Three workers were injured, one critically, on Thursday when a gas explosion damaged at least three floors of New York City’s John F. Kennedy High School, WLNY-TV reports.

According to The New York Times, seven people were working on the school’s sixth floor when a gas line exploded just after 8:00 p.m., blowing out windows and rattling nearby buildings. From the NY Daily News:

“It was a thunder, a really loud explosion,” said Addae Hicks, 21, a custodial worker on the school’s sixth floor.

The gas line exploded after a contractor hit it with a blowtorch, Hicks said.

“Honestly, I thought it was a bomb,” said Jason Osorio, a custodial worker who dashed out of the rumbling building. “I’m happy to be alive.”

Nearly 140 firefighters and paramedics reportedly responded to the explosion.

[Image via WNBC]