It’s not every day a client approaches you asking for assistance in complying with its insurance carrier requirements by providing a tank of water. However, that is exactly what happened in September 2022 for a confidential client whose campus needed a major upgrade to keep the fire protection systems up and running.

The campus is a research and development facility comprised of 11 total laboratory buildings and other support buildings such as an electrical block house, security and administration building, mechanical boiler/chiller/cooling tower plant, and more.

The campus has an existing 1,000 gallons per minute fire pump serving an underground fire protection loop the buildings on campus connected to for their fire protection needs. The loop also served various fire hydrants on campus.

The pump receives its water from a 10-inch municipal water main along the south end of campus. Unfortunately, if this fire pump were ever to be tested at 100% capacity, the suction pressure would drop to almost 0 pounds/square inch (psi), creating serious concerns for the campus and the insurance company.

The need was to provide a second water source for the campus fire protection system. Because the municipality had limited resources available to add a second pressurized water service, the solution became a storage tank. After doing some quick math on system flow and required service run time, this turned out to be a 250,000-gallon water storage tank.

Because a tank like this is atmospheric, a new fire pump would be needed to feed the water to the pressurized loop. The new fire pump will need a home as it cannot be placed in the water tank. That meant a pump house must be built to contain the fire pump and its supplemental equipment.

Another important topic was the interruption to the existing underground loop. The downtime must be minimized as much as possible to reduce risk for the campus.

Design Considerations

With those major decisions made, many specific considerations needed to be accommodated during the design of this project. Where would the tank go? How would it be serviced? How would the structures be secured? How would the tank be filled, and how quickly would it need to be filled? 

To start the process of finding a home for the tank, a civil engineer was brought in to analyze the topography of the campus. It might sound obvious, but the first areas under consideration were some large, open areas. However, it’s not that simple to drop a tank of this capacity anywhere you might think it fits.

A utility-locating company ensured no underground utilities would end up under the proposed location. A geotechnical engineer was needed to take borings of the location to help determine the structure and foundation of the tank. The topography was used to determine the flattest spot in the area being considered to reduce the amount of excavation and re-grading, which is a very expensive and time-consuming endeavor.

Once the tank location was identified, the orientation of the pump house was next. The pump house needed to abut the tank to allow for piping connections but could realistically be located at any angle around the tank’s perimeter. 

Due to soil conditions, there would be considerable settlement of the tank compared to the pump house unless significant preparation was done under the tank to bear the weight of the water. While some can be accommodated, what was expected without any prep work would be unacceptable to design around.

Other considerations for the tank and pump house extending beyond a normal project were design wind speed for the tank structure, snow load for the tank roof, seismic design criteria, cathodic and lightning protection, tank insulation, freeze protection and tank level monitoring. 

Electric Vs. Diesel Fire Pump

As mentioned earlier, 250,000 gallons of storage is needed to meet National Fire Protection Association (NFPA) requirements; this number is derived from minimum flow and run-time requirements. NFPA also regulates the time it takes to refill the tank from empty, which is a maximum of eight hours. 

For the pump house, the team needed to coordinate the use of a diesel or electric fire pump, determining the sequence of primary, backup and jockey pumps with the new design and existing pumps on site.

Because of the flow rate and pressure, the load for an electric fire pump was too high to be practical related to what was available on campus in the area. Therefore, a diesel pump was chosen. This forced several other design considerations for the pump house, such as combustion air intake, diesel exhaust, room exhaust/ventilation, maximum interior temperature and fuel storage/fill.

Because this is a fire protection system, all these items must have a level of redundancy to them and support the operation of the diesel fire pump. The room cannot get too hot such that it will shut down the diesel engine; the exhaust fans and tank heating elements must still operate in the case of a power loss, and the alarms must be tied into the campus fire alarm system to notify of operation.

The irony in the project proceeding with a diesel fire pump is that a diesel generator was needed to provide the emergency power required to maintain operation of all the supporting components. NFPA does not allow a diesel fire pump to be its own emergency generator. The good news is it’s a much smaller emergency generator than if the fire pump was electric.

The controls and freeze protection of the water in the tank are straightforward. The tank fill is manual, so it’s simply a low level and full indication of the amount of water in the tank. What was most surprising was the amount of heat required to keep the tank from freezing — only 18 kW. There are also alarms for if the water temperature falls below 40 F and when the tank temperature is restored to above 40 F.

All in all, the design of this project was an amazing learning experience. Being able to solve an uncommon problem with a relatively straightforward solution was something I won’t forget. And ultimately, the campus will be safer now due to the 250,000 gallons of water sitting in the far corner of campus. 

James Dipping, PE, CPD, GPD, LEED AP BD+C, ARCSA AP, is principal of operations for technical support services and discipline leader for plumbing engineering at ESD now Stantec, with more than 27 years of experience in the plumbing design and construction industry. He is co-author of the American Society of Plumbing Engineers’ “Engineering Methodologies to Reduce the Risk of Legionella in Premise Plumbing Systems,” as well as an industry speaker.