NFPA 20: Changes to the fire pump standard
Regardless of whether the 2016 edition of NFPA 20 will be applicable to the next nonresidential building project, fire protection engineers need to be aware of recent changes to the standard.
- Know the basics of NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection.
- Understand the changes to the 2016 edition of NFPA 20, including all types of fire pumps and the electrical aspects of NFPA 20.
The 2016 edition of 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 as well as the introduction of a multistage, multiport pump. The overall intent is to standardize fire pump design in high-rise structures to ensure an appropriate level of reliability.
The fire pump is a vital part of a building’s fire suppression system. It is responsible for pulling water from some dedicated source—either an underground public water supply main or a water source, such as a well, water-storage tank, lake, or other body of water—into the building in the event of a fire. A fire pump becomes necessary when the water supply is insufficient to provide the proper water pressure for the fire suppression system to function as designed.
Fire pumps serve as critical and essential components of many water-based fire protection systems, such as sprinkler, standpipe, foam, water-spray, and water-mist systems for commercial and industrial applications. Where determined to be necessary, a fire pump installation provides for the required water pressure that is vital for the fire protection system performance.
It is imperative that pump selection be made carefully, so that it will work properly when called upon for service. In addition to being sized properly, the pump must be installed correctly and maintained regularly as required by NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. The standard pump used for fire protection service is normally a centrifugal horizontal or vertical split-case, single-stage, or multistage pump. However, the pump can also be a positive-displacement pump or vertical-shaft turbine pump.
Types of fire pumps
Centrifugal pumps are the most popular fire pumps and are classified as nonpositive-displacement pumps because they do not pump a definite amount of water with each revolution. Rather, this type of pump imparts velocity to the water and converts it to pressure within the pump itself. Nearly all modern fire apparatus use a centrifugal pump as the main fire pump. Centrifugal pumps can be mounted vertically or horizontally and are commonly driven by diesel engines or electric motors. Horizontal pumps are used in positive-pressure situations, such as the water supply coming from an elevated storage tank or the city water main. On the other hand, vertical pumps are used where there is a lack of positive pressure. This commonly occurs with reservoirs, ponds, underground storage tanks, and well systems.
Inline pumps (space savers) are installed within and supported by the suction and discharge piping. These pumps work well in compact spaces due to a reduced footprint. They are designed for easy maintenance; the motor and pump rotating assembly pulls out easily from the top without removing the pump casing from the piping.
Positive-displacement pumps move water by trapping a certain amount of the water before pushing it out through the discharge line. These pumps have an expanding cavity on the suction side and a decreasing cavity on the discharge side, allowing liquid to flow into the pump as the cavity on the suction side expands and then flow out of the discharge as the cavity collapses. These pumps fall under two major categories: piston and rotary gear, with the latter being most commonly used in fire pump applications. Positive-displacement pumps are still a necessary part of the overall pumping system on modern fire apparatus because, unlike centrifugal pumps, they can pump air. Due to this feature, positive-displacement pumps are typically installed in special-hazard fire protection systems, such as foam and water-mist systems.
Vertical-shaft turbine pumps are centrifugal pumps with one or more impellers mounted on a vertical shaft. They are unique in that the impellers are intended to be submerged in the water source. They are used for installations where the water source is below the pump impellers. These pumps have a bowl assembly, which often contains several impellers on a vertical shaft, with the discharge of each impeller directly feeding the suction of the next impeller. Impellers are mounted on a column assembly built to a specified length. A discharge head assembly holds the motor or right-angle gear drive. In a fire pump room, the discharge head assembly of a typical vertical turbine pump is the only visible part of the pump.
Multistage, multiport (multiple-outlet) pumps comprise several pump assemblies in series, with outlet ports between impellers driven by a single motor. The available pressure increases with each impeller stage. These pumps are predominantly used to serve multiple zones with different pressure requirements in high-rise buildings. A single fire pump controller can be provided with multiple pressure-sensing devices so that each discharge port may be equipped with its own sensing line. Each discharge port requires its own pressure-maintenance pump, or jockey pump, and jockey pump controller.
