Diesel Power

Codes and standards related to emergency generator fuel tank storage differ from one jurisdiction to the next, and accepted location of a tank is one of the major variables.

In Chicago, for example, while the generator itself may be stored in a building's parking garage, the generator's diesel fuel tank may not. "You cannot store the fuel in the parking garage structure, even though it's counter to what happens in the parking garage; you have cars with fuel tanks parked there," says Anil Ahuja, P.E., senior vice president with CCJM Engineers, Ltd., Chicago.

Besides concerns about a car's ignition being potentially dangerous when in close proximity to a fuel tank, the risk of an automobile crashing into a tank is another reason for keeping them out of the garage. Instead, the tanks are mandated by local code to reside on the lowest level of the building above the garage. Ahuja notes they aren't allowed any higher, because "if the building falls, you don't want the generator to fall with it."

Chicago's code is in variance with NFPA 110, Standard for Emergency and Standby Power Systems, in that the city, unlike the standard, doesn't allow automatic shutdown of life-safety generators, even in the case of an emergency. This is not allowed, as the city code argues it's very likely that the generator will need to be used during the emergency. "What if someone shuts it down by mistake?" asks Ahuja. "They would basically be shutting down the emergency generator that is required for life safety. When the power goes off in a high-rise building, these are the only generators that provide power for egress for people to find their way out." However, other cities do allow for automatic shutdown, citing the need to cut off the fuel supply in the case of a fire. NFPA 110 is updated every two years, and its next revision is scheduled for the fall of 2004.

Perhaps the most significant change in emergency fuel storage policy to come about recently is the introduction of the Underwriters Laboratory (UL) 2085 standard, Special Purpose Flammable Liquid Tank Protected Secondary Containment Generator Base Tank (see CSE supplement On Peak Performance 11/02 p. 8). The majority of above-ground tanks in use today were designed to UL 142 specifications, which came about in the 1920s and '30s, and in accordance with NFPA 110 and NFPA 37 (Stationary Combustible Engine and Gas Turbines). While UL 142 mandates a steel inner tank and a steel secondary tank, UL 2085 adds the safety of lightweight thermal concrete jacket that surrounds the inner tank.

The tank's popularity is spreading. According to William Hall, consulting engineer with DWX Tank Co., Dallas., only 5% of all generators currently being manufactured are geared toward UL 2085. However, while only two or three companies manufactured UL 2085 tanks in 2000, he says, more than 100 firms are building them today. Among the cities that have adopted UL 2085 are Houston, Atlanta and Phoenix.

Unlike UL 142, UL 2085 tanks are tested for ballistics and automobile impact. Plus, Hall notes, "They meet or exceed all fire codes throughout the U.S."