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June 2, 2017
- Fire Safety/Protection
By Brian Buscher
One of the fastest elevators in the world carries passengers up to the 124th floor observation deck at the Burj Khalifa in Dubai in about one minute. Unbeknownst to most who tour the world’s tallest building, there’s a separate “fireman’s elevator” — the longest-traveling service elevator in existence and just one of the fire safety components of the 160-story, 2,716-foot architectural and engineering marvel.When buildings exceed 400 to 500 feet, higher floors are often beyond the pumping capacity of fire departments, which could result in loss of life or property in the event of a fire. Fire pumps are an essential component of water-based fire protection systems. It is vital that they are designed and installed properly; otherwise fire protection systems may not function correctly. And nowhere is the reliability of fire pumps more critical than high-rise buildings, where the evacuation of the building occupants may not always be feasible if a fire starts.The 2016 edition of the NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection, includes new rules that specifically address fire pumps installed in high-rise buildings, with the intent of standardizing fire pump design in these types of structures to ensure an appropriate level of reliability.The NFPA 20 Technical Committee on Fire Pumps developed specific provisions regarding the fire pump and water supply arrangement. Under the new requirements, even if a single piece of equipment becomes impaired, the full fire protection demand of the building can still be met.One of the most significant changes in fire pump design for high-rise buildings is that fire pumps operating in a series can no longer be located on different floors unless some very stringent criteria are met to ensure safe operation of all pumps. The practice of vertical staging — placing the second and third fire pump in series on higher floors — requires that the discharge pressure from the lower pump be sufficient to feed the pumps on the higher floors. Consequently, if the fire pump at the lowest level fails, the rest of the fire pumps in series will also fail for lack of adequate suction pressure.
Under the new NFPA 20 provisions, fire pumps in series must be installed in the same pump room. This modified fire pump design increases the reliability of the overall fire pump operation. When the pumps are located on the same floor, failure of a lower level pump will no longer result in cavitation and damage to the higher-level pumps that it feeds. In the updated arrangement, if the first pump in series fails, there would still be significant enough pressure to the other pumps in series to pressurize the system. NFPA 20 18.104.22.168 states that no more than three pumps shall be allowed to operate in series as a part of a series fire pump unit. Locating fire pumps in series in the same pump room provides additional options for firefighters to pump water into building sprinkler systems and reduces the complexity of fire department connection. In addition, it simplifies fire pump maintenance and restores fire pumps in the event of an emergency during maintenance.
More reliable fire pump operation isn’t the only reason for requiring fire pumps in series to be in the same pump room. The new requirement also ensures firefighters can safely respond and assess pump operation during a fire in accordance with NFPA 20 standards. When responding to an alarm, firefighters go immediately to the pump room to make sure equipment is operating properly. When pump rooms are on multiple floors, it increases the risk for firefighters, who must take elevators or stairways to access pump rooms — which can put them in harm’s way if they encounter smoke, the fire itself, or other issues.
The code does still permit vertical staging, but only if the NFPA 20 provisions that protect firefighters are incorporated into the design of the fire protection system.Although there are considerable benefits to requiring fire pumps in series to be housed in the same room, the NFPA 20 Technical Committee acknowledges that there are exceptions. The 2016 edition of the NFPA 20 clarifies five conditions under which fire pump units are permitted to be in separate pump rooms:• Arranging fire pumps so that all pumps operating in a series can be manually stopped or started from all pump rooms housing the series fire pumps.• Displaying the suction and discharge pressures from all pumps operating in series in all pump rooms housing the series fire pumps. • The presence of alarms and signals that sound in other pump rooms for all pumps that are part of the series fire pump unit.• Standard compliant interconnect control wiring between the controllers in different pump rooms• A standard compliant pump room communication system.The readiness and reliability of fire protection systems is critical — particularly in high-rise buildings. The updated criteria for fire pumps arranged in series in the latest edition of NFPA 20 helps ensure these types of pump arrangements are installed correctly so they can communicate as intended — and ultimately avoid potential pump failure or damage.Brian Buscher is a global marketing manager for Xylem’s A-C Fire brand, with expertise in centrifugal pump systems for fire suppression in industrial and commercial facilities. He is a principal member on the NFPA 20 Technical Committee on Fire Pumps. Any comments/opinions made are the author’s own and not those of NFPA.