NFPA 20: Changes to the standard on fire pumps
Regardless of whether the 2013 edition of NFPA 20 will be applicable to your next project, fire protection engineers need to be aware of the changes to the standard.
By Milosh Puchovsky, PE, FSFPE, Worcester Polytechnic Institute, Worcester, Mass
Fire pumps serve as critical and essential components of many water-based fire protection systems such as sprinkler, standpipe, foam water, water spray, and water mist for a wide range of commercial and industrial applications. Where determined to be necessary through hydraulic analysis or other purposes, a fire pump installation provides for the required water flow and pressure for the fire protection system. Without a properly designed and installed fire pump, the fire protection system cannot be expected to meet its objectives.
This article reports on certain key changes to the 2013 edition of NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection, which was released in the summer of 2012. It is assumed that the reader has a basic understanding of the use of fire pumps, fire pump installation requirements, and the role of NFPA in establishing these requirements.
Overall, NFPA 20 received 264 proposals for revision, 135 official follow-up comments, and 2 successful floor actions at NFPA’s 2012 Technical Reporting Session in Las Vegas.
Fire pumps, whether centrifugal or positive displacement, are specifically listed as such, and the standard was revised to clarify that only fire pumps can be used for fire protection. The previous edition addressed “other pumps” with different design features than those addressed by the standard, and permitted such other pumps to be installed where listed by a testing laboratory. However, because all electric motor driven pumps are listed as electrical devices, some interpreted this provision as allowing the use of any electric motor driven pump as a fire pump. This was not the intent and the language was revised to better clarify this.
To facilitate the review and approval by the authority having jurisdiction (AHJ) and other stakeholders involved with the fire pump installation, new provisions concerning design details and drawings have been added. The standard will now require that associated plans be drawn to an indicated scale on sheets of uniform size. Additionally, plans are now to include specific details about various features of the overall installation such as those pertaining to the pump make, model and size, water supply, suction piping, pump driver, controller, and pressure maintenance pump.
Where a water flow test is used to determine the adequacy of the water supply connected to the fire pump, NFPA 20 will now require that test be completed not more than 12 months prior to the submission of working plans, unless otherwise permitted by the AHJ. There was concern that in some instances, old test data that did not properly reflect the current condition of the water supply was being used as a design basis for fire pump selection. In such situations, where the water supply is actually less than that indicated by the older test data, acceptance testing is likely to indicate that pump discharge pressures are less than calculated and not sufficient for the overall system demand. Water supply evaluation and testing is complex and requires an understanding of the water system arrangement and operation, and should only be done by competent personnel.
Fire pump rooms
Pump rooms and separate pump houses containing fire pump equipment require special protection as outlined in tabular form in NFPA 20. One of the entries in the associated table refers to unsprinklered pump rooms and pump houses. Some readers of NFPA 20 incorrectly interpreted this heading to imply that NFPA 20 permitted sprinklers to be omitted from such spaces in those buildings where a sprinkler system is required or being considered. Advisory language was added to explicitly state that the purpose for the “Not Sprinklered” heading in the table is to identify the type of fire protection for the fire pump in unsprinklered buildings—that is, the pump room needs to be separated from the remainder of the building by 2-hour-rated construction, or the pump house needs to be located at least 50 ft from the building served by the pump house. The purpose of the heading is not to provide an exception for omitting sprinklers in the fire pump room in fully sprinklered buildings.
NFPA 20 provides for protection of the fire pump equipment as well as for personnel that need to access the fire pump equipment during a fire situation. While NFPA 20 requires that access to the fire pump room be pre-planned with the fire department, it now requires that the location of the fire pump room also be pre-planned. In addition, NFPA 20 requires that an enclosed passageway from an enclosed stairway or exterior exit doorway to the pump room be provided for those pump rooms not directly accessible from the exterior of the building. The previous edition of NFPA 20 mandated that the passageway posses a minimum 2-hour fire-resistance rating.
