Designing sprinkler systems for maintainability

Best practices for designing an automatic sprinkler system that can be easily inspected, tested, and maintained.

04/21/2017


This article is peer-reviewed.Learning Objectives

  • Learn about the codes and standards that fire protection engineers should reference when designing fire sprinkler systems.
  • Understand that inspection, testing, and maintenance are key to compliant fire sprinkler systems.

A sprinkler system designed strictly in accordance with the requirements of NFPA 13: Standard for the Installation of Sprinkler Systems does not necessarily lend itself to a simple regimen of inspection, testing, and maintenance. A sprinkler system designer needs to understand the various post-installation inspection, testing, and maintenance procedures required by NFPA 25: Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems to design a system that can be inspected, tested, and maintained efficiently.

NFPA 13 serves as the primary automatic fire sprinkler system design and installation standard in the U.S. It is also adopted and used for fire sprinkler system design in locations outside of the U.S. Once sprinkler systems are installed, the application of effective inspection, testing, and maintenance (ITM) is required to ensure system performance during a fire event. NFPA 25 is the established standard for sprinkler system ITM criteria. An NFPA 13-compliant sprinkler system will include the minimum system features required to complete NFPA 25 ITM activities. However, even an NFPA 13 code-compliant system does not automatically lend itself to applying the most efficient ITM.

Figure 1: This photo shows a 4-in. drain below a sprinkler system main drain line. Courtesy: James Taylor, PE, JENSEN HUGHES

Experience has shown that when sprinkler system design features result in additional difficulty or cost in completing ITM activities, building owners often choose to forgo portions of the required ITM procedures over time. Poor ITM practices increase the probability that the sprinkler system may not perform properly when needed. NFPA 25 ITM activities may be accomplished with greater ease and are, in turn, more likely to be completed over the sprinkler system’s lifetime when the system is designed to include features that increase the practicality of ITM. The following describes best practices that may be used to meet some of the NFPA 13 requirements while still facilitating the ITM activities described in NFPA 25.

Inspecting sprinkler system components

Sprinkler system components are required to be visually inspected at regular intervals. For example, NFPA 25 requires quarterly inspections of gauges, control valves, waterflow alarm devices, and supervisory devices. Gauges on dry and pre-action systems are further required to be inspected on a monthly basis. Gauges are inspected to ensure that they are free from physical damage and are displaying normal system pressures. Valves, waterflow devices, and supervisory devices are inspected to ensure that they are free of physical damage. In addition, valves are inspected to ensure that they are maintained in the appropriate orientation (open/closed). This inspection is of particular importance due to the fact that “normally open” valves placed in the closed position are known to serve as a leading cause of sprinkler system failure. According to NFPA’s June 2013 article, “U.S. Experience with Sprinklers,” 64% of sprinkler systems failed to operate during a fire scenario due to system valves being closed. Closed valves serve as a leading cause of sprinkler system failure.

Figure 2: Right: Water rapidly overflows the 4-in. drain during a main drain test. Courtesy: James Taylor, PE, JENSEN HUGHES

All of the aforementioned components are generally located at the sprinkler system riser or at sprinkler system floor control assemblies. Given the frequency of these inspections, the sprinkler system designer can best serve the building owner by locating the risers and floor control assemblies where such devices can be easily viewed, preferably without the need for a ladder. The 2016 edition of NFPA 13 refers to this need in Section 8.1.2 by requiring that system valves and gauges be accessible for operation, testing, and maintenance. The Annex note for this section allows that valves do not have to be in an open or exposed location and may be located behind doors, removable panels, or in valve pits. Given these vague guidelines, one could argue that a valve located 20 ft above a finished floor can be reached by scissor lift and considered accessible.

Most sprinkler system designers and installers locate sprinkler system risers and trim at a height that can be easily reached and viewed for inspection and maintenance. However, in multifloor buildings, floor control assemblies tend to be located near ceiling level either inside a stairwell or outside of stairwells, or above suspended ceilings. To facilitate ease of maintenance and inspections, it is recommended that the system designer locate floor control assemblies inside stairwells rather than above suspended ceilings. Following this rule provides the advantage of easy visibility for inspection, testing, and maintenance and also makes the floor control valve considerably easier to locate in the event of a system accidental discharge. Additionally, it is recommended that the floor control assembly be located no higher than 7 ft above the stairwell landing, where the stairwell landing depth is of sufficient size to accommodate such equipment without impacting required egress width.

In addition to quarterly inspections, a number of components are required to be inspected annually including hangers and seismic bracing, sprinklers, pipe, fittings, spare sprinklers, system information signage, and fire department connections. The majority of these items are located as necessary to meet system design criteria including design density and spacing. The designer, therefore, has minimal control over location for ease of ITM.

Section 8.16.1.1.8 requires identification signs at every control valve to indicate valve function and what the valve controls. While not required by NFPA 13, it is also recommended that valve identification signs indicate whether a valve is intended to be normally open or normally closed. This is one of several sections requiring signage for identifying various components. These signs are vital for better serving building owners, maintenance staff, and responding fire department personnel who may not be fully familiar with the building layout and the details of the building design.

Figure 3: This sprinkler system floor control valve is located more than 15 ft above the top stairwell landing. Notice the door frame located in the bottom right-hand corner of the photo. Courtesy: Julie E. Buffam Brown, PE, JENSEN HUGHES

Testing sprinkler systems

NFPA 25 requires that a main drain test be completed on an annual/quarterly basis (depending upon system configuration) to determine if any degradation of the water supply has occurred. A portion of this test involves fully opening the main drain valve and allowing water to flow for a duration long enough to obtain a stabilized residual pressure before the valve is closed again. To facilitate this test, the 2016 edition of NFPA 13 Section 8.16.2.4.6.2 states that the main drain test connection “shall be installed that the valve can be opened wide for a sufficient time to assure a proper test without causing water damage.” If the final design of the main drain does not permit full flow for a long enough duration, sprinkler system service personnel may be forced to throttle the drain valve, close the drain valve prematurely, or not perform the test at all in an effort to prevent water damage. Ineffective main drain tests may allow a degraded water supply to go unnoticed. 

One common method is to route the main drain discharge to the exterior of the building. Alternatively, practicality or local environmental laws may require that the main drain be discharged to the sanitary sewer. In both cases, a number of factors must be considered by the engineer to ensure that the main drain will be installed to allow for proper testing.

If the drain will discharge to the exterior of the building, the engineer should consider whether the discharge location will negatively impact property, vegetation, building use, etc. Is the discharge location sufficient to prevent water from flowing back into the building? Is the ground surface at the discharge location capable of resisting erosion due to water discharge? Could vegetation, vehicles, or other nearby objects be damaged by the discharge of water? Will the discharge of water outside during the winter months create a dangerous situation, such as an ice-covered building entrance? If discharging to an interior floor drain, it is important to ensure that the test can be completed without negatively impacting the building interior due to flooding or splashing. Can the floor drain handle the anticipated flow? Is the drain located near storage or electrical components? The engineer should estimate the expected waterflow from the main drain. This will depend on the water supply pressure and drain piping size and will drive the necessary size of the interior floor drain. If the drain cannot be sized to fully handle the anticipated flow, then consideration should be given to providing a contained space into which excess water can be permitted to accumulate.


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BRUCE , VA, UNITED STATES, 04/25/17 06:10 PM:

Great Article and will follow your advice to provide proper means of ITM.
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