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Author(s): Matt Klaus. Published on May 1, 2017.

Protecting valuable cultural spaces with preaction sprinkler systems

BY MATT KLAUS

If you’re lucky enough to be visiting historic Boston for this year’s NFPA Conference & Expo, I hope you can take the opportunity to visit some of the city’s museums, art galleries, and historic colonial structures. While walking through these spaces and observing the magnificent artwork and historical artifacts is fun for the patrons, designing the systems to protect them can be a significant challenge.

While there are exemptions for historic structures to not require sprinkler systems, most museums and art galleries are required by NFPA 909, Protection of Cultural Resource Properties—Museums, Libraries, and Places of Worship, to be protected by automatic sprinkler systems or alternative fire suppression systems. The code does not specify exactly what type of system needs to be installed; instead, it directs the designer to NFPA 13, Installation of Sprinkler Systems, to draft a code-compliant and functional system. In most light-hazard occupancies, the designer will go to work on a wet pipe sprinkler system and call it a day. For spaces that have historically significant artifacts or priceless works of art, however, a wet system may not be the best choice.

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For situations like this where the designer—or more likely the owner or property underwriting firm—may be concerned about an accidental discharge of water, looking to a preaction system may be the best course of action. A preaction system is a sprinkler system that consists of air-filled piping connected to the automatic sprinkler that is also tied into an automatic detection system located in the room being protected. In order for water to be discharged from the sprinklers, the detection system must be activated and one or more of the sprinklers must also reach its activation temperature.

The two most common types of preaction system are the double-interlock preaction system and single-interlock preaction system. For a double-interlock system, the piping is filled with compressed air. For these systems, the piping will not become filled with water until both the sprinkler and detection system are activated. With a single-interlock system, only the detection system needs to activate to fill the pipes with water. While either of these systems can be installed in a museum or art gallery, the single-interlock system is seen as the most desirable for those types of spaces.

The primary use of the double-interlock preaction system is to protect freezer storage warehouse spaces where filling the pipe with water can be extremely costly. In museums, art galleries, server rooms, and other spaces sensitive to the discharge of water, filling the pipes with water is not nearly as problematic because it can be easily drained without concern for freezing that exists in freezer spaces.

One of the primary advantages of the single-interlock system is that the water reaches the fire much more quickly than in a double-interlock system. The benefit of the faster response is that the fire will be smaller at activation and fewer valuables will be exposed to the fire. This will also cause fewer sprinklers to activate, which will limit the impact of water being discharged within the space.

While NFPA 13 allows both of these systems to be installed, the designer must weigh the pros and cons of the system types when making the ultimate decision on which to choose. Not all system designs are cookie-cutter, out-of-the-box layouts—sometimes the contents being protected require that a system reflect a fair bit of artistry in its own right.

MATT KLAUS is NFPA technical services lead for fire protection engineering. Top Photograph: Getty Images