How to Hold Your Water When the Earth Shakes

New Seismic Fire Sprinkler Regulations Are Affecting 80 Percent of U.S.

by Norman J. MacDonald III

In the U.S., more than 80% of the states have adopted new provisions of the International Building Code, which address the installation of fire sprinklers in seismic zones. However, many engineers and specifiers are unaware of the requirements and how best to comply with the codes.

Briefly, the state codes are intended to prevent the likelihood that a fire sprinkler system will become damaged and rendered inoperable by seismic activity that causes ceiling movement to shear heads and/or disrupt the integrity of armover connections to branch lines or mains. An in-depth study of the performance of fire-sprinkler systems during the 1994 Northridge earthquake informs many of the standards (Analysis of Fire Sprinkler System Performance in the Northridge Earthquake, Russell Fleming, NFPA, National Institute of Standards Publication NIST-GCR-98-736.)

In general, depending on the seismic zone rating of the building location, the codes direct either 0.25-in. (6 mm) or 2-in. (50 mm) minimum horizontal clearance between sprinkler heads and suspended ceilings to accommodate the differential in movement of these two elements during a seismic event.

The objective, of course, is to maintain the ability of the sprinkler system to manage post-earthquake fire hazards and prevent significant water damage that can occur from sprinkler-system ruptures in an otherwise undamaged building. Factory Mutual (FM), for example, reported that three of the earthquakes which occurred between 1987 and 1994 caused 144 sprinkler leakage losses covered by FM. The average loss was $212,000, for a gross total of $30 million in 1995 dollars. Both the safety and the economic incentives are obvious.

Therefore, to meet code requirements, hard-pipe sprinkler heads that are installed in suspended ceilings must have the requisite clearance. In the most-stringent zones, the standards mandate that either a rigid brace be used to limit lateral deflections of the ceiling or that sprinkler heads have a 2-in. (50 mm) oversize ring, sleeve or adapter through the ceiling tile to allow for at least 1 in. (25 mm) of free movement in all horizontal directions. As an alternative, a swing joint that provides the same horizontal movement can be installed at the top of the sprinkler head extension.

An Easier, More Effective & Less Costly Solution

In every zone, flexible fire sprinkler systems provide characteristics that exceed the seismic code requirements, provided that the correct length of flexible hose is specified. As the name suggests, flexibles connect the sprinkler head to the branch or main via a length of reinforced flexible hose. This allows the head to move in any direction during a seismic event, as well as in the natural settling that might occur as construction ages.

The International Building Code, the American Society of Civil Engineers (ASCE) standards and the National Fire Protection Association standards (NFPA) all include provisions that acknowledge the applicability of flexible fire sprinkler systems in seismic areas. For example, ASCE notes that a viable alternative to providing large clearances around sprinkler system penetrations through ceiling systems is for the sprinkler system and ceiling grid to be designed and tied together as an integral unit. In the appendix of NFPA 13, 2007 edition, the committee states that flexible hose connections may be attached to suspended ceilings because it allows the necessary deflections under seismic conditions.

The typical flexible system, described further below, includes a mounting bracket that enables the sprinkler head to move in unison with the ceiling grid. It is important to note that a swing joint in a hard-pipe installation accommodates only horizontal motion, whereas the flexible connection can rotate and move in any direction.

In addition to simplifying code compliance and achieving the desired durability of integrity, this also means that there is no installation premium for flexible systems in seismic zones, as there is with traditional hard-pipe systems. Furthermore, the sprinkler installation maintains the aesthetics of a "normal" building.

Invented to Meet Extreme System Integrity Requirements

The first viable flexible fire sprinkler connections were developed by FlexHead Industries, Holliston, MA, for semiconductor manufacturing facilities. Initially designed for exhaust-duct protection, the technology was later adapted for suspended ceilings in cleanrooms. The flexibility of the connection eliminated concerns about hard-pipe armover joint leaks or particulate generation caused by seismic activity or building shifts. In addition, the technology provided fast-track construction and the ability to easily accommodate future space changes. High-quality, welded stainless-steel construction and a custom-designed fit-up also contributed to the extreme system integrity demanded in cleanroom environments.

Several years ago, the technology was adapted for use in suspended ceilings commonly found in commercial projects. Currently, a handful of manufacturers offer flexible connections that employ various design, materials and construction approaches. Typically, the units consist of a threaded pipe-nipple to connect to the main or the branch feeder line, flexible connecting hose in standard lengths, a reducing fitting that is attached to the sprinkler head and a mounting bracket that affixes to the ceiling grid.

Regardless of design and construction, flexible connections offer consistent advantages as opposed to traditional hard-pipe armovers, particularly in seismic areas. For example, flexible connections involve fewer joints between the branch line and the sprinkler head, which both eliminates most of the handwork that a hard-pipe armover requires and also substantially reduces the potential for leaks.

Flexible Approaches to Flexibility

It is necessary to consider several comparison points within the realm of flexible sprinkler connections that affect cost (initial, installed and lifetime) and performance. These variables include the material used, the design and the degree of factory vs. on-site assembly required.

The most-obvious feature-and an important delta-is the hose. A 1-in. "true" inner diameter, corrugated stainless-steel hose offers the best coefficient of friction, as well as superior resistance to corrosion over time. The strength of the hose and its resistance to reverting to its original shape under pressure both are greatly enhanced by a braided sheath. In fact, only braided hoses can pass the stringent testing that FM requires for certification. As in the hose itself, the sheath material used also affects performance.

In addition, it is important to consider how the system elements are joined: hose, fittings and sprinkler head. While some flexible systems use O-ring joints between the hose and the fittings, others use welded joints. With regard to the reducing fitting that the sprinkler head is attached to, some manufacturers swage pipe and then thread the reduced inside diameter. Other manufacturers machine their fittings from solid stock, which produces consistent tolerances and durability.

Some flexible systems are pretested at the factory and delivered fully assembled, which makes joint integrity more reliable. Other systems are delivered as component parts that must be assembled on-site. Factory pretesting is not possible when the components are assembled on-site-that said, it is necessary for contractors to verify joint integrity.

The final piece of a flexible sprinkler connection assembly is the mounting bracket that attaches to the suspended ceiling grid. Some mounting brackets are single-piece units whereas others comprise subcomponents that require on-site assembly. As with other field-assembled components, this approach to the mounting bracket can make it more susceptible to seismic activity and potential building shifts.

Conclusion

Regardless of manufacture, flexible connections deliver superior benefits as opposed to traditional hard-pipe systems even in nonseismic zones. Using flexibles, engineers and specifiers get the added benefit of doing nothing different to meet even the most-stringent seismic zone codes.

Norman J. MacDonald III is CEO and founder of FlexHead Industries, Holliston, MA. He also serves as Principal Board Member of NFPA 318 and NFPA 13. He can be reached at (800) 829-6975 or via e-mail at nmacdonald@flexhead.com.