Genset Belly Tank installation

[TMEldridge]

Client wants to install two gensets in one housing. This would mean we would have two belly (aboveground subbase) tanks side-by-side inside the housing. I cannot find any way to get around NFPA 30 requiring 3 ft separation (both tanks are greater than 660 gal and less than 3,000 gal). How can side-by-side belly tanks be installed, literally side-by-side, without violating NFPA 30?

 

[stookeyfpe]

First, are the tanks inside or outside a building? From the description, it appears the tanks are located outside of a building.

The standard that governs the installation of stationary combustion engines is NFPA 37. If the tanks are installed in accordance with NFPA 37 and are located outdoors, section 6.3.3 (2002 edition) requires spacing in accordance with NFPA 30. NFPA 37 does not contemplate a condition such as explained. If the tanks are located inside a building, tank shell-to-shell separation distances do not apply. See NFPA 37, section 6.3.2.

If the aboveground storage tanks are outdoors I would suggest an equivalency using section 1.4 of NFPA 37. You may be able to demonstrate that your design offers additional safeguards or safety features that can be used to eliminate the separation distance requirement in NFPA 30, sec. 4.3.2.2.1. One equivalency is to provide overfill protection on the tank fill connection, which limits the potential for a fire resulting from an overfill. Spill containment basins at the tank fill connection could also be considered so in the event of an overfill, the spill is contained. Be careful on this because I have seen overfilled tanks discharge product through the tank emergency vent. Another concept for equivalency (although not popular) is to provide a water mist or dry chemical fire suppression system in the enclosure. This could be shown as equivalency to the < 3 ft. shell-to-shell clearance. Any equivalency requires the approval of the authority having jurisdiction.

I've reviewed plans and inspected multiple generator sub base tanks but have never seen two generators in one enclosure. Does the owner realize that putting two generators in one enclosure would likely mandate lock-out/tag-out protect the generator technician, which then negates any standby / emergency power? A little more detail please.

 

[TMEldridge]

The tanks are outside the building.

What is Section 1.4 of NFPA 37. I have 1994 edition, which may be the problem. The tanks will be equipped per NFPA 30 secondary containment requirements (high alarm, anit-siphon, etc).

 

[stookeyfpe]

The section I am quoting is titled "equivalency." NFPA standards have always had a statement that allows an alternative method of preparing a design so long as the intent of the code is met.

When an equivalency is proposed, you must demonstrate that the design is equal or greater than that specified in NFPA 30. I noted in your most recent post you have an anti-siphon valve. Does your design incorporate a main storage tank that pumps fuel to the generator sub base tanks? If so, I would consider increased separation distances from buildings and property lines as an equivalency to the tank-to-tank shell spacing.

Also, have you discussed any of this with the local fire official or facility health and safety professionals? They will want to review the equivalency.

 

[TMEldridge]

I did locate the equivalency section in NFPA 30. Thank you.

There are 18 gensets on site (9 pairs) with belly tank for each. No AST or UST is used to provide backup fuel to the belly tanks. This is for an industrial facility. We have exceeded the tank-building separation and genset pair-to-genset pair distances. Hopefully, these separations will be adequate to satisfy the fire marshall.

We plan on meeting with the fire marshall soon to review prior to submittal.

 

[stookeyfpe]

In my mind the design demonstrates equivalency due to the increased separation distances. Plus, if a fire involves one generator array and extends to both tanks, the NFPA 30 required minimum 3 foot shell-to-shell separation is not going to offer the firefighters any assistance because of the shielding by the single equipment enclosure.

Good luck.

 

[TMEldridge]

I appreciate all your input. Thanks!