The demolition of the former Deutsche Bank building has been suspended yet again after two firefighters were injured by a steam pipe from the building that fell through the roof of their firehouse next door.

The accident occurred at around 7 a.m. yesterday and officials said they could not yet say what triggered the fall. The steel pipe, which was used to conduct steam, is about three inches in diameter, and the portion that pierced the roof of the Engine and Ladder 10 building was about 15 feet long, authorities said.

Officials said the pipe carried no contaminated materials and that the firefighters suffered only minor injuries from dust and debris.

Still, the Buildings Department is proceeding with caution in what has become a routine procedure — halting the demolition of the Deutsche Bank tower, which suffered irreparable damage during the September 11, 2001, terrorist attacks.

A host of delays due to litigation, the detection of highly contaminated materials, and a discovery of human bone fragments on the roof have stretched the timeline for the project to years longer than originally anticipated.

Yesterday, a Department of Buildings spokeswoman, Kate Lindquist, said work would be stopped “until the Buildings Department reviews the contractor’s means and methods to ensure public safety.”

She was unable to give a time frame, but a spokesman for the Lower Manhattan Development Corporation, Errol Cockfield, said that contractors would be able to make the deadline to raze the building.

“The timeline is to have it completed by the end of 2007,” Mr. Cockfield said. “We don’t anticipate that this incident is going to affect that.”

Mr. Cockfield said monitors from the local to federal level have been monitoring the site for contaminants on a daily basis, and will continue to do so as the work continues.