The 2013 edition has been revised to require that the passageway possess the same fire-resistance rating as that required for the pump room; that is, in fully sprinklered buildings including the pump room only a 1-hour fire resistance rating is required for the passageway. The fire-resistance rating of the passageway to the pump room need not exceed that required for the fire pump room. If the fire pump room and passageway were constructed as a single directly connected area, then the passageway would essentially become a part of the fire pump room and would only be required to be separated with the same fire resistance rating as that required for the fire pump room. Note that additional provisions on this subject pertain to high-rise buildings.
To minimize turbulence at the suction flange, NFPA 20 prescribes the nominal size of the suction pipe based on the capacity of the fire pump. These prescribed pipe sizes are based on a maximum flow velocity of 15 ft/sec at 150% of the pump’s rated capacity. Users of NFPA 20 will note that this provision has been removed from the body of the standard and added as footnote to a table. Some users of the standard were misinterpreting this velocity information as a condition of verification during pump acceptance testing. Rather, the purpose for including this information was to provide some background regarding the origin and development of the prescribed suction pipe sizes.
Unless specific conditions are satisfied, NFPA 20 requires that the suction piping be arranged to ensure that a negative pressure not occur at the pump suction flange. Centrifugal fire pumps are not intended to lift or pull water toward their suction flange. The provision that suction pressures not drop below 0 psi at the suction flange applies to installations consisting of a single pump unit and to those consisting of multiple fire pump units intended to operate together. A revision to this provision clarified that for a multiple pump installation, only those pumps designed to operate simultaneously are to be considered when evaluating suction pressure conditions. Some users of NFPA 20 were misinterpreting this requirement to include redundant pumps, or those pumps that would operate only when the primary pump was out of service. This was not the intent of this provision.
An existing exception to the requirement for positive pressure at the suction flange specifically permits a -3 psi suction pressure. This exception applies to a scenario consisting of a fire pump operating at 150% of its rated flow while taking suction from a ground level water storage tank. Annex text addressing this exception was revised to address all types of centrifugal fire pumps, and not just those of the horizontal type. Additional revisions to the annex text indicate that the allowance for the -3 psi suction pressure reading is to be permitted where the pump suction room elevation is at or below the water level in the water storage tank at the end of the required water flow duration. The previous edition referred to the elevation of the pump room floor and the bottom of the tank. The revised text better ensures that no lift or pull occurs between the tank and the suction flange of the fire pump. As currently stated in the annex, the allowance for the -3 psi suction pressure addresses friction loss in the suction piping when the pump is operating at 150% capacity, and the water in the tank is at its lowest level.
Certain devices in the suction piping can cause an undesirable degree of uneven flow and turbulence, and impede pump operation and performance. NFPA 20 currently states that within 50 ft of the pump suction flange, no valve other than a listed outside stem and yoke (OS&Y) valve can be installed in the suction piping. This provision was revised to clarify that no “control” valve other than a listed OS&Y valve is to be installed within 50 ft. The provision was further revised to specifically address backflow devices. These changes provide for better consistency with other provisions of the standard and clarify the intent of the requirement, which is to restrict only the use of butterfly valves, and allow the installation of OS&Y gate valves, check valves, and backflow devices in the suction piping. Note, however, that the installation of check valves and backflow devices in the suction piping is only permitted where such devices are required by other standards or by the AHJ. Where a check valve or backflow prevention device is required upstream of the fire pump suction, NFPA requires the device to be a minimum of 10 pipe diameters upstream of the pump suction flange.
Fittings such as elbows, tees, and crosses in the suction piping can cause an imbalanced flow of water entering the pump. The imbalance occurs where the fitting changes the plane of the flow relative to the plane of flow through the fire pump. This imbalanced flow will degrade pump performance and useful life. NFPA 20 places limitations on the location and arrangement of such fittings in the suction piping. Such fittings are not to be installed within 10 pipe diameters of the suction flange. A current exception to this provision allows elbows with their centerline plane perpendicular to a horizontal split-case pump shaft to be permitted at any location in the pump suction intake. Such an elbow arrangement does not produce detrimental flow conditions. For the next edition, this exception was expanded to include tees.
