100# Propane bottle Area Classification

[ceubanks9]

I'm installing a generator skid that is run off of 6-100# propane bottles. The contractor is questioning me about area classification for the propane bottles. Everything i have read does not get into detail for that small of a system or for that low of pressure. (regulated pressure is set at 25psi)

Does anybody have any experience with this? Can someone share a NEC reference or NFPA article that would prove there is or is not a class 1 div 2 radius around the propane bottles.

 

[rbalex]

Sealed storage tanks are covered by NFPA 30, Flammable and Combustible Liquids Code. See NFPA 30, Table 7.3.3 for general guidance. For outdoor storage with properly rated connectors, as long as there are no intentional releases to atmosphere and no pressure relief devices on the tanks, the general location is unclassified. (It's just a larger version of an outdoor propane grill).

 

[petersonra]

Don't all those kinds of Tanks come with a pressure relief device now?

 

[rbalex]

Don't all those kinds of Tanks come with a pressure relief device now?

Have you seen one?

 

[petersonra]

Have you seen one?

I looked it up. What I found suggested that only propane cylinders under 40 pounds have them.

 

[rbalex]

I looked it up. What I found suggested that only propane cylinders under 40 pounds have them.

Just to satisfy my curiosity, what standard did you find it in? It does make sense; the lower pressure rated tanks could definitely be affected by ambient temperature. I'm was just unaware of it being a general requirement.

 

[petersonra]

NFPA 58

 

[rbalex]

NFPA 58

I had to reeducate myself a bit. My original evaluation was still ok but the presence/absence of a relief valve has changed a bit. Thanks for the reference.

NFPA 58, Sections 5.9.2 and 6.25 with their associated Tables and surrounding explanatory text cover the issue pretty well. For static tanks, such as mentioned in the OP, the primary concern is filling. Typically in those cases, regulators and relief systems are associated with the delivery system. Once set in place, and connected properly to the utilization system there is little concern of "fugitive emissions." Some tanks with low pressure ratings may be more subject to ambient temperatures and some form of pressure relief is warranted.

My general, personal experience with vessel pressure relief is with high pressure continuous processes where over-pressure may be a condition of various process upsets.

NFPA 58, Section 6.26 recognizes small "static" residential and commercial systems rarely require auxiliary pressure relief.

It is important to note a relief system will automatically create a Division 1 location under NEC Section 500.5(B)(1) in the immediate vicinity of its exhaust port with a corresponding Division 2 location surrounding it. [Section 500.5(B)(2)] The dimensions of the envelope are determined by the pressures and anticipated release rates. Catastrophic releases are not covered, emergency response is required.