Fire destroyed two of seven cooling towers Wednesday at the Arizona Public Service plant in Tempe.
An employee noticed smoke about 8 a.m. coming from the west end of the tower structure near McClintock and University drives, said senior fire inspector Phil Rohe. Witnesses said flames shot 20 feet into the air. Police closed access to the plant as firefighters used a ladder truck to dump water on the blaze.
Jeremy Yeaman, an air conditioning technician working at a business across University Drive from the plant, said he saw smoke and at least two sudden bursts of flame. "It was huge," Yeaman said. "The first thing that went through my head is that somebody bombed somebody."
The towers are used to cool steam that drives turbines and changes it back to water. They are made largely of Fiberglas and wood treated with chemicals, such as arsenic, to preserve it, said APS spokesman Mark Fallon.
It is possible some chemical by-product was created in the fire because of the arsenic and sulfuric acids used to treat the water, but not enough to cause alarm, Fallon and Rohe said.
"We had a lot of room for the smoke to dissipate before it got to any residential neighborhood," Fallon said.
The fire, likely due to a turbine fan or gearbox mechanical failure, did not significantly affect power output, officials said. Smoldering embers helped resurrect the fire about 6 p.m., which firefighters extinguished before it could spread, said Deems Shepard, a Tempe Fire Department spokesman.