A key player in this accident is the scaffolding, or falsework. That's the temporary support structure that was holding up the new bridge until last summer when the weight was transferred to the cable. What we don't know yet is what role the dismantled section of falsework played in this accident.
The neck of the toppled crane fell across the water onto an adjacent barge, with a section of falsework or scaffolding also landing there.
Caltrans can't confirm if the crane was holding the falsework when the accident happened. But the crane was involved in removing the steel from underneath the bridge, one section at a time.
Witnesses on Treasure Island heard the accident happening before they saw it.
"My initial reaction was, oh the underpinnings, they're taking them down and dropping them on the barge," said Dave Guinther with the Treasure Island Sailing Center. "Then it kept getting louder. Then we looked over and, you know, pieces were coming down, the crane was tottering, then it actually fell down."
Roger Ladwig with the Treasure Island Marina adds, "I heard this grinding, I thought it was a plane flying overhead but it just kept going. When I turned around, the crane was already gone and the scaffolding was falling over and then it just fell off the bridge and onto the barge."
Ladwig has been watching the bridge project for years from his office at the Treasure Island Marina. For the last few weeks he'd been watching falsework removal.
"There are two cranes and they're on opposite sides of the scaffolding and they lift up a section of the carrier to hold the scaffolding in place, then they cut it loose and they lower it down," Ladwig said. "When I looked over, one crane was gone, and the scaffolding then collapsed onto the barge."
Witnesses at the Treasure Island Sailing Center raced to help, thinking someone must be hurt.
"The guys that were here from like Richmond Yacht Club and St. Francis, they got in their boats and immediately went over there, were over there in 30 seconds," Guinther said. "Nobody seemed to be hurt, there wasn't any problem that they could deal with, so they came back."
No injuries were reported. And officials with the Metropolitan Transportation Commission (MTC) say the accident should not delay the new bridge opening scheduled for this Labor Day weekend.
"The process of removing the falsework has been set back for at least this afternoon and perhaps longer," said MTC spokesperson John Goodwin. "But again that's a months-long project which is not on the critical path to opening up the new bridge."
Back in the old days when the original Bay Bridge and the Golden Gate Bridge were built, the sort-of accepted formula was one fatality per every million dollars of a construction project. The new Bay Bridge is a $6.5 billion project. They've had zero fatalities, this was the first significant accident since work first began in 2002.