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Federal inspectors have found that a Big Dig tunnel ceiling that collapsed in July and killed a motorist was designed with a smaller margin of safety than other tunnel ceilings in America, according to a report obtained by the Boston Globe.
The Interstate 90 connector tunnel’s drop ceiling panels were held in place by steel hangers suspended from bolts that were glued into the tunnel ceiling with epoxy. But there were no beams attaching the ceiling to the walls, and there were half as many bolts used as called for in the original design.
“No redundancy was built into the ceiling in the event the hangers failed,” according to a preliminary report by the National Transportation Safety Board obtained by the Globe.
“The NTSB has researched other tunnels throughout the country and has found that significant redundancy is built into the ceiling design” so that the ceilings would not collapse when bolts fall out, the report said. The Globe account appeared in Wednesday’s editions.
The report does not reach conclusions about the cause of the ceiling collapse because the investigation is not finished. The July 10 accident has resulted in a civil lawsuit and other federal and state criminal investigations of the $14.6 billion highway project.