Shakin’ All Over
The importance of earthquake protection for sprinkler systems
NFPA Journal®, May/June 2013
With the 2013 edition of NFPA 13, Installation of Sprinkler Systems, fresh on the streets, one of the most frequent questions I get when teaching the NFPA 13 update classes is, “Do I still need to do all of that confusing seismic protection?”
Of all the requirements in NFPA 13, the ones addressing earthquake protection of automatic sprinkler systems are considered by many to be the most challenging to understand. This is largely because the topics addressed for earthquake protection deal more with the mechanics of materials and other structural engineering issues as opposed to hydraulics, the topic of most of the requirements in NFPA 13. While the requirements of Section 9.3 have a different flavor than the “water-based” requirements in the standard, their importance should by no means be underestimated.
According to the U.S. Geological Survey, between 2002 and 2012 the average annual number of earthquakes in the United States with a magnitude of 5.0 or greater was 62. (By comparison, the rest of the world averaged more than 30 times that number annually.) While not all earthquakes with a magnitude of 5.0 or greater are as significant as the 6.7 magnitude Northridge, California earthquake of 1994, they are significant enough to damage sprinkler systems that are not properly designed to handle these dynamic events.
When an earthquake occurs, the majority of sprinkler system damage is due to the impact of seismic waves. Seismic waves create an initial condition where the base of a building begins moving with the earth, while the upper portions of the building, and its contents and components, remain stationary. Just fractions of a second later, the upper portions of the building will begin to move in the same direction — but by then the base is already moving in a different direction, creating differential movement between the building and its components. This movement can cause a sprinkler system that has not been properly braced to come into contact with other building systems or structural members that can damage the sprinklers and fittings. This damage can lead to leaking throughout the piping network and can impair the system.
Earthquake protection, as required by NFPA 13, Section 9.3, is designed to limit the impact of this differential movement so that the sprinkler system can function as intended after, and potentially during, the seismic event. NFPA 13 uses several design concepts to limit the impact of differential movement, including limiting piping stress through the use of flexible fittings and clearances. To help maintain the alignment of system components and prevent the development of damage-inducing momentum, the standard requires sway bracing and restraint for system piping. When properly designed and installed, these kinds of features can help keep the system in proper working order.
It is critical to have fire protection systems in place after an earthquake, because it is not uncommon to see a higher volume of fires due to ignition sources that become exposed during the seismic activity. These ignition sources include electrical hazards such as disconnected or exposed wires and panels, along with fuel sources that may have spilled due to ruptured tanks or broken piping connections. Leaks involving natural gas and propane are also a source of fire once the gas is ignited. The types of earthquake protection requirements in NFPA 13 can help ensure that the losses associated with a tremor are not exacerbated by fires that cannot be controlled by sprinkler systems that are out of commission.
Matt Klaus is a senior fire protection engineer at NFPA and staff liaison on NFPA 13, 13R, 13D.