At a press conference yesterday to discuss the cause of the out-of-control Second Avenue subway explosion that showered an Upper East Side intersection with debris, the MTA had some explaining to do. An independent investigation is currently underway to determine exactly how Tuesday's planned explosion went so horribly wrong, but officials are focusing on a pair of 1,800 pound steel plates that were not strong enough to handle the force of the blast. Also, freakin' contractors, ya know?

"What happened was completely unacceptable and should not have occurred,” Michael Horodniceanu, president of MTA Capital Construction, told reporters. "I’m not jumping on or blaming anyone, but the responsibility lies with the contractor." That would be SSK, a company that was "placed on the city’s caution list after revealing that it had received several federal Occupational Safety and Health Administration violations in the past five years that resulted in penalties,"according to the Post.

The actual physics of the accident appear to be this: If a hole is drilled vertically, the explosion goes out to the sides, if it's drilled horizontally, the blast energy goes upwards. On Tuesday, workers had drilled a hole at a 30 degree angle, and, as WNYC explains it, that "was enough of a horizontal that the force of the blast went to one spot that was only covered by steel plates." Yesterday a source said workers had "covered the wrong hole."

“The force of the blast was concentrated in one area. And the deck above was not able to withstand that force because it was not anchored in,” says MTA spokesman Kevin Ortiz. Blasting at the site has been halted pending the outcome of the investigation.