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Sprinkler System Health
02/09/12
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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