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Life Safety in a Seismic Zone CPVC Supports Post-Earthquake Fire Suppression
September, 2007
By Matthew Kuwatch
A fire sprinkler system offers little or no benefit if it doesn't remain intact when an earthquake strikes. Thus, the International Building Code addresses the installation of fire sprinklers in seismic zones. A new report also reinforces earlier field findings suggesting that a fire sprinkler system made of chlorinated poly vinyl chloride (CPVC) is more likely to perform reliably during and after an earthquake than a steel system.
Based on observations documented since 1990, approximately 17 major earthquakes occur across the globe in one year. On October 10, 1986, the U.S. embassy in San Salvador, El Salvador, was situated near the epicentre of one such earthquake, which lasted seven seconds and measured 7.5 on the Richter scale.
Damage was significant, with thousands of casualties. At least 200 buildings in San Salvador were destroyed or severely damaged, including many of the buildings in the U.S. embassy complex.
The five-storey chancery was one of the hardest hit and had to be immediately abandoned. The force of the tremor was so severe that a number of one- and one-quarter inch-thick steel reinforcement bars embedded in the building's concrete support columns were bent into the shape of pretzels.
Despite all the damage, the recently retrofitted CPVC fire sprinkler did not fail. Post-earthquake assessment determined that the entire system stayed substantially on-line without any leaks, and would have suppressed any fire in the complex caused by the earthquake.
Not only did this mean continued safety for the occupants, but it also turned out to be a reliable source of drinking water. Due to the complete failure of the municipal water supply, the sprinkler water supply became a readily available and convenient source of water for domestic use.
As a result, the U.S. Department of State Embassy Buildings reported that the non-metallic CPVC sprinkler pipe had performed "admirably" during this major earthquake, especially considering that the main building had suffered severe damage and all other HVAC and plumbing systems were destroyed.
TEST RESULTS
More recently, Wiss, Janney, Elstner Associates, Inc. (WJE) - a national engineering, architectural and materials testing company - tested the performance of CPVC pipe and fittings and compared it to the performance of steel pipe (1-inch in diameter) using cyclic loading. After 50 cycles, the CPVC system remained intact, whereas the steel pipe failed at a 90-degree elbow after approximately 33 cycles.
The test setup consisted of suspending the piping from dimensional lumber connected to steel framing, which was anchored to the structural lab floor. Pipe support hangers were spaced six feet for each pipe. The test configuration consisted of installing 1-inch diameter CPVC pipe in a Z-shape with two 90-degree connections to the test framing. Steel pipe 1-inch in diameter was assembled independently in the same design configuration.
The hangers on one side of the framing were positioned and connected to the wood members such that this section of the piping was allowed to slide during loading. The pipe was filled with water and pressurized to 175 psi before the start of each test. Displacement of the pipe was controlled using a hydraulic actuator. A load cell was in-line with the actuator and pipe to measure the force required to move the pipe.
Both types of pipe were displaced a maximum of plus/minus three inches, or a total displacement of six inches, during which time the connections were monitored for water leakage. The actuator moved at a frequency of 0.04 Hz (or approximately two cycles every 50 seconds) for a period of nearly 20 minutes.
After 50 cycles, elbow connections and fitting along the CPVC pipe length were still secure, and the pressure remained at 175 psi throughout the test. The steel pipe's failure after 33 cycles created a loss in pressure and caused water to spray out of the joint connection. Upon careful analysis, it was determined that a fatigue failure had occurred at the elbow threaded connection.
Through the years, building codes have become increasingly more demanding with regard to the installation of fire sprinkler systems in seismic zones. This is partially due to the fact that the 1990s saw a pronounced increase in both the frequency and intensity of earthquakes compared to earlier decades. The National Earthquake Information Centre estimates that there are several million earthquakes occurring in the world each year, although many go undetected because they hit remote areas or they have a small magnitude.
From a life safety perspective, the objective 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. That makes tests such as the one conducted by WJE important, although the real test is how the system performs in the real world.
Matthew Kuwatch is Global Marketing Manager for BlazeMaster( CPVC Fire Sprinkler Systems, and Executive Director and Vice Chairman of the Steering Board for the Ohio Fire Safety Coalition. For more information, see the web site at www.blazemaster.com.
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