Naptha and API RP 500

[Isaiah]

Client wants to extended the area class 25’ (at 2 feet above grade) due to process that contains Naptha, of only 1%.
this seems like overkill to me and may affect equipment within the new boundary, rated only Nema 4X.
Is there anything in API RP500 that defines min percentiles of “heavier than air vapors”
required to create the above condition?

 

[rbalex]

Indirectly; see Annex B for ventilation/fugitive emissions calculations. A more direct approach would be a review of NFPA 497, Table 4.4.2.which says the LEL for naphtha is about 1.1%.

Personally, I'd go along with your client and extend the envelope. Type 4X enclosures usually do fine in Division 2. The question would be the contents of the enclosures and potential boundary sealing issues.

 

[Isaiah]

Indirectly; see Annex B for ventilation/fugitive emissions calculations. A more direct approach would be a review of NFPA 497, Table 4.4.2.which says the LEL for naphtha is about 1.1%.

Personally, I'd go along with your client and extend the envelope. Type 4X enclosures usually do fine in Division 2. The question would be the contents of the enclosures and potential boundary sealing issues.
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thanks Bob great info as usual