New York City's transit authority says steel plates covering a subway construction site failed to withstand the impact of a controlled blast that sent rocks flying into the street and damaged nearby buildings this week.

Construction workers were blasting through rock to create an escalator for Manhattan's planned Second Avenue subway line Tuesday when two 1,800-pound steel plates were lifted into the air, raining debris onto the street.

Metropolitan Transportation Authority capital construction president Michael Horodniceanu (ohr-rohd-nee-chee-AN'-oh) says the cover was supposed to absorb the pressure but didn't. He said Wednesday the plates weren't properly secured to the ground.

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

No one was injured during the botched blast. There was no structural damage to surrounding buildings.