Classification of Above Ground LPG Storage Tanks

[ericwg]

First, a brief summary RE: the situation I'll be asking about. I am doing the electrical design for a multi-building site (in CA) for which the design is mostly commercial. One of the buildings has a mixed B/R2 occupancy. Providing fuel for an optional standby engine generator, HVAC, and some appliances is a pair of above ground 1,000 gallon LPG (cylinder) tanks. The piping for each tank goes underground immediately after leaving the tank, one routing to the generator, the other routing to the building. Per Article 6.4 of NFPA 58 I am aware that these tanks require a minimum spacing of 3ft from each other and 25ft minimum distance from buildings, a group of buildings, or the line of adjoining property that can be built upon. What I am having some trouble with is confirming the Class/Division rating and scope of classified area. I will state what I have come up with below. I would really appreciate feedback confirming whether you think I'm correct or not, and if not, providing relevant references backing your claim.

1) Class I / Division 2: The Class I rating is fairly obvious. While I believe this to be a Division 2 area, I have run across a few claims that it is Division 1. Per NFPA 497, the definition of a Class I, Division 2 area states (in short) that the material will be "...normally confined within closed containers from which they can escape only in case of accidental rupture or breakdown of such containers" or in which "...ignitable concentrations of flammable (material) are normally prevented by positive mechanical ventilation and which might become hazardous through failure or abnormal operation of the ventilating equipment". The LPG in these tanks should never make it outside of these tanks except in some kind of abnormal condition, as described previously. Even during filling, the system should be sealed with only a miniscule amount of vapor escaping. Bottom line, my high level understanding of the Division ratings is that Division 1 = normal, Division 2 = abnormal. Thus, I believe the Division 2 rating to be appropriate.

2) Definition of Classified Area Around Tank: When it comes to fuel dispensing, which I am also dealing with at this site, Figures 514.3 and 514.3(B) from NFPA 70 make it crystal clear what the classified area around the dispenser looks like. I am trying to ascertain what the classified area looks like around the LPG tanks. After digging deeper into NFPA 497 (2017), I came across Figure 5.10.4(a) - Product Storage Tank Located Outdoors, at Grade. The material that is being stored is a flammable liquid. I am attaching a snapshot of that figure. Of all the figures in NFPA 497, this one really looks like it best applies to my situation. If I am reading the figure correctly, it basically states that the classified area extending 10ft out from the surface of the tank and in a 10ft radius around the vent would be Division 2, while the area in a 5ft radius around the vent would be Division 1. Since there are no sumps or trenches around my tanks, the classified area would only exist above grade. If true, as long as I keep any electrical wiring at minimum of 10ft from the surface of the tanks or have it below grade, it should not need to adhere to Article 500 requirements.

Correct? Thanks for reading.

-Eric

 

[rbalex]

Consider Article 515.(Bulk Storage) Read the Scope [Section 515.1] to establish applicability. Section 515.3 addresses classifications. Of course, the whole Article applies and there are some above and underground wiring considerations.

 

[ericwg]

Consider Article 515.(Bulk Storage) Read the Scope [Section 515.1] to establish applicability. Section 515.3 addresses classifications. Of course, the whole Article applies and there are some above and underground wiring considerations.

Thank you so much for your response Bob. As far as considering Article 515, I actually did. However, I am hung up on 515.1 which defines the Scope of this section - Bulk Storage Plants. You left off the word "Plants" but I think that is an important descriptor. From 515.1:

This article covers a property or portion of a property where flammable liquids are received by tank vessel, pipelines, tank car, or tank vehicle and are stored or blended in bulk for the purpose of distributing such liquids by tank vessel, pipeline, tank car, tank vehicle, portable tank, or container.

This might seem like semantics, but in the situation I've described, we are not storing LPG for the purposes of distributing it. Yeah, I'm a little hung up on "pipeline", however, we employ PEX to transfer LPG from our tanks to the generator and building for the purposes of consumption/use. I assume the definition of pipeline must include pipe. Is PEX really a pipe? When you dig deeper into Article 515 it seems apparent to me it is focused on large bulk storage facilities that store and transfer flammable liquids, but do not consume/use them. That is not what I'm doing. Going through the various scenarios in Table 515.3 supports the aforementioned claim.

What do you think?

 

[ericwg]

Bump.

 

[rbalex]

I apologize for the late response. I had some personal activities I had take care of the last few weeks.
Some things to consider:

1. The title of an Article or Section is not necessarily “Code” per the NFPA Manual of Style.
2. The Scope of an Article is.
3. There are some magic “ands” and “ors,” in the Scope of Article 515 (Section 515.1). The product can be received in any number of ways AND stored OR blended for distribution in any number of ways.

