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In today’s built environment, the growing emphasis on water-based fire protection systems challenges plumbing engineers to provide adequate pressure and flow while protecting the potable supply from potential chemical or biologic contamination.
The country’s predominant construction safety codes, the International Building Code (IBC) and International Fire Code (IFC), have numerous requirements for fire sprinkler and standpipe systems in buildings ranging from warehouses to high-rise office buildings. In those communities that adopt the International Residential Code (IRC) without amendments, fire sprinklers also are required in one- and two-family dwellings and townhouses.
As the recognized public safety value of built-in fire protection increases, so do the opportunities for cross-contamination. Since the 1970s, major steps taken by government and industry have made huge strides in protecting our drinking water, but the job will never be done. All parties that use water have an obligation to protect its quality.
Table 1 summarizes some historic cross-contamination incidents. Fortunately, according to the American Backflow Prevention Association’s website, only one cross-contamination episode since 2008 was attributed to a fixed fire protection system.
Fire protection standards
When the International codes require water-based fire protection systems, in most cases the user is directed to one of the National Fire Protection Association (NFPA) standards for design and installation. These standards all acknowledge the water purveyors’ requirements for cross-contamination control and caution fire protection designers to factor the influence of various backflow prevention devices into their system plans.
The IFC also requires that new and existing water-based systems be inspected, tested and maintained on a regular basis to enhance their reliability and prevent problems from occurring during an emergency. The primary reference for this work is NFPA 25, Inspection, Testing and Maintenance of Water-Based Fire Protection Systems. An important part of the regular fire protection testing is the “full-forward flush” to verify that the backflow prevention device will open fully to allow the fire protection water demand to be achieved.
According to the NFPA’s Russ Fleming:
Since its 1994 edition, NFPA 13, Installation of Sprinkler Systems, has required that “means be provided downstream of all backflow prevention valves for flow tests at system demand” to facilitate the forward flow test. While NFPA 13 presents this as a performance-type requirement and does not specify the means, the annex has, since the 1996 edition suggested possible options, such as a test header or other connection downstream of the backflow device or a bypass around the check valve in the fire department connection with a control valve in the normally closed position. Basically, any option that can flow the amount of water needed by the sprinkler system is acceptable.
Code officials are well aware of the hydrostatic and flush tests for new fire protection system installations, but may not be as well versed on dealing with flushing requirements for existing systems.
How can this be addressed in the “real world?” Perhaps most important is increasing awareness for code enforcement officials and fire protection contractors that this requirement exists. When fire protection system plans are submitted for review and permitting, the code official should pay close attention to the backflow prevention device’s make, model and nominal size, the fire protection systems anticipated volume and pressure demand and test outlet location(s).
Furthermore, there are three distinct services for which the property owner (or designated representative) is responsible: inspection, testing and maintenance. Explaining these differences — and the costs associated with each — is an important element in achieving compliance.
“Inspection” is visual examination of a system or portion thereof to verify that it appears to be in operating condition and is free of physical damage. Reduced pressure and reduced pressure-detector valves are to be inspected weekly, with a separate, more detailed inspection monthly. Backflow prevention assemblies must be inspected internally every five years to verify that all components operate correctly, move freely, and are in good condition.
“Testing” is a procedure used to determine the operational status of a component or system by conducting periodic physical checks, such as waterflow tests, fire pump tests, alarm tests and trip tests of sprinkler valves. All backflow preventers installed in fire protection system piping must be exercised annually by conducting a forward flow test at the minimum flow rate required for the fire protection system*. Generally, this cannot be accomplished through the two-inch main drain line, and, as cited above, may require a test header or bypass assembly. The forward flow test is not required where annual fire pump testing causes the system flow rate to flow through the backflow preventer device.
“Maintenance” in water-based fire protection systems, is the work performed to keep equipment operable or to make repairs and should be accomplished in accordance with the backflow prevention device manufacturers’ guidance.
* Where water rationing is enforced during shortages lasting more than one year, an internal inspection of the backflow preventer to ensure the check valves will fully open is permitted in lieu of conducting the annual forward flow test.
Meeting the full flow criteria
One important data point is understanding what flow is required to satisfy the “full flow” test. In a hydraulically calculated system, this is relatively easy: the data should be provided on the hydraulic nameplate attached to the system riser (see Figure 1). The nameplate includes the minimum flow (including fire hose stations) and pressure needed to achieve the full flow. If the nameplate is blank or missing, the fire protection contractor should be able to retrieve the design data from the project documents. For an older “pipe schedule” sprinkler system, the tester will have to compute the estimated required flow based on the system requirements when it was installed.
As a rough estimate, it takes one 2 1/2–inch outlet for every 250 gallons per minute (gpm) of required flow. The 2-inch main drain outlet — used for conducting a separate “main drain” test — may not provide enough capacity to satisfy the full flow test, except for very small systems such as those found in one- and two-story apartment buildings.
Data compiled by U.S. Air Force property maintenance teams shows the flows through 2-inch main drains at various residual pressures (see Table 2). During periodic main drain tests, they measured the residual pressure at the sprinkler riser (taken when water was flowing) and computed the volume in gpm through “long” and “short” drain outlets. “Long drains” is a subjective descriptor applied to drain lines more than 20 feet long, measured from the discharge side of the 2-inch drain valve. The flow results take into account the usual number of elbows and fittings found in a 2-inch drain line.
Figure 1, captured in a low fire-hazard church, shows that the minimum flow to satisfy this sprinkler system is 337.5 (gpm) plus 100 gpm for hose streams establishing a total flow requirement of 437.5 gpm. This flow has to be achieved at 36.32 pounds per square inch at base of the sprinkler riser. The flow requirement exceeds the capacity of the 2-inch main drain, so either a combination 2 1/2–inch outlets or a larger diameter outlet will be needed to meet the demand.
When this condition occurs, there are several common options available, which include (but are not limited to):
A bypass installed around the check valve installed in the piping between the system and fire department connection (FDC). The bypass would include a supervised valve in the normally closed position. During testing, the contractor would flow out the outlet of the fire department connection through the appropriate hose and nozzle configuration.
Multiple outlets on the system side of the back-flow device. The outlets would look similar to a hose or 2.5-inch standpipe connection.
A test header, similar to those on systems, which utilize a fire pump.
If the hydraulic nameplate is blank or missing, the fire protection contractor should be able to retrieve the design data from the project documents. For an older “pipe schedule” sprinkler system, the tester will have to compute the estimated required flow based on the system requirements when it was installed.
Regular inspection, testing and maintenance are essential to the proper performance of fire protection and life safety features. They are equally important to water quality protection equipment to avoid cross contamination. Regular and competent full forward flush testing for fire sprinkler and standpipe systems satisfies both of these needs.