Instead, smoke and debris escaped and shot up into the air and window glass shattered. Nobody was injured, but work will be halted until the team provides a decking system review and recommendations for how it will proceed.

The MTA's Capital Construction Co. plans to retain an independent safety consultant, add protective rubber matting and "be much more involved in understanding what the various methods are and how [the contractor] is going to be blasting," said president Michael Horodniceanu at an Aug. 23 press briefing.

"When you drill vertically, the energy that is created should go laterally," he said. "In this case, it went vertically and actually aimed directly to the  southeast corner of the 72^nd Street deck. The decking lifted and allowed rock to actually spread into the street." He added that the cover was supposed to absorb all of the pressure, but it did not.

The barrier plate that was to contain the blast was 1500 lb, Horodniceanu said. "I believe that it was not anchored down at the edge. This is a question we are asking now," he said.

The team had conducted 72 blasts previously without problems, he noted.

A call to the contractor was not immediately returned.