An independent examiner has determined that years of heat and sun exposure to aging bladders caused the damage that led to a section of the western dam at Tempe Town Lake giving way on July 20.
SEA Ltd. inspected one of the 11-year-old dam bladders at its Columbus, Ohio, facility and concluded in a nine-page report that "intra-carcass pressurization" - separation of internal layers - led to the burst.
"Experts in the field have cited the age and heat combination as the reason," said Jeff Kulaga, Tempe assistant city manager. "We are accepting that evaluation and are moving forward."
Before the burst, Kulaga said, Bridgestone determined that the bladders were deteriorating faster than expected and arranged an agreement with Tempe to replace them at no cost to the city.
"The jointly-commissioned report confirms what Bridgestone said as early as 2007 about the climate conditions and the long-term effects the environment has had on the rubber bladders in Tempe," James Wheeler, director of operations and finance for Bridgestone, said in a statement.
The four bladders are being replaced - the lake is expected to open in early November - and precautions will be taken to protect them from the sun.
They will be shaded by a new pedestrian bridge, and a sprinkler-watering system will provide additional cooling.
Under those conditions, the bladders should last for the duration of a five-year lease agreement between Bridgestone and Tempe. By November 2015, a long-term dam structure will be in place, and Kulaga said that a bladder system and a steel-hinge gate are among the options.
"The report from SEA and our experience with rubber bladders will all be taken into account in our future analysis of a (long-term structure)," Kulaga said.