About 350 workers were evacuated from three buildings at the Johns Hopkins University Applied Physics Laboratory in Howard County and sent home yesterday morning after they noticed sagging ceiling tiles caused by roof stress under the weight of the weekend's huge snowfall.
By late afternoon, though, engineers had decided the buildings could be reoccupied, saying that the steel beams running through the structures were reacting as expected to the 15 inches of snow melting on the flat rooftops.
"They are convinced that it is a safe environment," said Helen Worth, APL's public information officer.
The incident was one of a number of emergency responses across the Baltimore region yesterday to potentially dangerous loads left on roofs by the record snowfall.
From Baltimore to Carroll and Harford counties, buildings were evacuated, and dangers were assessed.
In Carroll County, a medical building in Eldersburg was evacuated in the morning after sensors in a roof of the building indicated that it was unstable, said the Maryland State Police at Westminster.
In Harford County, the Weis grocery store at Route 24 and MacPhail Road had to be shut down after heavy snow on the roof caused a door to pop off its tracks, raising concerns that the pressure on the glass could blow out windows, said county inspections chief Richard Lynch.
In Baltimore, officials said that a beam had cracked at the Downtown Partnership building at 217 N. Charles St. but that earlier reports of a roof collapse were false. The building was ordered evacuated and closed until today.
A total of 120 people fled the five-story building about 11:45 a.m. Workers at a development company on the fifth floor noted that a conference room ceiling was bowing, said a spokeswoman for the Downtown Partnership. She said Fire Department officials recommended that they evacuate the building.
At the Hopkins lab, employees, some of whom work in the space and power projection departments, others in administrative departments such as travel and retirement, were cleared to return to work by 5 p.m.
The buildings, all single story with drop ceilings, are not part of APL's main campus off Johns Hopkins Road off Route 29 just south of Columbia but are leased in the adjacent Montpelier Research Park, officials said.
APL employees who arrived at work by 8:30 a.m. - the first time the lab has been open since the storm - sounded the first alarm. Within an hour and a half, the structures had been cleared and the original building engineers called in to evaluate the potential for collapse.
The engineers determined that the weight created a "give" that was about half what was allowable, Worth said.
State troopers were dispatched about 11 a.m. to the South Carroll Medical Center, a single-story, flat-roofed building in the 1300 block of Progress Way near Route 32, after a call from the building management company, said Lt. Terry L. Katz.
The building houses medical offices and is an annex of Carroll County General Hospital.
A county building inspector arrived about 20 minutes later and determined that the building was not safe and could not be inhabited, he said. "The problem was in the southwest corner, where a steel beam was bowed by weight of snow," Katz said.
David Horn, director of marketing, business development and managed care at the hospital, said about 25 medical staff members and patients were evacuated as a precaution. The roof was sagging in a few areas, he said. He immediately contacted a structural engineer, who determined that the sway in the roof was well within the threshold for safety and that once the snow was removed the roof would return to normal, Horn said.
Horn planned to have crews with shovels and snow blowers clear the roof throughout the evening. "We expect to be open in the morning."
Structural engineers in Harford were assessing how to safely remove a 6-foot to 8-foot snowdrift on the roof of the Weis grocery store, Lynch, of the county inspections office, said, adding the store would remain closed until repairs could be made.
He said employees noticed buckling in the front wall Monday night but didn't realize the potential gravity of the situation until yesterday: "After seeing the symptoms [of an overloaded roof], we didn't want a store loaded with shoppers."
Sun staff writers Lane Harvey Brown, Mary Gail Hare and Sheridan Lyons contributed to this article.