15-0205 v2.1/Potomac Watershed Study Center, Grass Building/Combustion for Life Safety in Rural Locations


Combustion is included in the design for Hard Bargain because we have a fire pump and because the local electrical service is not sufficiently reliable.

Our property is protected by a sprinkler system for two reasons:

The facility involves overnight dormitory accommodations
The facility is located in a rural area and the likely delay in response from a fire company is beyond the owner’s risk tolerance.

The owner’s campus is served for potable water by a well. The well system does not provide adequate pressure or volume to supply the sprinkler system on its own, necessitating a fire storage tank and means of pressurizing the water. We examined the feasibility of locating a tank at a sufficient height to provide the required water pressure as static pressure without energy input during a fire event. However, our property is within the viewshed of Mt Vernon, and is prohibited by statute from development that impacts the view from George Washington’s historic home. Our building heights are coordinated to remain beneath the vision plane from Mt Vernon. However, any tank installed at sufficient height to pressurize the sprinkler system would necessarily have been above this plane and within the viewshed of Mt Vernon. This prohibited us from installing a fire tank at the necessary height to provide static water pressure to the buildings and required us to pressurize the fire system with a fire pump.

Once we determined a fire pump was necessary, we needed to decide between an electric motor-drive fire pump and a combustion-engine driven fire pump. The power supply to an electric-motor driven fire pump is governed by the attached sections of NFPA 70, the National Electric Code. If the design calls for the fire pump to be served only with electric power derived from the utility, then the utility must indicate that its power meets the standard for reliability indicated in the attached. As we are located in a rural area and our facility is served by a single utility circuit, this is not possible. Therefore, an on-site backup source must be considered.

Once we have an on-site backup source, our choices are a combustion generator serving an electric-driven pump or a combustion engine-driven pump.
We examined the possibility of dedicated batteries, storing power from the on-site PV system, but rejected this due to the environmental hazards associated with such a large battery installation, the penalty to our photovoltaic system of having power dedicated to the emergency uses, and the regulatory complexity of serving a fire pump with an non-recognized electrical infrastructure.
Thus we concluded that on-site combustion was required for our rural site to provide the necessary fire protection to meet the owner’s project requirements and code-driven life safety requirements.
We also examined the difference between a combustion-engine generator feeding an electric-motor fire pump and a combustion engine-driven fire pump. The electrical code requires a generator feeding a fire pump to be able to satisfy the locked-rotor amp current of the pump motor continually. This requirement means that the engine on a generator would be roughly 6 times larger than the required engine on an engine-driven fire pump for the identical pump load. This would elevate the emissions profile of the generator-electric pump combination; for this reason, we concluded that a combustion-engine driven fire pump was the most appropriate solution for our facility.

Based on the reasoning above we would request we be granted an exception for the use of the combustion engine driven fire pump as related to life safety on our project.


Exception I07-E6 4/2010 Emergency Power Systems allows for the use of combustion based emergency generators. A combustion engine drive fire pump for emergency use is comparable to a generator and therefore would be allowed under this existing exception.

Post ID 2525

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