Compressed Natural Gas Stations - Indoor Equipment

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nhee2

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For those who have worked with CNG (Compressed Natural Gas Stations)
- How common is it for compressors to be located within a building vs. installed outdoors in a weatherproof enclosure?
- When they are in a building, how has the building interior been classified (Class I, Div 1 or 2)?
- Based on experience, would you consider a 'building' with one side open and three sides with exterior walls to within 4' of roofline to be 'indoors' or 'outdoors' when applying NFPA 52?
 
nhee2 said:
For those who have worked with CNG (Compressed Natural Gas Stations)
- How common is it for compressors to be located within a building vs. installed outdoors in a weatherproof enclosure?
- When they are in a building, how has the building interior been classified (Class I, Div 1 or 2)?
- Based on experience, would you consider a 'building' with one side open and three sides with exterior walls to within 4' of roofline to be 'indoors' or 'outdoors' when applying NFPA 52?
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- I've seen both configurations but neither were by my choice, rather it was process/mechanical designs.
- Both API (API RP500 and RP505) and AGA (XF0277) have recommendations. As usual, it will depend on size and ventilation. The API Standards have the advantage of being ANSI certified.
- I believe you meant NFPA 54. The API and AGA Standards address the effect of an "open" building. I believe the API Standards are more comprehensive but you have to dig through a lot of text.
 
rbalex said:
- Both API (API RP500 and RP505) and AGA (XF0277) have recommendations. As usual, it will depend on size and ventilation. The API Standards have the advantage of being ANSI certified.
- I believe you meant NFPA 54. The API and AGA Standards address the effect of an "open" building. I believe the API Standards are more comprehensive but you have to dig through a lot of text.
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Rbalex,

- The building design in this application is not ours.
- NFPA 52 provides requirements for area classification of CNG facilities. It also has requirements for 'indoor' and 'outdoor' areas, although it does not explicitly define criteria for when sheltered area might be considered 'outdoor'.
- The AGA standard you reference does provide some guidance for compressor buildings (I assume geared towards pipeline compressor stations) and says that where 50% or more of the wall is open, it could be considered adequately ventilated.
- In the '3-sided building' case, even with a 4' opening at the roof line (conceivably to prevent the collection of any gas), I have suggested the building does not meet the criteria for 'outdoor'.
- This has created a problem because the compressor packages installed are listed as Div 2 and without any documented calculation of ventilation (natural or mechanical) in the building, I don't think the building is a Div 2 area. But could be wrong.

I have not looked at API RP500, and will take a look there.

Thanks
 
I did check with the mechanical engineers to ensure that there was adequate ventilation and no dead air spaces in the design. You will probably find that with the design as you have described it that it is indeed a Division 2 location. One open side that represents at least 25% of the perimeter makes a big difference.
 
rbalex said:
I did check with the mechanical engineers to ensure that there was adequate ventilation and no dead air spaces in the design. You will probably find that with the design as you have described it that it is indeed a Division 2 location. One open side that represents at least 25% of the perimeter makes a big difference.
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Thanks.

In fact, NFPA 52 specifies 'mechanical ventilation' as a requirement for indoor installations. I would have preferred they not put walls around the area, to allow an easier designation of 'outdoor' for the installation.
 
nhee2 said:
Thanks.

In fact, NFPA 52 specifies 'mechanical ventilation' as a requirement for indoor installations. I would have preferred they not put walls around the area, to allow an easier designation of 'outdoor' for the installation.
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Review API RP500, especially Section 6.3. You may be surprised how little it takes to achieve "adequate ventilation" especially with lighter than air gases. See Figure 105 with its accompanying text [Section 14.3.8] as a typical example. There are other sections that deal specifically with compressors.

Note: NFPA 497 recognizes API RP500 may be more appropriate for larger facilities.

PS You may want to also review the definition of ventilation, adequate ​in RP500.
 
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NFPA 497 defines adequate ventilation in its "natural order". It's also easier to understand.

