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Separation Distance Between Generator and Building

Separation Distance Between Generator and Building

Separation Distance Between Generator and Building

Hi All,

I am trying to establish seperation distance requirements between a Generator (outdoor) and a Building.

The 2MVA generator has a 3000L diesel fuel day tank (790 US Gal). The tank is integral to the generator package and located beneath the engine.

The building exterior wall does not have any fire resistance.

NFPA 37 (4.1.4) specifies a separation distance of 1.5m (5ft).

I have also checked NFPA 110 (5.6.1), which refers back to NFPA 37.

I have also looked at NFPA 30, with respect to the size of the fuel tank. Table 15.3 provides separation distances for outdoor storage. However, I believe that the integral fuel tank on the generator cannot be classified as a 'drum', a 'protable tank' or an 'intermediate bulk container'.

In which case my conclusion is that 1.5m is the required seperation distance.

Any comments?


RE: Separation Distance Between Generator and Building

2mVA is a big boy generator. When i have dealt with these larger gen sets in the past for large plants they were in their own detached building, not outside. These usually have double walled, belly tanks as you note, and quite a few alarm systems as well. I have not delved in to the code aspects on these, but they are inherently fairly safe for that reason. If this was located inside the building, next to people and things, you would have some very different issues to contend with as you probably know.

RE: Separation Distance Between Generator and Building

My answer is "Ask the local AHJ."

My last place of employment had a generator about that size, a Cat with a nice sound-reducing enclosure and 2500 gallon skid-mounted, double-wall tank underneath. Local codes dictated 5 feet away from building, but I'm not sure the wall type had anything to do with it. Our walls were concrete. I don't think it makes any difference, though.

There are some mighty knowledgeable specifier/regulator folks in this forum, wait a bit for their opinion.

Best to you,

Goober Dave

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RE: Separation Distance Between Generator and Building

there is a section that covers exhaust, that makes the set back further than any other requiremetn, will have to look for it

RE: Separation Distance Between Generator and Building

First let me define what you have. It is an atmospheric aboveground storage tank. It's not a container, and it's not a portable tank, drum, vessel or intermediate bulk container - it is an atmospheric AST, and must be constructed to UL 142.

NFPA 37 is a unique standard because it only governs for tank volumes up to 660 gallons. Your tank volume is greater than this volume so NFPA 37 defers you to NFPA 30.

Tank siting requirements are found in Chapter 22 of NFPA 30, 2012 ed. for a 790 gallon fuel tank. In NFPA 30 one must apply two tables for storage tanks. The first table establishes your separation requirement from certain exposures based on your tank size and the capability of your local fire department. The second table establishes your separation distance based either on tank volume or diameter. You are dealing with a shop fabricated AST so the separation distance is based on volume because I highly doubt your tank is round - its most likely rectangular, especially if this is a sub-base tank.

For a 790 gallon AST, NFPA 30 Table requires the separation distance for an atmospheric AST to be based on Table (b) if you have a fire department capable of providing protection from an exposure fire to a tank. If you don't have this, 2X the value I will inform you of:

Distance to a property line that is or can be built upon: 15 feet
Distance to the nearest important building on the same property: 5 feet

What's an important building? Answer: Not your decision. It's up to the local code authority. Is the fire department capable of providing protection from an exposure fire to a tank? Answer: Not your decision. It's the decision of the local code authority.

RE: Separation Distance Between Generator and Building

Thanks everyone for the helpful comments.

I am now better informed when I present to our AHJ.

As we have an industrial fire brigade on site, I hope our AHJ will agree that 'protection for exposures' is available.

Can someone clarify for me why the separation distance is different for an 'important building on the same property'(5ft) and a 'property line that is or can be built upon'(15ft). Does this mean that if the building is your own, you can locate the generator closer to it, as compared with a building that is on someone else's property?


RE: Separation Distance Between Generator and Building

Two items

Five feet from a building

Fifteen feet from your neighbor/ property line, so you do not impose on your neighbor

RE: Separation Distance Between Generator and Building


NFPA 30 allows you to assume a greater risk on your property. As a result you can place the atmospheric AST to a building on your own property rather than at the property line. You still need to provide some separation so your plant fire brigade can protect exposure structures or process equip,emt.

The closer the astmospheric AST is to the property line the greater the risk to your neighbor or community. It also increases risks to firefighters because their response may be delayed while roads are being closed. Stretching a 1 3/4-inch handline on a busy roadway with every driver looking at the fire, or their phone figuring out how to make a video of the fire so they can twitter it increases the risks to firefighters.

RE: Separation Distance Between Generator and Building

Many thanks Stookey.

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