OK to Locate Diesel Fire Pump Fuel Tank Outside?

3/6/2025

Does anybody have experience with locating diesel fire pump fuel tanks in exterior locations where the local ambient temperature can drop to below freezing point?

We have an unavoidable situation where we have to locate the fuel tank outside the pump room and we're hoping not to have to build a heated enclosure. NFPA 20 seems to require a heated enclosure, but FM not so much.

I am aware that condensation and fuel deterioration are issues to be dealt with, but I was thinking maybe good quality thermal lag of the tank and feed/return fuel piping may be sufficient with just a roof structure above the fuel tank.

What are your thoughts on this?

any thanks in advance for your thoughts and advice

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9 Comments

Pete H

3/6/2025 06:48:37 am

Regardless of code, I'd say you really want a heated enclosure. Diesel fuel in freezing temperatures can become more waxy/gel like and cause clogs and other problems when using the fuel.

Dan Wilder

3/6/2025 07:40:57 am

So NFPA 20 (19') is clear it shall be inside and even go as far as saying "if possible" - 11.4.3.2

FM 3-7 Section 2.4.21.3 Locate diesel fuel storage tanks inside the pump room. Extend the tank fill and vent lines outdoors.
If they cannot be located in the pump room, provide a reliable means of maintaining the fuel storage tank
temperature above 40°F (4°C).

I would not rely on thermal lag to maintain that 40°F temperature for the tank and the supply and return lines. Can it be done, possibly with heat trace & insulation and likely very close tabs of both the temp and the fuel useability as the tank will be going though daily temperature swings so fuel fills and vents will all have the potential for condensation leaking back into the tank.

Glenn Berger

3/6/2025 08:18:25 am

I would not consider locating any of the fire pump related equipment outdoors. The unpredictability of the weather makes any consideration of maintaining diesel fuel conditions in an exterior environment a bad choice. In addition to maintaining the diesel fuel, you need to maintain the fuel tank itself.

Jesse

3/6/2025 08:36:18 am

Very much not recommended. The only time I've seen fire-pump diesel tanks outside was in CA and Central America when the entire fire pump system was outside.

If it cannot be inside for some reason, you're going to need to provide a reliable means to keep it >40°

Todd E Wyatt

3/6/2025 08:43:40 am

If the fuel supply tank(s) for the pump are located in a zone where freezing temperatures are possible, the fuel supply tank(s) shall be locate IN the pump room per NFPA 20 as required by the scoping Code (e.g. IBC).

REFERENCES

IBC-2024
Chapter 9 Fire Protection and Life Safety Systems
Section 913 Fire Pumps
913.1 General
Where provided, fire pumps for fire protection systems shall be installed in accordance with this section and NFPA 20.
Exception: Pumps for automatic sprinkler systems installed in accordance with Section 903.3.1.3, or Section P2904 of the International Residential Code.
913.3 Temperature of Pump Room
Suitable means shall be provided for maintaining the temperature of a pump room or pump house, where required, above 40°F (5°C).

NFPA 20 -2025
11.4.3* Fuel Supply Tank Location.
A.11.4.3
Diesel fuel storage tanks preferably should be located inside the pump room or pump house, if permitted by local regulations. Fill and vent lines in such case should be extended to outdoors. The fill pipe can be used for a gauging well where practical.

Enhanced Content
Where diesel fuel storage tanks are located outdoors, NFPA 30, Flammable and Combustible Liquids Code, should be consulted for separation requirements between the pump room structure and the tank. When tanks are located outside they should be insulated for protection against changing temperatures, have a heating system installed if necessary, and be light in color to reflect radiated heat from the sun. Changing temperatures cause the tank to breathe through the vent pipe and bring in humidity, causing the formulation of water, which promotes the growth of microorganisms.
It is preferred that the tank be located in the pump room, especially in colder climates as the diesel fuel can gel and create engine operational issues. If the tank is located in an area where temperatures of 32°F (0°C) are experienced, the tank must be located in the fire pump room, which is required to be maintained at the minimum temperature recommended by the engine manufacturer. See 11.6.5.

11.4.3.2
In zones where freezing temperatures [32°F (0°C)] are possible, the fuel supply tanks shall be located in the pump room.

Jose Figueroa

3/6/2025 08:53:16 am

I have seen outside gravity fuel tanks in North Michigan and Hinton, Alberta.

NFPA 20 and FM DS 3-7 are essentially the same code. In these places, you need reliable means to heat the pump house anyway.

DS 3-7 shows this: “ 2.4.21.3 Locate diesel fuel storage tanks inside the pump room. Extend the tank fill and vent lines outdoors. If they cannot be located in the pump room, provide a reliable means of maintaining the fuel storage tank temperature above 40°F (4°C).”

The trick is in the words “reliable means”.

Jack G

3/6/2025 09:17:23 am

When I started in the industry in the 60 s , diesel fuel tanks could be installed outside ( Delaware, Md, NJ, Pa )
Thru the years this changed. The rules are such for a reason, and you must explain to the customer why this is so. It should be an easy sell, unless the engineer/ customer/ AHJ is making this your problem ( the heated enclosure ) ( to build a heated enclosure for the tank).
I ve installed diesel tanks on stilts above the discharge and or pump supply before. The legs are roughly 2 ft and or 4 ft on center, about 2 ft high. So straddle the bfp, or fp discharge, and place the tank higher in the fire pump room, between joists or something like that. You do have a big ole muffler with insulation in there too.
When the legs are longer than 2 feet, approved bracing must be added for the legs as 2 inch legs could buckle. A 5 foot bottom of tank should be doable and or acceptable. ( double wall tank, so no dike is required )

Jack G

3/6/2025 09:27:21 am

I also can remember in the early days when not only diesel fuel tanks but mufflers were installed outside ( ISO, FM, IRI, ) .
This has changed thru the years also and it has been found to be a good thing.

Zach H

3/6/2025 01:54:18 pm

External tanks are incredibly common with a recirc pump or fuel heater, sometimes both for fire pumps.

OK to Locate Diesel Fire Pump Fuel Tank Outside?

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