National Transportation Safety Board
Office of Public Affairs
The National Transportation Safety Board continues investigating the circumstances of the July 10th ceiling collapse of the Interstate 90 (I-90) connector tunnel in Boston, Massachusetts. A portion of the ceiling located in the tunnel's east portal became detached from the roof of the tunnel and collapsed onto a passing automobile, killing the passenger and injuring the driver. "The Safety Board is pleased with the progress of the investigation and is making great strides to determine what happened in this accident," said NTSB Chairman Mark Rosenker. "We have received tremendous cooperation from all parties to the investigation."
The NTSB's investigation has branched into two primary areas of interest. The first deals with the engineering aspects of the suspended ceiling. Investigators are looking at how the use of this particular ceiling design evolved, as well as how it was installed and what quality control programs were used during construction. The other aspect of the Board's investigation is concentrating on those issues associated with construction management and oversight of the ceiling system.
Core samples have been taken from the roof in the westbound tunnel, away from the accident location (the accident was in the eastbound tunnel). The examination and documentation of these initial core samples has been completed. Additional core samples from other areas within the tunnel, including samples from the accident location, have been sought, but are awaiting an analysis of the safety implications of their removal.
Investigators have examined twenty anchor holes where the collapse occurred. The downward displacement of all of the anchors in the east, and westbound tunnels, as well as the HOV tunnel has been documented. All of the tunnels had a substantial number of displaced anchors, and some of the anchors in the westbound tunnel had extreme displacement (greater than 1 inch).
The Safety Board is still working to determine the type of epoxy used in the ceiling. A chemical analysis has been performed on epoxy taken from the failure area. Results from this analysis have been compared with analyses of the fast set and standard set epoxies produced by the manufacturer.
The NTSB is consulting with the National Institute of Standards and Technology (NIST) to perform visco-elastic characterization of the epoxy materials, which would help the Board to understand the long-term creep behavior of the material.
NTSB investigators have not found any records indicating that tunnel inspections were done of the ceiling system from the time it was opened to traffic to the day of the collapse. The Board is researching the American Association of State Highway and Transportation Officials (AASHTO) and Federal Highway Administration (FHWA) guidelines on tunnel construction to see if there are any required inspection schedules. The required inspection schedule for bridges is typically every two years.
"We seek to learn as much as possible from this tragic accident with the aim of making recommendations to prevent similar accidents in the future. We will keep the public informed with periodic updates", said Chairman Rosenker.
Other agencies, including the Massachusetts Attorney General's Office, the Department of Justice United States Attorney's Office and the Department of Transportation's Office of the Inspector General are also conducting investigations.
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The National Transportation Safety Board (NTSB) is an independent federal agency charged with determining the probable cause
of transportation accidents, promoting transportation safety, and assisting victims of transportation accidents and their families.