Vortex or anti-vortex
Where a fire pump takes its suction from the bottom of a water storage tank, NFPA 20 requires a certain arrangement for the discharge from the tank. As water flows from the tank outlet, a vortex tends to form, introducing air into the suction piping and increasing the occurrence of turbulent flow. A similar phenomenon appears when water drains from a sink or tub. As previously noted, turbulent and imbalanced flow into the pump suction is to be avoided.
To prevent this phenomenon, NFPA 20 requires the use of a device that prevents the formation of a vortex. This device is often erroneously referred to as a vortex plate, but the terminology in NFPA 20 has been revised to better correlate with NFPA 22, Standard for Water Tanks for Private Fire Protection, and to clarify that the device is actually an “anti-vortex” plate used to prevent the formation of a vortex. In addition, reference to the Hydraulic Institute’s “Standards for Centrifugal, Rotary, and Reciprocating Pumps” was added to the annex text for additional information on the subject.
Low-suction throttling devices
Since the 2003 edition, NFPA 20 has permitted the use of low-suction throttling valves where the AHJ requires positive pressure to be maintained on the suction piping. The purpose of such valves is to help ensure that the pressure in the suction piping does not drop to a predetermined critical level due to the condition of the available water supply. For instance, where a municipal water main serves as the water supply for the fire protection system, the main might not be capable of supplying as much water as the fire pump is capable of drawing, especially when the pump is operating near its overload condition. The resulting pressure drop in the municipal main can cause undesirable conditions such as groundwater or backflow contamination, or in extreme cases a collapse of the main.
Where a low suction throttling valve is required by the AHJ, NFPA 20 requires such throttling valves to be installed in the discharge piping between the pump and the discharge check valve. A sensing line connected to the suction piping controls the position of the throttling valve. When the suction pressure drops to a preset throttling pressure (typically 20 psi), the valve begins to close thereby limiting flow and maintaining the suction pressure to the preset level.
When water flows through the throttling valve, friction loss occurs and needs to be accounted for in the system design. The friction loss associated with these devices can be significant. For example, flow through an 8-in. device could cause as much as a 7 psi pressure drop. Although the current edition included advisory text addressing this situation, the 2013 edition will mandate that the friction loss through a low suction-throttling valve in the fully open position be taken into account in the design of the fire protection system.
Supervising test header valves
NFPA 20 requires that test outlet control valves be supervised in the closed position. As previously worded, the provision could have been mistakenly interpreted to mean that valves on the individual hose connection outlets attached to the test header manifold be supervised. This was not the intent of the standard. The provision has been clarified to indicate that the control valves located in the pipeline between the discharge piping and the hose valve test header manifold are required to be supervised in the closed position; the exterior valve on each outlet of the test header is not required to be supervised.
Protection of piping against damage due to movement
The previous provision requiring a clearance of not less than 1 in. be provided around pipes that pass through walls or floors underwent significant revision. The scope of the provision was narrowed to include only walls, ceilings, and floors of the fire pump room enclosure. The use of other clearances, pipe sleeves and flexible couplings was addressed, and better correlation with the requirements of NFPA 13, Standard for the Installation of Sprinkler Systems, on the subject was provided.
The term “pressure relief valve” is typically applied to a large valve sized to discharge a large flow of water from the fire pump discharge. The use of this valve is limited to specific applications. The term “circulation relief valve” refers to a small pressure relief valve that is intended to discharge a small flow of water for cooling when water is not being discharged downstream of the fire pump. A circulation relief valve is required between the fire pump discharge and the discharge check valve on electric motor and radiator cooled diesel engine centrifugal fire pumps. An additional circulation relief valve is required downstream of a pressure relief valve that is piped back to suction. An additional circulation relief valve is also needed when a meter test loop is piped back to the fire pump suction.
The provisions concerning pressure relief valves were rearranged to more clearly indicate that pressure relief valves are permitted only when the following “abnormal” pump operating conditions cause system components to be subjected to pressures in excess of their pressure rating: (1) diesel engine pump drive operating at 110% of rated speed, and (2) electric variable speed pressure-limiting controller operating in across the line mode (at rated speed).
