Four students were taken to the hospital and a building was cordoned off after an explosion in a boiler room at a Santa Ana high school early Tuesday.
Officials said that about 7:30 a.m. a pipe above a boiler at Valley High School at 1801 S. Greenville St. exploded and sent chunks of the building's roof and wall flying through the air.
Images of the aftermath on TV showed sections of wall and ceiling ripped to shreds. A door was thrown about 75 feet from the blast, said Orange County Fire Authority Capt. Jon Muir.
The explosion was either the result of a mechanical malfunction or a pocket of natural gas in a pipe that ignited, Muir said.
Four students who were sitting on a bench near the building suffered minor injuries and were taken to the hospital, Muir said.
The students complained of aches and pains and were generally shaken up, he said. Three other students were hurt but not taken to the hospital.
Classes were not in session at the time.
The blast caused structural damage to the building and access has been blocked. School business continued as normal on the rest of the campus, a school official said.
The cause of the blast remains under investigation.
Video courtesy of Valley High, Santa Ana.