Carson, California- The roof on the third of three sewage tanks, under construction by Kiewitt Pacific Co., collapsed Thursday, dropping 11 workers about 50 feet into a web of steel rods and wet concrete.
The roof collapsed after workers started pouring concrete atop the structure, said Don Avila, a spokesman for the Los Angeles County Sanitation District.
Two workers were impaled on steel rods used to reinforce the concrete after falling into the tank. One was listed in critical condition. The others had minor injuries.
The workers were trapped by a cement decking that came down on top of them, county fire Inspector Mike Brown said.
Authorities used a crane to lower firefighters and equipment into the tank. The rescue effort was hampered as search crews carefully made their way through unstable rubble.