Area Classification for Sump Outside of a Chemical Refinery 2

[sjmgd977]

All: I have to determine what the correct area classification is for a sump near an oily trench area.

From what I have read so far, NFPA 497 suggests that if you have the presence of liquid hydrocarbon detected, you would have Class 1 Division 1, classification. According to what else I found, Figure 5.9.7 of NFPA 497 seems to support Class 1 Division 1 in the sump and Class 1 Division 2 is used above grade- 18 inches above the sump.

Is this analysis correct?

Also, if I decide to use Intrinsically Safe Barriers for any field devices, can I avoid use of seal-off fittings?

Please advise.

 

[786392]

Dear
Although basically your narration/explaination and derived inference all seem OK!

However it may be more useful/pertinent if any image or pictorial dispay of the situation under discussion is shared with forum colleagues.

This may get you very close to your answer I believe.

Best Regards
Qalander(Chem)

 

[JLSeagull]

There is more to an intrinsically safe installation than the barriers. Examples include special marking, IS signal segregation from non IS signals, etc.

 

[sjmgd977]

Thank you very much for your comments. I will try to post some pics soon.

 

[sjmgd977]

JLSeagull: Thanks for your insight. I am aware of the fact that both the instrument and the barrier have to be IS rated and I am aware that wiring for IS has to be segregated from other forms of wiring.

Does anyone happen to know if you can use Intrinsically safe wiring in LIEU of say explosion proof junction boxes or seal-off fittings inside a Class 1 Division 1 area?

This was what I was hoping to understand.

Also, does anyone have any information from API RP 500(?) that would either enhance or contradict what I said above about the area around the sump and the like? I was of the understanding that API 500 was written for areas of the petrochem facility that were directly involved with processing of hydrocarbon products where NFPA 497 was more for the areas NOT associated with hydrocarbon products (such as the area where I am doing work currently?)

Is my statement correct?

 

[rbalex]

API RP 500 will confirm NFPA 497. Technically, both are Recommended Practices rather than Standards. They self-define their Scopes as "petroleum facilities" and "chemical facilities" respectively; but basically it is BIG vs. small. NFPA 497 generally defers to API RP 500 for large systems. RP 500 defers to NFPA 497 for determining the "Group" and other properties of the materials involved.

Article 504 is the basic IS installation standard. Beyond what JLSeagull mentioned, an IS installation must conform to a manufacturer's "Control Drawing"(504.10(A)). Proper grounding (504.50) and bonding (504.60) are also commonly overlooked and the requirements are not nearly as relaxed as one might expect. Sealing requirements are in Section 504.70.

 

[sjmgd977]

rbalex:

1st, thanks for your reply.

Do you have to have seal-off fittings IN ADDITION to providing the intrinsically safe barriers?

 

[rbalex]

Assuming the installation is consistent with Art 504, typically the only required seals would be boundary seals and they aren't required to be explosionproof.

Occasionally, process instrumentation or other equipment with direct interfaces to the process materials may need seals. See 504.70 Exception.