NFPA 20 allows for discharge from the pressure relief valve to be piped back to the suction piping. A new provision for the 2013 edition pertains to pumps driven by a diesel engine that incorporates heat exchanger cooling for the engine. For such arrangements, a high cooling water temperature signal at 104 F from the engine inlet of the heat exchanger water supply is to be sent to the fire pump controller. Upon receipt of this signal, the controller is to stop the engine provided there are no active emergency signals calling for fire pump operation.
The recirculation of water from the pump discharge back to the pump suction piping can create a concern because the recirculated water is used to cool not just the engine, but also the engine intake air temperature. Cooling of the engine intake temperature is critical in satisfying engine emission requirements of the U.S. Environmental Protection Agency. Temperatures in the range of 150 F have been observed. While there might be sufficient water flow at these elevated temperatures to sufficiently cool the engine, air inlet temperatures cannot be sufficiently cooled and can cause the engine to operate outside the range necessary for EPA compliance. Although the pressure relief valve is to be set to open only under conditions of over-pressurization and a circulation relief valve is also to be installed to help maintain water temperatures, this additional precaution was developed to ensure compliance with the broader concerns pertaining to fire pump installations.
Series fire pump unit arrangement: The change that wasn’t
For the 2010 edition, the concept of the series fire pump unit was introduced, and describes an arrangement of fire pump units intended to operate in unison such that the first pump takes suction directly from a water supply and each sequential pump takes suction from the preceding pump. Such series units are most common in high-rise buildings and other large-scale buildings and structures. For the past two revision cycles including that for the 2013 edition, the Technical Committee on Fire Pumps expended significant energy in deliberating the provisions for the arrangement of series fire pump units.
The central issue pertains to the location of the fire pump units. Its has been proposed for the past two cycles that all pumps comprising the series fire pump unit arrangement be located in the same fire pump room. For the 2013 edition, an exception was developed that would allow the fire pump units to be located in separate rooms under certain conditions. While this language made it through the Fire Pump Committee deliberations, it was returned on the floor of NFPA’s Association Technical Meeting this past June. Although the proposed change will not go into effect, the subject is likely to be brought up again during the next revision cycle. Debate regarding the difficulty with supervising the operation of multiple fire pump units under emergency conditions, facilitating appropriate testing functions, and ensuring overall systems reliability will continue. Additionally, it’s worth noting that while NFPA 20 will continue to permit the vertical staging of fire pump units, some jurisdictions do not allow such an arrangement.
Test headers and meters
Where a fire pump test header is installed, NFPA 20 requires that it be installed on an exterior wall or in another location outside the pump room that allows for water discharge during testing. An outdoor arrangement facilitates discharge of water flow to a safe location and minimizes the impact of inadvertent water discharge on the fire pump, controllers, motor, diesel engine, etc. New annex text was added to address conditions under which the test header could be considered for location within the building. In situations where damage from theft or vandalism is of concern, the test header hose valves may be located within the building but outside of the fire pump room, if in the judgment of the AHJ, the test flows can be safely directed outside the building without undue risk of water spray onto the fire pump equipment.
NFPA 20 has permitted the use of a flow meter as a water flow test device for quite some time. Where installed, NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, requires that the flow meter be tested and recalibrated every three years. However, NFPA 20 contained no provisions facilitating the calibration or recalibration of the flow meter. The 2013 edition will now require that where a metering device is installed in a looped arrangement for fire pump flow testing, an alternate means of measuring flow also be provided. The alternate means is to be located downstream of and in series with the flow meter, and is to function for the range of flows necessary to conduct full flow tests of the fire pump. Furthermore, the standard will now state that an acceptable alternate means of measuring flow is an appropriately sized test header. Unless an arrangement as described by the above new provisions was provided, calibration of the flow meter required physical removal of the device and testing in an arrangement that might not reflect the actual pump and piping installation. This practice can be cumbersome and costly over the long term. Additionally, piping arrangements and variations of the test arrangement might not match those of the actual pump installation, and can call into question the results of the recalibration.
