COLUMBIA, Mo • A blast in a science building on the University of Missouri's flagship campus sent four students to the hospital Monday.

Chancellor Brady Deaton was outside Schweitzer Hall about four hours after a hydrogen explosion there blasted out 17 third-floor windows and sent glass flying 40 feet outside the historic biochemistry hall about 2:20 p.m.

"I'm really concerned about the victims," Deaton said. "We will be working overtime to be sure any condition that led to this will be addressed."

The explosion occurred in a lab on the third floor of the building that has been on the eastern edge of the campus since 1912. Four people - two postdoctoral students, a graduate student and another person - were injured when some of the hydrogen they were working with exploded.

"It looked as if a bomb went off in the lab," said Capt. Eric Hartman of the Columbia Fire Department.

The worst of those injured was originally said to have "life-threatening" injuries by the fire department, but that victim was later upgraded to "good condition." All four victims - who were not identified - were sent to University Hospital in Columbia.

Fire investigators attributed the blast to human error, Hartman said. Someone in the lab turned on the hydrogen supply to a piece of lab equipment but was not familiar with the warning system designed to alert when the hydrogen level got dangerously high. When the gas reached an ignition source, it exploded.

An automated sprinkler system extinguished most of the small fire triggered by the blast; Columbia firefighters put out the rest. Hartman said the building did not appear to sustain any structural damage.

Student Erin Bucko, 21, of Columbia, was one building away. Her class jumped when they heard the explosion and then ran to the windows to see smoke pouring out of Schweitzer Hall. "It was really scary for us," Bucko said. "Automatically, your heart just kind of stops."