Six South Carolina high school students were scalded while riding a school bus when steam from a faulty radiator was released inside the vehicle.

The State reports that the six injured boys are members of the soccer team at White Knoll High School in Lexington, S.C. The bus was taking team members to a soccer match Tuesday afternoon in Lugoff, S.C.

Lexington County School District One says in a news release that one of its buses experienced a mechanical problem Tuesday afternoon while traveling on Interstate Hwy. 20.

The coolant supply hose for the heater core ruptured, and that caused a mixture of steam, hot water, and coolant mixture to be released inside the bus and burn the students.

The injured—one 12th grader, two 11th graders and three 10th graders—received medical treatment, and some of those students were back in school Wednesday morning.

The bus had passed an inspection within the last 12 months, the district says. Officials are trying to determine what caused the radiator hose to fail.