Even if there is no intent to distribute the product in any manner, the Article applies. Other Articles, especially 514, may apply as well depending on the purpose of the fuel and the manner of its distribution. Tankage, unless specifically covered elsewhere, is subject to Article 515.

 

[gene6]

Good info!

 

[nhee2]

NFPA 58 Table 6.25.2.2 provides a pretty prescriptive table for LPG systems and area classification.

 

[ericwg]

I apologize for the late response. I had some personal activities I had take care of the last few weeks.
Some things to consider:

1. The title of an Article or Section is not necessarily “Code” per the NFPA Manual of Style.
2. The Scope of an Article is.
3. There are some magic “ands” and “ors,” in the Scope of Article 515 (Section 515.1). The product can be received in any number of ways AND stored OR blended for distribution in any number of ways.

Even if there is no intent to distribute the product in any manner, the Article applies. Other Articles, especially 514, may apply as well depending on the purpose of the fuel and the manner of its distribution. Tankage, unless specifically covered elsewhere, is subject to Article 515.

No worries. I appreciate the reply. First let me say I totally agree with the three points you made.

With regards to your last paragraph, as I mentioned in my OP, the purpose of these tanks is for one to provide fuel to an LPG standby engine generator and the second to provide fuel for gas-fired appliances, including but not limited to, a range, heat pump (HVAC), hot water heaters, and a pressure washer (in a vehicle wash building). The feeds from these tanks are via underground 2" PE. So, knowing the specific use for the LPG stored in these tanks and the method of distribution, can you please expand beyond "...may apply as well depending on the purpose of the fuel and the manner of its distribution"?

Thanks again!

 

[ericwg]

NFPA 58 Table 6.25.2.2 provides a pretty prescriptive table for LPG systems and area classification.

Yes, Table 6.25.2.2 provides good information on the extent of electrically classified areas, however, per Article 6.25.2.3 - "The provisions of 6.25.2.2 shall apply to vehicular fuel operations." FYI, Article 6.25.2.2 simply points to Table 6.25.2.2. Since my LPG does not support vehicular fuel operations, I don't think 6.25.2.3 applies.

 

[nhee2]

Yes, Table 6.25.2.2 provides good information on the extent of electrically classified areas, however, per Article 6.25.2.3 - "The provisions of 6.25.2.2 shall apply to vehicular fuel operations." FYI, Article 6.25.2.2 simply points to Table 6.25.2.2. Since my LPG does not support vehicular fuel operations, I don't think 6.25.2.3 applies.

Are you interpreting 6.25.2.3 to mean the table applies exclusively to vehicular fueling? I don't interpret it that way. I interpret 6.25.2.2 to say that the table applies to LP-Gas Systems within the scope of NFPA 58. And 6.25.2.3 to mean it ALSO applies to vehicular fueling stations. Although it is odd for them to specifically call that out.

Not to challenge what rbalex says but in my opinion NFPA 58 is the more applicable standard to use for this application.

 

[ericwg]

Are you interpreting 6.25.2.3 to mean the table applies exclusively to vehicular fueling? I don't interpret it that way. I interpret 6.25.2.2 to say that the table applies to LP-Gas Systems within the scope of NFPA 58. And 6.25.2.3 to mean it ALSO applies to vehicular fueling stations. Although it is odd for them to specifically call that out.

Not to challenge what rbalex says but in my opinion NFPA 58 is the more applicable standard to use for this application.

Yes, I am. Honestly, I don't think any "interpretation" is required. Is is very straightforward. First, it says it "shall apply to vehicular fuel operations". What verbiage in that sentence leads you to believe it applies to other systems? Second, if you look at the "Locations" listed in Table 6.25.2.2 and the "Extent of Classified Area" they sound like they pertain to fueling stations - outdoors, indoors, on piers and wharves, etc., geared towards fuel transfer. Third, and probably most important, 6.25.2.4 states "The provisions of 6.25.2.2 shall not apply to fixed electrical equipment at residential or commercial installations of LP-Gas systems or to systems covered by Section 6.26, which covers LP-Gas Systems on Vehicles. Thus, in my humble opinion and with all due respect I just don't see how this section of NFPA 58 applies to my situation. If you do, though, I would like to hear your justification.

 

[nhee2]

I had not seen 6.25.2.4 - that makes no sense to me.
I disagree that the table locations sound like they pertain to fueling stations only. Items A, D, E, F would/could all apply to fuel storage and supply systems depending on the size/scope. Even if not applicable code-wise, they provide a reasonable example for similar types of equipment that could be used as a basis for however you end up classifying your system.
At some point I assume your system transitions to a NFPA 54 system, so the table would only be relevant for the storage tanks and vaporizers (if you have them). if at all.