The previous edition of NFPA 20 required that where the test header is located outside or at a distance from the pump and there is a danger of freezing, a listed indicating butterfly or gate valve and a drain valve or ball drip be located in the pipe line to the test header. This provision was revised to require a butterfly or gate valve and a drain valve or ball drip in all cases. Without the valve, water would be under pressure to the point of the test header, which is cause for concern. Water could be discharged from the fire protection system through the test header rather easily for non-fire protection use. Another concern is for the safety of the personnel conducting the pump test. The connection of hoses to the test header is more safely completed with no water pressure at the test header. The ball drip and drain valve relieves pressure and water from the piping when testing is complete.
NFPA 20 currently states that where a backflow prevention device is required in connection with the pump, special consideration is to be given to the increased pressure loss resulting from the installation of the backflow prevention device. As such NFPA 20 requires that a suction pressure of at least 0 psi be recorded for the installation when the fire pump is operating at 150% of its rated capacity. This requirement could have been interpreted to mean that the suction pressure is to be recorded at the backflow device rather than at the pump suction flange. The next edition clarifies that the pressure reading is to be taken at the fire pump suction.
The requirements regarding earthquake protection have been clarified to indicate that they apply only where local codes specifically require fire protection systems to be protected from damage subject to earthquakes. Additionally, the previous provisions pertaining to pump components being installed so they are capable of resisting lateral movement from horizontal forces equal to one-half the weight of the equipment have been removed. NFPA 20 now requires horizontal seismic loads to be based on NFPA 13; SEI/ASCE7; or local, state, or international sources acceptable to the AHJ.
These changes provide for more consistency with current approaches used in protecting buildings and associated mechanical systems from the forces caused by seismic events. The concept of using half of the equipment weight is not prudent in all cases. The user of NFPA 20 needs to be aware that the resulting horizontal loads will vary based on the project site location. While NFPA 13 offers a simplified approach to determining the loads, and SEI/ASCE7 contains a more comprehensive method, NFPA 20 does not mandate the use of these reference standards and allows the AHJ to make the final determination.
Packaged fire pump assemblies
Packaged fire pump assemblies are defined by NFPA 20 as fire pump unit components assembled at a packaging facility and shipped as a unit to the installation site. The components required to be listed in a pre-assembled package include the pump, driver, controller, and other accessories identified by the packager that are assembled onto a base with or without an enclosure. The provisions for packaged assemblies have been expanded. The pump unit components are to be assembled and affixed onto a steel framing structure. Welders assembling the packaged unit are to be qualified in accordance with Section 9 of the ASME Boiler and Pressure Vessel Code, or with the American Welding Society AWS D1.1. The entire assembly must be listed for fire pump service and engineered and designed by a system designer as described in NFPA 20. Lastly, all plans and data sheets are to be submitted and reviewed by the AHJ with copies of the stamped approved submittals maintained for record keeping.
These changes were instituted to provide more control over who has responsibility for ensuring that the packaged pump unit is manufactured, installed, and operates as intended. While the fire pump manufacturer was typically the entity called upon to troubleshoot any issues with the installation, the pump manufacturer was not necessarily the party that assembled the packaged fire pump assembly.
In some jurisdictions, a direct connection between the fire pump and the water source, such as from a municipal water main, is not permitted. In other cases the municipal or other water source is not capable of providing the maximum flow rate required by the fire protection system, or possesses a wide fluctuation in flow conditions. In both situations, the use of a break tank, which interrupts or breaks the connection to the water source, provides a potential design option. A break tank is a water tank providing suction to a fire pump, but the tank’s capacity or size is less than that required by the fire protection systems served; that is, the tank cannot hold the amount of water necessary for the overall duration of fire protection system operation.
Break tanks are most commonly used (1) as a means of backflow prevention between the water supply source and the fire pump suction pipe, (2) to eliminate fluctuations in the water supply source pressure, (3) to provide a stable and relatively constant suction pressure at the fire pump, and/or (4) to provide water storage to augment a water source that cannot provide the maximum flow rate required by the fire protection system.
