NEW YORK (CBSNewYork/AP) — Steel plates covering the Second Avenue subway construction site failed to withstand the impact of a controlled blast that sent rocks flying into the street and damaged nearby buildings, the city’s transit authority said Wednesday.

Construction workers were blasting through rock to create an escalator for the Second Avenue subway when two 1,800-pound steel plates were lifted into the air, allowing debris to rain onto the street.

The cover was supposed to absorb the pressure but didn’t, said Michael Horodniceanu, president of capital construction for the Metropolitan Transportation Authority.

The plates were not properly secured to the ground when the blast occurred, Horodniceanu said at a press conference. He said there was also a problem with how some holes were drilled at the site.

“The holes that were drilled in rock outcrop that was blasted were diagonal,” Horodniceanu said. “Normally, we’ll do it in a vertical fashion.”

Blasting at the site will not resume until the private contractor, SK Contractors, provides a new standard operating procedure for conducting it.

“We are taking our time. We’re not hurrying to jump to conclusions,” Horodniceanu said. “We want to make sure that whatever we are evaluating is appropriate.”

Transit officials said they believe the steel covering was not built to withstand the force of an explosion that aimed debris at one section of the plates.

No one was injured during the botched blast, but the agency said it is also extending the frozen zone to keep pedestrians farther from future blasting.

“We pledge to them that we’ll do our best for something like this not to occur again,” said Horodniceanu.

A vacate order was issued as a precaution for the ground floor of one building that had several windows blown out. There was no structural damage to surrounding buildings.

The transit authority is hiring an independent safety consultant to review conditions at the site.

A blast consultant, who had been overseeing the controlled explosions, will be on site when construction resumes and will take a more active role in the process. The no-walk zone for pedestrians will be expanded for safety reasons, officials said.

Workers had already performed 72 successful blasts at the site prior to Tuesday’s accident. The project is slated to be finished in December 2016.

(TM and Copyright 2012 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2012 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

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