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BOSTON—The National Transportation Safety Board (NTSB) issued in early November an update on its investigation into the July 10, 2006, ceiling collapse of the I-90 connector tunnel in Boston. A portion of the ceiling located in the tunnel’s east portal detached from the roof of the tunnel and collapsed onto a passing automobile, killing the passenger and injuring the driver.

The NTSB said its investigation has branched into two primary areas of interest—the engineering aspects of the suspended ceiling, and issues associated with construction management and oversight of the ceiling system. 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.

According to an NTSB report provided by the Boston Globe, ceiling panels that were installed with epoxy anchors in the adjacent Ted Williams tunnel were lighter weight, made from metal sheets with a porcelain coating. Heavy concrete panels similar to those that fell were used in another tunnel, but were attached with traditional "nut and bolt" assemblies to a steel uni-channel cast into the tunnel’s concrete roof. The connector tunnel was constructed without uni-channels. Nevertheless, according to the NTSB report, a decision was made to install the heavy concrete panels using only epoxy anchors. In addition, the NTSB reported, no redundancy was built into the ceiling design in case the hangers failed.

Investigators examined 20 anchor holes where the collapse occurred and documented the downward displacement of all of the anchors in the eastbound and westbound tunnels, as well as in the HOV tunnel. All of the tunnels had a substantial number of displaced anchors, according to the NTSB, and some of the anchors in the westbound tunnel had displacement greater than 1 inch.

The NTSB performed a chemical analysis on epoxy taken from the failure area and compared the results with analyses of the fast-set and standard-set epoxies produced by the manufacturer. The National Institute of Standards and Technology is performing visco-elastic characterization of the epoxy materials to help understand the long-term creep behavior of the material.

Interviews with construction personnel indicated some discrepancies between the construction contract and the actual procedures used to test epoxy anchor pullout strength. Potential problems also were noted with procedures used to install the ceiling modules. NTSB investigators have not found any records indicating that tunnel inspections of the ceiling system were conducted from the time it opened to traffic in January 2003 to the day of the collapse.

NTSB investigations continue into the relationship between the state of Massachusetts, the Federal Highway Administration, and Bechtel/Parsons Brinckerhoff’s roll as program manager. 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.