Sprinkler System Health

09/06/10

Although residential sprinkler systems have proved to be the most effective form of life and property safety available, annual reports from the National Fire Protection Association show that only 2% of all homes are protected with sprinklers. A new method of installing sprinklers promises to change that.

Multipurpose sprinkler/plumbing systems are now available for private homes in the United States, Canada and the United Kingdom, and they're also being introduced in European nations. The systems have technical, economic and marketing advantages over stand-alone systems, which include overcoming the two biggest barriers to the advance of residential sprinklers: cost and builder resistance.

With these advances, fire chiefs will find it easier to promote residential sprinklers, either with sprinkler ordinances or as optional upgrades for new homes.
Multipurpose systems defined

When the piping for a residential sprinkler system also serves as the plumbing pipe, it's defined as a multipurpose system. The use of one set of pipes for both purposes reduces cost and eliminates the need for cross-connection devices, which are required to prevent contamination of the potable water supply.

The stagnant water in stand-alone sprinkler systems is considered a potential health threat, and public health officials require that they be separated from potable water by check valves or backflow preventers. The type of multipurpose system shown in Figure 1, at right, eliminates stagnant water. The deletion of a check valve or backflow preventer can reduce installation costs from $50-$500.

Multipurpose systems use UL-listed pipe and fittings. They have been in NFPA 13D since the early ’90s, but they didn't gain notice until the 1999 edition. Two key revisions to that edition have increased interest in this method of fire protection. The first revision reduced the minimum working pressure of pipe from 175psi to 130psi. The original pressure requirement had been imported into the original edition of NFPA 13D from NFPA 13, with the justification that sprinkler pipe had to withstand the higher pressures generated through fire department connections.

To push through the revision, supporters of multipurpose systems pointed out that NFPA 13D doesn't require fire department connections. Since the pipe would never experience more than normal plumbing pressures, reducing the working pressure was justified. Plumbers routinely install pressure-reducing valves when the water supply pressure exceeds 70-80psi, so the 130psi requirement is well beyond the expected normal operating pressure.

The other revision reduced the minimum pipe diameter from I-inch to H-inch, the diameter normally used for plumbing systems. NFPA 13D requires the system to supply enough water to flow the two most demanding sprinklers. Supporters of the change documented that the smaller diameter could supply the required amount of water by creating a compound loop system.

The NFPA 13D technical committee accepted the change with additional criteria. It required that the H-inch multipurpose system have a minimum of three paths, which the hydraulic efficiency of the compound loop accomplishes.

Once the water leaves the water supply manifold, it's divided into multiple paths. The water from the multiple paths is recombined at the multiport fitting of the flowing sprinkler. The H-inch system uses a multiport fitting that can receive water from four paths. Where a sprinkler fitting is near a plumbing fixture, one of the four ports is used to feed the fixture. The remaining three ports supply water to the sprinkler.

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