FEATURE: SUPPRESSION SYSTEMS
The ongoing debate over provisions of NFPA 20.
NFPA Journal®, November/December 2012
By Chad Duffy
A number of important changes were considered for the 2013 edition of NFPA 20, Installation of Stationary Pumps for Fire Protection, but most of the discussion centered around three issues: series fire pump units, modifications to limited service controllers, and water mist positive displacement pumping units. None of these issues were new — they’ve been put before the Technical Committee on Fire Pumps over the last couple of revision cycles — but the committee believed that all of the changes it supported for the 2013 edition would improve the standard and would be approved by voting members at the Association Technical Meeting in June.
NFPA senior fire protection specialist Chad Duffy explains the engineering and safety issues around series fire pumping units.
That didn’t happen, however. Certified Amending Motions (CAMs) were received on series fire pump units and limited service controllers, and the broader NFPA membership opted in favor of the motion for series fire pump units, meaning the changes approved by the committee would not be part of the 2013 edition. The motion related to limited service controllers failed, meaning the proposed changes remained in place and are part of the new edition. New provisions proposed for water mist positive displacement pumping units did not result in any CAMs. What became clear through the 2013 edition process is that series fire pumps are one of the central issues of NFPA 20. While everyone involved in the discussion wants the standard to require systems that are as reliable as possible, not everyone agrees on how that should happen, and series fire pumps are at the center of that debate.
Series fire pump units
The stationary pumps covered by NFPA 20 are essential elements of effective water-based fire protection systems in a variety of occupancy types. Fire pumps are used when a liquid-based fire protection system, such as an automatic sprinkler system using water, requires pressures in excess of those available from a liquid source, most often the public water supply. In this context, the liquid source is typically a water supply but it may also include foam water solution, foam concentrates, or water additives. This higher pressure may be necessary to overcome pressure loss from elevation (as in a high-rise structure) or system demand (as with a large single-story warehouse facility), or a combination of both. When the fire pump controller detects a loss of pressure in the system, it activates the pump, which increases the system pressure. NFPA 20 offers guidance for the installation of pump systems designed to provide the necessary pressure for the system to work properly.
In certain buildings, multiple pumps are needed to maintain that system pressure. Fire pumps operating in series is a common configuration primarily used in high-rise applications, where the first fire pump takes suction directly from a water supply and each subsequent pump takes suction from the preceding pump’s discharge. A 50-story high-rise might have a pump at the base, and another at the 25th floor, to maintain sufficient water pressure throughout the entire structure. A series fire pump unit was first defined in the 2010 edition of NFPA 20 as “all fire pump units that operate in a series arrangement.” For the 2013 edition, the definition was changed to “all fire pump units located within the same building that operate in a series arrangement.”
Among the new requirements proposed was one that called for locating all of the fire pumps in a series arrangement in the same room. The rationale for the change, which was accepted by the technical committee, is that locating the pumps in the same space provides better protection of life and property by removing the possibility of complete or partial loss of the suppression system if the initial fire pump doesn’t start. If the first pump fails, water can simply be run through it to the second pump in the series, and so on; there may not be sufficient pressure at the top of the building, but most of the structure would have enough pressure for the suppression systems to work properly. Proponents of this approach say that if the first pump fails in a conventional system, with a base pump at ground level and a second pump at the 25th floor, the entire sprinkler system or standpipe system could be left inoperable in a fire event; the pressure of the public water supply might be able to supply sprinklers up to several stories, but most of the building would be unprotected.
Another proposed change provided an exception to the same-room requirement for multiple pumps. The exception would have allowed series fire pumps to be located in different rooms if each pump had positive pressure at maximum flow — in other words, if the first pump wasn’t running but there was still sufficient pressure when the water reached the second pump on a higher floor. That pressure would only be provided by the public water supply, however, meaning the second pump would have to be located on a much lower floor than if the first pump were operating. Other exception requirements focused on communications between the pumps, as well as between pump operators (including building maintenance personnel and firefighters) who are required to monitor the pumps in a fire event. Those requirements called for pumps to include interconnected control wiring that was protected from fire and physical damage; for alarms and signals to annunciate in other pump rooms for all pumps in the series; and for a two-way in-building emergency communication system, designed and installed in accordance with NFPA 72®, National Fire Alarm and Signaling Code.
The same-room requirement, as well as the exception, faced opposition from contractors, engineers, enforcers, and insurers. Opponents argued that the premise for the same-room requirement was unfounded — the statistical data did not demonstrate failures of the initial pump to start — that it contradicted design and installation practices that had been used for many years, and that it could drastically impact how these systems would be designed going forward. They also said the proposed exception would limit the elevation of pumps beyond the base pump, and that the costs of the additional communications systems, and the protection of those systems, would be prohibitive. Opponents appeared to be more in favor of a requirement of a backup pump at the initial pump location instead of limiting the location of successive pumps.
Opponents also said that the new provision could impact NFPA 14, Installation of Standpipes and Hose Systems — the CAM was initiated by the Technical Committee on Standpipe Systems — by forcing it to modify what is currently permitted as an acceptable standpipe design and installation practice. They argued that this change would have a cost impact that would affect engineers and contractors who design and install the systems using currently accepted practices.
The objections to the series fire pump units proposal were upheld at the Association Technical Meeting, meaning that the provision was not included in the 2013 edition of NFPA 20. For now, series fire pump fire units can be arranged in various configurations throughout a building, provided there is adequate pressure for the pumps to work and for the sprinkler or standpipe systems to function properly.