Multistage multiport pumps
Multistage multiport pumps were introduced into NFPA 20 in the 2016 edition as an alternative to arranging separate fire pumps in series to serve high-rise buildings having system zones with widely different pressure requirements. Multistage multiport pumps operate similarly to separate pumps arranged in series, except that their stages are all driven by a single motor and there are no shutoff valves between successive stages (18.104.22.168, 4.8.2).
Multistage multiport fire pumps must have a bypass installed between the inlet and the first outlet port, and between successive outlet ports, whenever such a bypass can provide pressure-of-material value without the assistance of the bypassed impeller (22.214.171.124). This requirement echoes a similar requirement for individual fire pumps or fire pumps arranged in series. It is intended to allow the water supply to still provide flow to the fire protection system at a reduced pressure, if an impeller should fail.
The automatic circulation relief valve for a multistage multiport fire pump must be installed between the outlet of the last stage and its discharge check valve and set below the churn pressure, or shutoff pressure, of the first port (126.96.36.199.1). The purpose of this requirement is to ensure that a limited flow of cooling water will flow through the latter stages of the pump, exiting via the circulation relief valve to maintain cooling of the impellers.
Each discharge port is required to have its own individual pressure-sensing line connected to the fire pump controller and to the pressure-maintenance pump controller (188.8.131.52).
Series fire pump unit arrangements
Subsection 4.20.2, Series Fire Pump Unit Arrangements, was substantially restructured in the 2016 edition with a number of new requirements. Series fire pump units are all fire pump units that operate in a series arrangement, where the first pump takes its suction from a water supply and each successive pump takes its suction from the outlet of the previous pump. Pumps that fill tanks are not considered to be in series with the pumps supplied by those tanks.
Series fire pump units must be located in the same room, unless the installation meets a specific set of requirements. There are considerable benefits to locating series pumps in the same room:
- Locating pumps close to one another, and at the same elevation, will maintain higher suction pressures at downstream pumps when an upstream pump is out of service. This will reduce the likelihood of cavitation, and consequent impeller damage, should an upstream pump fail.
- Colocation of series fire pumps allows straightforward assessment of pump status and operation during a fire event.
To install a series arrangement of fire pumps with units in more than one room, the following requirements must be met (184.108.40.206):
- Each pump can be manually stopped or started from any room where any pump in the series arrangement is installed.
- The suction and discharge pressures for each pump operating in series are displayed in all of the pump rooms.
- All alarms and signals for all pumps must be annunciated in each pump room. Requirements for alarms and signals are listed in 220.127.116.11 and 18.104.22.168.
- The interconnect control wiring between the controllers in different pump rooms must meet specific requirements listed in 22.214.171.124 and 126.96.36.199.
A communication system is provided among the pump rooms, complying with specific requirements shown in 188.8.131.52 and 184.108.40.206. In particular, that system must meet survivability requirements of NFPA 72: National Fire Alarm and Signaling Code. Series fire pump unit arrangements may include no more than three pumps (220.127.116.11), of which no more than two can be variable-speed pumps (18.104.22.168).
Chapter 5 covers requirements for fire pumps installed in high-rise buildings. Subsection 5.5 in the 2016 edition calls for a reliable emergency source of power, or a backup fire pump, where electric fire pumps are used in those buildings. The 2013 edition required an emergency source as well, but that requirement applied only to buildings whose height was beyond the capability of the fire department pumping apparatus. This change was instituted to harmonize the requirements of NFPA 20 with those of NFPA 101: Life Safety Code and model building codes. Those codes have standby-power requirements for buildings that are considered high-rise, which include connecting the electric motor-driven fire pump.
The overcurrent protection device (OCPD) in the normal power supply to the fire pump controller is specifically permitted to provide only instantaneous protection for the circuit, without any long-time or short-time overcurrent protection (22.214.171.124.2). This arrangement is permitted because of the special requirements for normal-power OCPDs for fire pump circuits: They must be able to carry the locked-rotor current of the fire pump motors plus the full-load current of other connected loads—roughly six times the running current—indefinitely. The overload protection provided in the fire pump controller is the only overload protection permitted in the normal supply to the fire pump, and is the only device permitted to open the motor circuit under locked-rotor conditions (10.4.4), so the circuit’s OCPD provides protection only for short-circuit or ground faults.
