Portions of the heavily-traveled Maze will close for weeks, if not months, likely creating traffic congestion not encountered by East Bay commuters since the 1989 Loma Prieta earthquake.
"The heat from the wreckage caused the ramp connecting eastbound Interstate 80 to eastbound Interstate 580 to melt and collapse," Caltrans spokesman Jeff Weiss said. "The temperature during the fire exceeded 2,000 degrees."
The tanker carried 8,600 gallons of unleaded gasoline. The fire burned for about three hours after the 3:41 a.m.
While structural steel melts at 2,700 degrees Fahrenheit, the metal in the ramp was already under stress from the concrete roadway. It folded like taffy on to the ramp below.
"As we were coming down the steps ... we could see an orange glow and a huge column of black smoke," said Oakland firefighter David Yi, whose engine company responded to the fire. "We knew it was something big."
The tanker driver, 51-year-old Woodland resident James Mosqueda, survived with minor injuries. He left the scene before police arrived, by crawling out the truck's passenger window and walking down the ramp to a gas station.
From there he took a taxi to Kaiser Permanente Medical Center in Oakland, Highway Patrol Officer Trent Cross said. Mosqueda was treated later Sunday at St. Francis Memorial Hospital in San Francisco for second-degree burns on his face and hands.
Mosqueda worked the past 10 months for Sabek Transportation, a South San Francisco trucking firm. He left a Benicia oil refinery en route to a gas station on Hegenberger Road, but apparently took a freeway ramp from westbound I-80 to southbound Interstate 880 too fast, Highway Patrol Officer Trent Cross said.
He crashed, and the tanker burned. The skyway above that ramp, which connects eastbound I-80 to eastbound I-580, collapsed on to the lower roadway.
Officers examined skid marks, debris and the damaged guardrail to estimate the truck's speed. Cross said the CHP has not decided whether to arrest Mosquedo.
"If this had happened during weekday commute times, we would have had a very ugly incident on our hands," Cross said, adding that it was fortunate that no one was killed or seriously injured in the accident or subsequent collapse of the ramp.
"The bridge is replaceable. A life is not."
The Oakland Fire Department sent two ladder trucks and five engines to the two-alarm blaze. Because Caltrans had already blocked the unstable freeway when crews arrive, and because fire crews could not find a water source, they initially planned to let the fire burn itself out.
But they eventually found a hydrant below the freeway, and trucks drove under the blaze and sent firefighters up their ladders with hoses, Yi said. Engines fought the fire for about three hours.
"We could see the overpass crumbling and giving way. Bricks were falling," Yi said. "We didn't know what we were dealing with inside the tanker."
Details of Mosqueda's driving record were not available Sunday. His employer, Sabek, was involved in a June 2006 crash in Vallejo that sent about 4,000 gallons of diesel into storm drains. In that case, a double tanker overturned on a ramp connecting I-80 to Interstate 780.
Weiss said Sunday the agency has demolition contractors ready to remove the damaged sections of the Maze, but he did not know when either affected ramp would re-open.
"Some of the fuel traveled through the drainage pipes and ignited" in the lower roadway, Weiss said, "so it is possible that the westbound I-80 to I-580 connector ramp also was stressed from the heat and could be structurally impaired."
The lower ramp carries about 35,000 cars daily, while the collapsed ramp carries about 30,000 Weiss said. The upper ramp was built during the 1950s, while the lower was re-built and widened during the 1990s.
A tanker explosion near the same spot closed the freeway, killed one and injured at least seven in February 1995.
Like Sunday's crash, authorities said at the time that unsafe speed on the twisty skyway connecting westbound I-80 to eastbound I-580 caused it.
The crash breached the tank in that case, and sparks from the truck rubbing against metal railing probably ignited the butane-petroleum mixture inside, causing an explosion.
While nobody died Sunday, the roadway fared much worse than it did in 1995.
"The explosion directed the energy in all directions in the previous case," Weiss said. "In this case, the fire directed a tremendous amount of energy directly up."
The fire erupted under a structural Achilles' Heel of the skyway: The underside, where bare steel support girders and other metalwork are unprotected by concrete.
"I think this was really the perfect fire, tragically," said Abolhassan Astaneh-Asl, a civil engineering professor at UC Berkeley.
Steel supports become elastic like rubber at about 1,000 degrees Fahrenheit, said Astaneh-Asl, who studied the World Trade Center collapse for the National Science Foundation and also studied the MacArthur maze after the 1989 Loma Prieta earthquake.
"When steel gets that warm, it loses its strength and cannot carry its load any more," he said.
San Francisco Mayor Gavin Newsom was working with regional and state officials "to ensure that the transportation needs of the region are addressed" expeditiously, according to a statement released by his office Sunday.
"There's not a lot of slack in the system," Weiss said. "The Maze is very busy, and when other routes have to take on more traffic because of something like this, they all tend to become heavily congested."
MediaNews staff writers Leslie Griffy, Karl Fischer, Scott Marshall, Meera Pal and Ian Hoffman contributed to this story.