A water heater exploded in a school cafeteria Friday, critically injuring one worker and sending at least 13 students and a faculty member to a hospital.

Students were standing in line to be served in the cafeteria when the explosion occurred, said Richie Brewer (search), assistant principal at Cornersville High School.

A maintenance worker was inspecting a gas water heater in the kitchen when it exploded and knocked the worker through the door, Brewer said.

"He was able to get up and picked up a fire extinguisher and put out what fire there was," Brewer said. "It was a bad thing to happen, but luckily there weren't a lot people in the way of it."

The maintenance worker was in critical condition in the burn center at Vanderbilt University Medical Center, spokesman Jerry Jones said.

At least 13 students and one faculty member have been treated at Marshall Medical Center in Lewisburg, said spokeswoman Phyllis Brown. Other walk-in clinics were reporting treating students for minor injuries.

Brewer said a cafeteria superintendent was cut by a falling light fixture, and a student was hit by a falling piece of ceiling.

Other students reported ringing ears and eye irritation, said Bob Hopkins, spokesman for Tennessee Emergency Management Agency.

The school has about 450 students in grades 7-12.