Limited service controllers
One of the other new requirements focused on “limited service controllers,” or LSCs. Fire pump controllers contain switches, relays, and other components designed to receive signals from alarm devices, activate fire pumps, and monitor the pumps’ operation. These devices are typically either full service controllers (FSCs) or LSCs. A proposed change to the standard required LSCs to use the same circuit breakers as FSCs to improve their performance. As with series fire pump units, the proposal resulted in much discussion among technical committee members and generated a CAM at the Association Technical Meeting.
A bit of background. FSCs have been around for decades, but were typically expensive and were sometimes viewed as a deterrent to installing fire protection systems in a building, especially in jurisdictions that did not require such systems. LSCs were introduced as stripped-down, more affordable alternatives to FSCs. LSCs could only be used with smaller pumps, the kind often found in modest-sized commercial occupancies. That’s why small businesses were a primary audience for these systems; business owners could find peace-of-mind knowing they were protecting their building, their goods, and their employees.
Recently, though, FSCs have become more affordable and are the most commonly used controllers for use with fire pumps; NFPA 20 requires that LSCs only be used in special situations where acceptable to the authority having jurisdiction. The limitations of LSCs include their lack of an isolation switch; their use of breakers that can fail, disabling the pumps; and the fact that they can only be used with fire pump motors of 30 hp or less.
That’s why the circuit breaker point is just part of a larger discussion, ongoing for several code cycles now, over whether LSCs should be removed from the standard entirely in favor of FSCs. The electrical community, in particular, views LSCs as deficient when compared to FSCs and is primarily concerned about the impact of heat on the devices’ breakers. Other committee members, however, contend there is still a need for LSCs in the fire protection industry, saying that LSCs are still a more affordable option to FSCs — though the savings are often minimal considering the overall cost of a complete pump system — and can help remove a barrier to installing suppression systems in some jurisdictions. In their view, some fire protection is better than none. Contractors argue that LSC failures haven’t been documented to show a need to eliminate them from the standard.
After much discussion during the NFPA 20 cycle, the technical committee decided not to eliminate LSCs from the standard, choosing instead to support the change requiring upgraded circuit breakers, which some members believed could improve the reliability of LSCs.
The change requires LSC manufacturers to install the same breaker used in an FSC. The upgraded breakers have a much quicker trip time and typically will not fail due to overheating; in a fire event, this would give pump operators a chance to reset the breaker and attempt to start the fire pump. A CAM on this requirement was voted down at the Association Technical Meeting, meaning the upgraded circuit breaker requirement is included in the 2013 edition of NFPA 20.
Water mist positive displacement pumping unit
Another important suppression system element that received a lot of attention (but no CAMs) was water mist positive displacement pumping units. Advocates say these systems use less water than other water-based systems and cause less water damage to property when activated. These systems are used in Europe in some hotels and other occupancies, and are used for fire suppression aboard ships. In the United States, water mist systems are typically installed for highly localized applications in small buildings, such as protecting computer server rooms.
As manufacturers of fire protection systems continue to make advancements, they require the standards to recognize designs and installations that will permit the use of new products. With this in mind, the technical committee accepted a new set of criteria for requirements on water mist positive displacement pumping units, an assembly that was previously unrecognized by the standard. This change allows larger water mist systems where multiple positive displacement pumps are needed to meet system demand.
Whereas a standard sprinkler system is designed around the square footage of the floor area for its coverage, water mist systems must be able to fill the entire volume of a given compartment. As a result, the pumps used in mist systems use higher pressures at specific volumes than other pumps, but they can only move a certain volume of water, which is why larger spaces require multiple pumps to meet the larger flow demand. The language for the new requirements refers to “multiple positive displacement pumps designed to operate in parallel that discharge into a single common water mist distribution system.”
The technical committee had only limited experience with the performance and inner workings of these pump units, however, and it formed a task group that was able to witness the application of a water mist system on a fire in a testing laboratory. The test resulted in the new and accepted criteria for the 2013 edition, including the requirement that the entire assembly — pumps, driver, and controller — be treated as a single unit and that the unit be tested and listed by a recognized testing body. As the NFPA 20 annex explains, the term “water mist positive displacement pumping unit” is only intended to apply to water mist systems designed with multiple pumps where a pump operates individually or multiple pumps operate in parallel, based on the demand of the system downstream and the number of nozzles that discharge. The term does not apply to a single pump used to supply water to a mist system.
These new criteria raised concerns for some members of the NFPA 20 committee, however. NFPA 20 has a longstanding requirement of one pump and driver operated by one controller; given the acceptance of new criteria for water mist positive displacement pumping units, this requirement has been revised to allow the controller in these units to run several pumps. Some members feel that there has not been enough experience or testing with the units to provide the data necessary to establish design and installation criteria. They also question why positive displacement pumping units will be permitted to have requirements that they see as less stringent than those currently in the standard, namely the requirement for one pump and driver to be operated by one controller.
There is a lot of discussion going on around mist systems in the sprinkler world, but it’s more related to applications and systems than to pumps. The NFPA 20 Technical Committee on Fire Pumps believes the pump requirements for mist systems are complete, at least for now, but it probably wouldn’t surprise anyone if pumps, as well as an assortment of other topics, need to be addressed in some fashion as part of the 2016 edition of the standard.
Chad Duffy is a senior fire protection specialist at NFPA and staff liaison for NFPA 20.