at least a Class I, Division 2 location. Otherwise, why have them? If you do have them, what will you do if they detect gas? The NEC doesn't address that directly although some of the Standards referenced in Section 500.7(K) INs do. Only those Standards that have ANSI sanctions are enforceable by Fed or State OSHAs.

My recommendation is to suggest to your client that the location(s) be formally documented, If you choose to leave the location(s) unclassified - document that reasoning as well.

 

[Isaiah]

le" leI've said before that electrical area classification is not trivial; thankfully, it isn't rocket science either.

The original issue was simply the use of gas detectors in the presence of a natural gas line. We have already dealt with those.

The issues of NFPA 820 and lack of proper documentation have been subsequently added. I'll deal with them in reverse order. "Proper documentation" wasn't formally required until the 1999 NEC. [then Section 500-3(b)]. Bwas's reference to NFPA 820 is well taken; however, it was developed in the early 1980s. So neither factor was applicable to the original installation. (1950s per the OP)

It is my opinion that gas detectors imply at least a Class I, Division 2 location. Otherwise, why have them? If you do have them, what will you do if they detect gas? The NEC doesn't address that directly although some of the Standards referenced in Section 500.7(K) INs do. Only those Standards that have ANSI sanctions are enforceable by Fed or State OSHAs.

My recommendation is to suggest to your client that the location(s) be formally documented, If you choose to leave the location(s) unclassified - document that reasoning as well.

Right Bob. My first reaction when I saw the detectors was, “CID2 location”. But, I couldn’t make a case for it since there were no true sources of vapor contribution. These are ‘waste water people‘ who don’t seem to take very seriously articles 500/501.
As Bwas stated there are probably legitimate sources above grade they aren’t even aware of. The plant is located in a very high seismic area which, in my opinion makes an argument for Division 2 re-classification. More to come...
Thanks to all


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