NFPA 20 requires that the break tanks be sized so that the water stored in the break tank added to the automatic refill capability must supply the maximum system demand flow rate and duration. The tank must also be sized for a minimum duration of 15 minutes with the fire pump operating at 150% of its rated capacity. Additionally, NFPA 20 includes provisions regarding tank refilling and requires that the refill mechanism be listed and arranged for automatic operation. Specific refilling provisions such as those pertaining to refilling lines, bypass lines, liquid level signals, etc., are based on the overall size of the tank. If the tank is sized so that its capacity is less than the maximum system demand for 30 minutes, one set of provisions applies. If the tank is sized so that its capacity provides at least 30 minutes of the maximum system demand, another set of provisions applies. The paragraphs addressing break tanks were revised and rearranged to clarify the applicable provisions based on the tank size.
NFPA provides additional guidance to facilitate preplanning activities with the fire department on locating and providing access to fire pump equipment in high-rise buildings. As noted in the new annex text, the location of a pump room in a high-rise building requires appropriate consideration. During a fire situation, personnel are typically dispatched to the pump room to monitor or control the operation of the pump.
The most effective way of providing protection for these responding personnel is to make the pump room directly accessible from the exterior of the building. However, this arrangement is not always possible or practical for high-rise buildings. In numerous cases, pump rooms in high-rise buildings need to be located a number of floors above grade or at a location below grade.
When the pump room is not at grade level, NFPA 20 requires protected passageways between the stairs and the fire pump room. The passageway must have the same fire resistance rating as that required for the exit stairwells providing access to the pump room. Many building and life safety regulations do not permit the pump room to open directly onto an enclosed exit stair as the pump room is not a normally occupied space. However, the passageway between the stairwell providing access to the pump room and the pump room on upper or lower floors needs to be as short as possible with as few openings to other building areas as possible. This provides for improved protection of responding personnel traveling to and from the pump room during a fire situation.
Pump rooms also are to be located and arranged so that water discharge from pump equipment, such as from packing glands, and discharge and relief valves is safely disposed of.
Very tall buildings
The concept of very tall buildings was introduced to the 2013 edition as part of chapter 5. High-rise buildings are defined as those with a floor on an occupiable story more than 75 ft above the lowest level of fire department vehicle access. Previous provisions of NFPA 20 largely placed such buildings in the same category regardless of whether the building possessed a height of 200 ft or 2000 ft. However, some buildings are so tall that it is not possible for the pumping apparatus of the responding fire department to overcome the associated elevation and friction losses necessary to meet the fire protection system flow and pressure demands at the highest floors. While previous editions of NFPA 20 referred to structures or zones beyond the pumping capability of the fire department apparatus in certain cases, the 2013 edition makes the requirements for such “very tall buildings” more explicit. However, the reader should be aware that some provisions for such situations are also located chapter 9, which addresses power supplies for electric motor driven fire pump units.
For “very tall buildings,” the fire pump installation needs to be provided with additional protection features and redundancies as noted below. Rather than tie the new provisions for very tall buildings to a specific building height, a performance-based requirement associated with the pumping capabilities of the responding fire department was put forth. Fire departments purchase different apparatus with different pumping capabilities, so a criterion based solely on a maximum building height would be rather limited. The design team will now need to specifically confirm the pumping capabilities of the responding fire department for each individual project. Additional provisions pertaining to redundant water tanks and fire pumps have also been added for very tall buildings.
Redundant water tanks for very tall buildings
Where the primary water supply source is a tank, two or more tanks are required. A single water tank capable of being divided into two compartments will be permitted provided that each compartment can function as an individual tank. The total volume of all tanks or compartments must be sufficient for the full fire protection demand of the associated systems. Each individual tank or compartment must be sized so that at least 50% of the fire protection demand is stored with any one compartment or tank out of service. Note that this provision does not require each individual tank or compartment to be capable of providing the entire system demand. However, each tank and/or tank compartment must have an automatic refill that can provide the full system demand. While the provision for redundant tanks or compartments was introduced for the 2010 edition, it was formalized for very tall buildings for the 2013 edition.
Fire pump redundancy for very tall buildings
Fire pumps serving zones that are partially or wholly beyond the pumping capability of the fire department apparatus must be provided with either a fully independent and automatic backup fire pump unit or units arranged so that all zones can be maintained in full service with any one pump out of service. Another option is to provide for an auxiliary means of providing the full fire protection demand that is acceptable to the AHJ. This second options allows for negotiation with the AHJ in providing the redundant fire pump capabilities. Properly designed gravity feed standpipe systems may be an option for meeting this requirement. Keep in mind that there might be more than one AHJ on a particular design project.
