Mayor Kurt L. Schmoke sent 1,200 city workers home at noon yesterday after many complained of fumes wafting from the basement of the Charles L. Benton Jr. Building at 417 E. Fayette St.
Investigators believe the fumes may have been forced into the building by nearby construction of the 1.5-mile-long Metro extension from Charles Center to Johns Hopkins Hospital.
A spokesman for the state Department of the Environment said the fumes, which state inspectors identified as "weathered gasoline," are trapped below the Benton building basement.
Compressed air used to keep ground water out of a nearby subway tunnel is likely to be leaking from that tunnel and forcing the fumes to migrate into buildings along Baltimore Street, according to officials familiar with the project.
Michael P. Sullivan, the Environment Department's spokesman, said the fumes are coming from somewhere under the building, but state inspectors were not certain of the source.
He said there was no threat of an explosion.
From a health standpoint, "it's not something you want to have prolonged exposure" to, he added.
The building will remain closed today, with the workers it houses on administrative leave with pay, public works Director George G. Balog said last night.
"The fumes don't seem to be toxic, nor do they appear to be explosive. But they do cause nausea," Mr. Balog said, adding that the mayor "felt it was better to be safe than sorry."
The fumes, which workers said have been evident for a week, became stronger yesterday, permeating stairwells and offices throughout the 14-story office building.
Mr. Schmoke visited the building, near his City Hall office, about 11:45 a.m. and immediately ordered officials to send workers home until further notice.
David Tanner, zoning administrator, said he began smelling the fumes, similar those from a solvent or cleaning fluid, in stairwells last week. By yesterday the smell had grown stronger and was evident in his first-floor office, he said.
One city worker, who asked not to be identified, said the fumes were so strong last week in the stairwell's upper floors that "I almost passed out. I had a sore throat all week."
City workers Felesa Walls and Gregory Greene said they could smell the fumes in their eighth-floor offices, where some people complained of headaches.
Shortly after employees were evacuated at noon, two city workers carried a large fan into the basement in an attempt to dissipate the fumes.
As of yesterday, subway crews were excavating about 700 feet westof the Shot Tower station, almost directly next to the Benton Building.
"We have to assume it's either a helluva coincidence or somehow we're causing it," said Ken Merrill, construction manager for DKP, the firm overseeing the project for the Mass Transit Administration.
If that proves to be the case, it would be the third time the $321 million subway project has had problems with leaking hazardous materials. Most recently, the MTA shut down excavation in two tunnels near Johns Hopkins Hospital because it was causing gasoline fumes from the site of a former service station to leak into basements near the site.
Work on the Hopkins tunnels is scheduled to resume in about three weeks when construction crews finish sealing the 1,000-foot-long tunnels to prevent any more compressed air from leaking out.
Earlier, tunneling near Hopkins had to be delayed 10 months when crews ran directly into gasoline-soaked sand and experienced some equipment problems in late 1990.
Halting construction at the Baltimore Street site may not be a viable option, however. MTA officials fear that any reduction in the amount of compressed air in the tunnel would cause the surrounding ground water to flood in.
"The better option appears to be to tunnel quickly and get out of there," Mr. Merrill said.