A 40-foot section of floor in Boston City Hall suddenly buckled Wednesday afternoon, breaking a stretch of reddish tile that shattered with a loud crack.
No one was injured, and city officials said the bunker-like concrete building remained structurally sound. The rupture occurred about 3:30 p.m. on the second-floor mezzanine, interrupting the monotony for people waiting in line to pay tickets or renew parking stickers.
The crack ran from the birth certificate counter, past the death certificates, and ended at a stairwell. A clerk told a security guard that it sounded like a car had been dropped in the lobby.
“It was loud,” said Kate Norton, press secretary for Mayor Martin J. Walsh. “People on staff here said it sounded like a bunch of bricks breaking.”
The birth and death certificate counters are normally closed Wednesday, so people were not standing in line where the floor cracked.
The mezzanine has buckled at least three other times in the last 20 years, city officials said. City Hall opened in 1969 and was constructed without expansion joints that give the concrete space to expand and contract with changes in temperature.
Built in the Brutalist style, City Hall has been lauded by some architecture critics but is loathed by many other people because the concrete walls make the entire nine-story building feel like a musty basement. In his bid for mayor, Walsh pledged to tear down City Hall. But the break in the floor was not the work of the mayor trying to make good on a campaign promise.
“This is a result of concrete underneath the floor tiles expanding and contracting,” Norton said. “We are going to get a structural engineer in here to make sure the concrete underneath is safe. We anticipate that it is, because this has happened a few times before.”
Birth and death certificates will be available Thursday, Norton said.Andrew Ryan can be reached at email@example.com. Follow him on Twitter @GlobeAndrewRyan.