The OCPD in the alternate-source circuit to the fire pump controller must be supervised and remotely monitored (126.96.36.199). This requirement is new to the 2016 edition. The intent is to ensure that alternate power will not be unexpectedly unavailable should normal power fail, due to the incorrect position of the circuit breaker. Subsection 10.4.7, Signal Devices on Controller, does not require any monitoring of the integrity of the alternate source. Because the typical installation employs a diesel generator that does not run until normal power fails to one of its loads, the fire pump controller has no way to determine whether the upstream breaker is open or closed during normal operation.
There is no corresponding requirement for the normal-power circuit breaker. The source serving the controller is remotely monitored (10.4.7.2.4.1), and the controller is required to start and transfer to the alternate source whenever normal power becomes unavailable. Tripping of the normal-power circuit breaker will prompt the controller to start the generators and transfer to the alternate source, and that condition will be annunciated remotely.
OCPDs in the alternate-source circuit are required to be selectively coordinated with upstream overcurrent devices (188.8.131.52). The 2016 edition specifically states that the fire pump breaker need not be coordinated with a single upstream device that serves no other loads (184.108.40.206). This exemption for series circuit breakers echoes similar exemptions in the NFPA 70: National Electrical Code (NEC) regarding selective coordination of standby-system OCPDs.
Previous versions of NFPA 20 prohibited using either the fire pump controller or transfer switch as a junction box for serving other equipment, such as pressure-maintenance controllers or pumps (9.7.7(6)). The 2016 edition also prohibits using those devices as junction boxes for wire splices.
2017 NEC requires surge protection either in or at the fire pump controller. This requirement is new to 2017 NEC. The 2016 edition of NFPA 20, like previous versions, requires a surge arrestor at the controller but describes exceptions for controllers either rated less than 600 V or rated to withstand 10 kV without damage in accordance with specific standards (10.4.1). The 2017 NEC provides no such exceptions and appears to generally cover all fire pump installations without regard to their characteristics.
Provisions to interlock or remotely shut down fire pump controllers may not be installed, except with the approval of the authority having jurisdiction (10.3.4.5.3). This prohibition was added to the 2016 edition to clarify the intent of the code. Capability for remote shutdown is prohibited because fire events may not always be discernable from remote locations. Interlocks are prohibited to avoid failure of the pump to start due to interlock failure or inadvertent activation.
The controller for a multistage multiport fire pump must have a dedicated pressure sensor, in the form of either a switch or electronic sensor, for each of the fire pump’s discharge ports (10.5.1.1.2). It also must have a dedicated pressure recorder for each stage of the pump (10.5.1.1.3). Separate sensors and recorders are required because the system may see a pressure drop on only one of its ports during a fire event. These provisions were added to support the addition of multistage multiport pumps to the code.
The 2016 edition contains new monitoring and annunciation requirements for systems that use electronic pressure systems to automatically control fire pump operation (10.5.2.1.3). These sensors must be monitored during automatic testing, and certain test conditions must be annunciated. Electronic pressure sensors may exhibit temperature sensitivity, and their zero and span may drift over time. When an automatic start is initiated by operation of the solenoid drain valve, the actual sensed pressure will be near zero; if a pressure sensor reads more than 10 psi during an automatic start initiated by the solenoid drain, the controller must actuate a visible and audible alarm. The controller must also actuate a signal whenever the transducer reads below 10% of its rated span, below its rated zero-pressure output, or more than 10% above its rated full-scale output.
Tom Divine is a senior electrical engineer and project manager at Smith Seckman Reid Inc. He is a member of the Consulting-Specifying Engineer editorial advisory board. Wil Semien is a plumbing/medical gas/fire protection engineering designer at Smith Seckman Reid Inc.
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