Acceptance testing: Flushing
The suction piping supplying a fire pump needs to be adequately flushed to ensure that stones, silt, and other debris will not enter the pump or the fire protection system and cause impairment. The previous edition of the standard included two tables that specified flushing rates for stationary and positive displacement pumps. For the 2013 edition the tables were combined, apply to all suction piping, and are based on the nominal size of the suction pipe. The flushing rates for the smaller sized pipes were also revised to reflect a water flow velocity of about 15 ft/sec.
Where the maximum flushing flow rates specified cannot be achieved, the standard will permit flushing flow rates in excess of 100% of the rated flow of the connected fire pump, or the maximum flow demand of the fire protection systems, whichever is greater. New language indicates that this reduced flushing flow capacity constitutes an acceptable test, provided that the flow rate exceeds the fire protection system design flow rate.
Furthermore, annex language has been added indicating that if the flow rates as specified in the standard cannot be achieved with the available water supply, a supplemental source such as a fire department pumper might be necessary. The standard will now also include language indicating that the flushing procedure is to be performed, witnessed, and signed off on before connection to the fire pump is undertaken.
Acceptance testing: Field test scheduling
Coordination with the AHJ with regard to the date, time, and location of the field acceptance test will now be specifically required. The previous edition of the standard required only that the AHJ be notified as to the time and place of the test. Annex language also adds the insurance company representative to the list of invitees who should attend the acceptance test. New provisions concerning system demand and pump performance curves, test duration, and record retention as part of acceptance testing were also added. A related provision concerning acceptance testing for replaced components also was introduced.
Acceptance testing: System demand and performance curves
A new provision was added requiring that during acceptance testing, the actual unadjusted fire pump discharge flows and pressures meet or exceed the fire protection system demand. This requirement was added to ensure that the fire pump installation meets both the manufacturer’s certified pump test characteristic curve, often referred to as the shop curve, and the overall fire protection system demand. Situations can arise where an installed pump meets the shop curve but cannot provide the necessary fire protection flow rate and pressure during acceptance testing. This can result from not properly accounting for (1) the lift on a vertical turbine fire pump installation, (2) the friction and elevation losses between the water supply and fire pump suction flange, (3) friction losses associated with flow meters, backflow preventers, and other devices, (4) fluctuations in operating conditions in the water supply, and/or (5) fully or partially closed valves or other obstructions in the water supply piping. Other causes include improperly conducted or analyzed water flow tests, and not verifying pipe sizes in the water supply.
A similar requirement was also added clarifying that the installed fire pump must meet or exceed the shop curve when operating at rated speed under the required testing flow rates, which are typically the minimum (no-flow or churn), rated, and peak (overload) conditions. Another revision regarding the shop curve specifies that all field test results concerning installation acceptance be compared to the shop curve as developed by the fire pump manufacturer.
Where variable speed pressure limiting control is employed, in addition to the three conditions at the rated pump operating speed as noted above, the fire pump will also need to be tested at no-flow, 25%, 50%, 75%, 100%, 125%, and 150% of rated pump capacity in the variable speed mode. These additional testing points verify that there are no stability issues for the range of flows, and ensure that the pump operates under the range of pressure and flow conditions anticipated for the installation. Additional language was added requiring that the system be isolated and the pressure relief valve be closed during rated fire pump speed testing so that the fire pump curve can be properly established. The variable speed tests must be conducted with the system open and the relief valve set to its specified value to verify that there is no interaction with the fire protection system throughout the entire range of flow conditions.
Acceptance testing: Test duration
The standard currently requires that the fire pump be in operation for not less than 1 hour total time during the acceptance tests. While this provision was not modified for the 2013 edition, advisory language was added to aid in the interpretation of the requirement. The intent of NFPA 20 is that the fire pump equipment operates for at least 1 hour. That does not mean that water be discharged for the full 1-hour test provided all flow tests can be conducted in less time and efforts are taken to prevent the pump equipment from overheating. A discharge of water downstream of the pump aids in maintaining proper operating temperatures of the equipment. The section on “Relief valves” contains a discussion of pressure relief valves that are required to operate during pump churn and when returning water to the pump suction. The advisory text serves to reduce the amount of water that is needlessly discharged and better aligns with green building design efforts.