Theoretically, both API RP500 and NFPA 497 ultimately derive their definitions from NFPA 30 - which doesn't formally define it at all. Gotta love it. I've known (and forgotten) this for years; it fries my brain on occasion to research this hazardous (classified) locations business.
 
rbalex said:
NFPA 497 defines adequate ventilation in its "natural order". It's also easier to understand.

Theoretically, both API RP500 and NFPA 497 ultimately derive their definitions from NFPA 30 - which doesn't formally define it at all. Gotta love it. I've known (and forgotten) this for years; it fries my brain on occasion to research this hazardous (classified) locations business.
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AND - NFPA 52 does not require 'adequate ventilation'. It specifies 'mechanical ventilation'.

I thought that natural circulation through a building was reliant on differential temperature between inside and outside (this may be wrong). In my open, 3 sided building example, not sure that this differential temperature will be there.
 
To be blunt, I don't believe your application as you have described it is within the scope of NFPA 52. I've reread it several times; but, if you insist on force fitting it, then go ahead and declare it Division 1, it will be safe (which is all I care about) and you're only wasting time and money.
 
rbalex said:
To be blunt, I don't believe your application as you have described it is within the scope of NFPA 52. I've reread it several times; but, if you insist on force fitting it, then go ahead and declare it Division 1, it will be safe (which is all I care about) and you're only wasting time and money.
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I've probably confused the issue then in attempting to describe the application.

It's a CNG station for fueling vehicles. Although NFPA 52 is titled "Vehicular Gaseous Fuel Systems Code", Chapter 7 (of 2013, I think this moved in 2016) is specific to the compression/storage/dispensing facility systems. Are you saying you typically apply NFPA 54 to this type of facility and not NFPA 52?
 
nhee2 said:
I've probably confused the issue then in attempting to describe the application.

It's a CNG station for fueling vehicles. Although NFPA 52 is titled "Vehicular Gaseous Fuel Systems Code", Chapter 7 (of 2013, I think this moved in 2016) is specific to the compression/storage/dispensing facility systems. Are you saying you typically apply NFPA 54 to this type of facility and not NFPA 52?
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Compare their scopes.
 
rbalex said:
Compare their scopes.
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The fuel gas code says max pressure of 125 psia. Although the 'exclusions' only 'exclude' CNG as it applies to on-board fuel systems in 1.1.1.2(15).

Still seems to me that NFPA 52, Chapter 7 (in 2013) is the applicable code.

Regardless, your input on the feasibility of concluding a Div 2 area vs. a Div 1 area based on the 'adequate ventilation' is appreciated - that's what I was looking for. Thanks.
 
You are the one that is responsible for the electrical design and I do not want to in anyway undermine your authority. It is your judgment, not mine, that must go into evaluating the situation. While I personally don't see the applicability of NFPA 52, unless I believed it would result in an unsafe installation, as a PE, I would support you.
 
To be honest, if I had known from the beginning it was a fueling application I would have probably gone straight to Article 514 and not looked back. Well, I might have consulted NFPA 30, 55, or 497 or API RP500. NFPA 52 isn't one of the Standards listed in Section 500.4(B) IN No. 2 so I would have ignored it. In fact, it isn't referenced anywhere in Articles 500 to 516 as applicable to hazardous locations at all.

I confess I wasn't familiar with NFPA 52, but what you described still isn't within it's Scope (Section 1.1) or Purpose (Section 1.2). I am however, quite familiar with several CNG, LPG and SNG facilities.

I took some time reviewing NFPA 52 (online) as a whole. I'm certainly not yet fully conversant, but it looks pretty solid for overall mechanical operation/installation requirements. I don't believe I would make indoor storage the general basis for my understanding of classifying hazardous locations though; in fact, is requirements for ventilation and gas detection aren't generally consistent with more common standards. Truth is the gas detection scheme, if used, may run afoul of NEC Section 500.7(K).

If I used it, I would probably base operating mechanical ventilation under NFPA 496, Type Y. I personally prefer passive; i.e., "natural" ventilation - that's why I talk to the Mechanical/HVAC team.
 
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