Collapse of Big Dig Ceiling in Boston Is Tied to Glue

WASHINGTON, July 10 — The ceiling collapsed in one of Boston’s Big Dig tunnels a year ago, killing one woman, because builders used the wrong epoxy to hold the anchor bolts in place, the National Transportation Safety Board said Tuesday.

“We’re talking about the wrong glue here, in effect,” said Kitty Higgins, one of the five members of the board, which said that the epoxy selected dried quickly but lost strength weeks later.

A continuing theme of the board’s meeting Tuesday was how small a detail led to the accident. “It’s kind of ironic in a $14 billion project,” said Deborah A. P. Hersman, a board member. “About $1.50 per anchor is what ended up bringing the ceiling down.”

During construction, the builders tested the strength of the bolts; when some failed, the problem was attributed to installation errors, not breakdown of the epoxy.

“The knowledge of the engineering community seems to be deficient,” said Bruce A. Magladry, director of the board’s office of highway safety.

With concrete, steel and asphalt, he said, “once you test them for strength, they essentially keep that strength forever.”

“Epoxy is not that way, it’s a different material,” Mr. Magladry said.