How to Design a Life Safety Generator Fuel System

Design Guide ESDG 611

Life Safety Generator Fuel Systems can be complex. They need to operate reliably and meet applicable building codes. The configurations are often dictated by the very limited space available in the building design. To make them easier to understand we break down the design process adding elements as needed to accomplish your design goals. Each Step results in a functional system, so you can just stop after the step that fulfills your requirements.

How Much Fuel is Needed

A life safety generator is a requirement of many building codes. It is meant to keep the lights on and the elevators working for a minimum of 2 hours to allow people to get out of the building. These are usually smaller generators 100-1000 KW with limited fuel storage needs. A 1000 KW generator at full load consumes about 75 Gallons (300L) per hour, so 2 hours is only 150 Gallons (600L).

The tank storage requirement is based on a 75% full tank, so you would need 150 / 0.75 = 200 Gallons (800L). Then add 10% because only fill to 90%, and another 10% considered unusable at bottom of tank. This would mean a 250 gallon (1000L) tank.

If the generator is above the lowest level in the building then the building codes will limit the amount of fuel that can be stored at that level. This is often limited to 60 gallons (240L), so the day tank capacity at the generator may be 50 gallons (200L), with the rest of the storage capacity in the tank in the basement.

Step 1a: Basic Tank and Accessories (Day Tank)

The first step in setting up a fuel system is to install a basic diesel storage tank and its necessary accessories. An optional containment tank is shown (item 2), but is not needed in some cases. This tank can be located directly next to the generator, in another room, outside, or can even be built as the base of the generator (called a sub-base tank). See Earthsafe's day tanks under the M5 series tab 


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Step 1b: Add Direct Fill Accessories

To fill the tank with diesel, a direct fill port is added. This accessory is equipped with a spill container and a mechanical overfill valve - to prevent overfilling of the storage tank.

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Step 1c: Add Basic Sensors

For the storage tank to be controllable, add sensors to the tank. Common accessories include leak sensors, high and low level sensors, and a level transmitter. These accessories can be monitored by Earthsafe's C8 control panel, and this data can be sent to the buildings BMS system as well. Information on Earthsafe's C8 and C1 controllers can be found under "Fuel and DEF System Controllers"


*Points to Monitor

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Step 2a: Add Remote Fill

If the generators are inside buildings, a remote fill connection to the outside is needed. Typically the standard, and sometimes emergency, vents are moved to the building exterior. See Earthsafe's M4 series fill stations


*Points to Monitor

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Step 2b: Add Remote Fill – 2 Tanks

The fill station can be specified as multi-tank to fill more than one generator tank *Points to Monitor

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Step 2c: Add Remote Fill with Pump

Generators inside buildings may be at an upper level and a Pump Fill Station may be specified. Consider:

  • The pump can usually have modest flow rates, 20-25 GPM (80-100 LPM) since the life safety tank sizes are limited.
  • Rooftop generators may require high pressure pumps with larger HP (KW) motors.

*Points to Monitor

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Step 3: Add Filter Polisher

A filter polisher is added outside of the storage tank to remove water and other contaminants from the diesel fuel. This helps prevent clogged fuel lines and engine damage, which can lead to generator failure. Learn more about Earthsafe's filter polishers under the M3 series


*Points to Monitor

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Step 4a: Receive Fuel into Storage Tank, then Transfer to Day Tank

Generators inside buildings may require storage tanks in addition to day tanks. Run times may require fuel in excess of day tank capacities

  • Fire Codes limit on fuel tank volumes above lowest building level.
  • Multiple Generators in Building may need fuel from a single storage source


  • Fire Stop and fusible link valves at floor-wall penetrations.

See Earthsafe's M6 series storage tanks 


*Points to Monitor

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Step 4b: Receive Fuel into Storage Tank, then Transfer to Day Tank

** Fuel Room Classified Area**

The Fuel Room may be a classified electrical area by local code – or entry may be considered a safety hazard.

Move the pumps and controls outside the room to an (a) ordinary electrical area that (b) is accessible to users.


  • Fire Stop and fusible link valves at floor-wall penetrations.
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Step 5: Add the Day Tank Equipment at the Generator Locations

Day Tanks, or sub-base tank refill equipment is installed at the generator locations inside the building or at rooftop.

Control can be by Local Controller or by the master controller at the storage tank. See Earthsafe's C8 and C9 master controller


*Points to Monitor

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