New provisions were added regarding record drawings and test reports. The term “record drawing” is now defined in Chapter 3 as a design-, working- or as-built drawing that is submitted as the final record of documentation for the project. New provisions require that one set of record drawings and one copy of the completed test report be provided to the building owner. This language supplements the existing provision that requires one set of instruction manuals for all major components of the fire pump installation also be provided. With regard to the equipment manual, a list of recommended spare parts and lubricants was added to the list of required contents. Advisory language was also developed indicating that it is NFPA 20’s intent that the record drawing, equipment manuals, and completed test report be retained by the building owner for the life of the fire pump system.
NFPA 20 requires that whenever a replacement, change, or modification to critical path components is performed on a fire pump, driver, or controller, a new acceptance test must be conducted by the pump manufacturer, factory authorized representative, or qualified person acceptable to the AHJ. NFPA 20 previously included a table that specified acceptance retest criteria based on the component under consideration, and whether the component was adjusted, repaired, rebuilt, or replaced. This table has been removed from NFPA 20, and reference is now made to NFPA 25, Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, for these provisions.
Limited service controllers
Thermal magnetic breakers are no longer permitted in Limited Service Controllers. This action addressed the primary concern with such devices and avoided an attempt to remove Limited Service Controllers from NFPA 20. Thermal magnetic breakers might not protect the motor from locked rotor condition, and limited data was provided showing a significantly higher failure rate in smaller horsepower motors that are served by Limited Service Controllers.
Positive displacement pumps
Significant changes for positive displacement pumps include the following:
- Adding this definition of “Water Mist Positive Displacement Pumping Unit”: Multiple positive displacement pumps designed to operate in parallel that discharges into a single common water mist distribution system.
- A Water Mist Positive Displacement Pumping Unit must be listed as a unit.
- A single controller is permitted to control a Water Mist Positive Displacement Pumping Unit.
- A Water Mist Positive Displacement Pumping Unit is allowed to serve as a pressure maintenance pump.
- Certified shop test data is required for each individual pump. Certified shop test data is required for a Water Mist Positive Displacement Pumping Unit operating in the variable speed mode, and also for a Water Mist Positive Displacement Pumping Unit with the variable speed mode deactivated. Note: Positive displacement pumps do not follow a smooth output curve, so “certified shop test data” is a more appropriate term than “certified shop test curve.”
- Test requirements specific to a Water Mist Positive Displacement Pumping Unit were added.
While not specifically addressed as part of this article, a number of changes concerning other aspects of fire pump installations were added. Key changes to electric power supplies for motor driven fire pump units include clarification that means of ground fault interruption and arc fault interruption are not to be installed in any fire pump control or power circuit. Other revisions pertain to sizing of overcurrent protection devices and selective coordination requirements. There were also a number of key changes associated with the requirements for controllers and diesel engine drives.
Applying the appropriate provisions
This article highlights some of the key changes for the next edition of NFPA 20. The reader should consult the Document Information Pages pertaining to NFPA 20 on NFPA’s website, and navigate to the Next Edition tab for more detailed information on the changes for the 2013 edition of NFPA 20.
Regardless of whether the 2013 edition of NFPA 20 will be applicable to your next project, you must be aware of these changes and how they might impact your decision making. Equally important is that you properly identify the correct edition of NFPA 20 applicable to your project, and any local amendments that might be in effect. While a fire will not behave differently based on geographic location, the means by which stakeholders address the relevant issues and concerns often does.
Milosh Puchovsky is professor of practice, department of fire protection engineering, at Worcester Polytechnic Institute, and a member NFPA’s Technical Committee on Fire Pumps. He has more than 20 years of experience in the field focusing on regulations and fire protection systems. He is also the former Secretary to NFPA’s Standards Council overseeing the development of all of NFPA’s codes and standards.
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