LUGOFF, S.C. — Six students were injured when a mechanical issue released steam and hot fluid into their school bus, district officials said.

According to Lexington County School District 1, the incident occurred on Tuesday evening on a 1999 model year bus that was transporting 42 high school soccer players, a student statistician, and two coaches.

The district said in a press release that a “detailed examination of the bus shows that the coolant supply hose for the heater core ruptured. Since the system is pressurized, it caused a steam, hot water, coolant mixture to release inside the bus. That mixture caused the students’ injuries.”

The six students who were injured ranged in age from 15 to 17 years old. Some of them returned to school on Wednesday morning, Lexington District 1 reported.

The transportation office for the local school system, Kershaw County School District, sent a bus to the scene of the incident to transport the uninjured soccer team members to a nearby elementary school. There, another Lexington District 1 bus picked them up to bring them home.

“The safety and well-being of our students is always our first concern, and we are keeping these students and their families in our thoughts,” the Lexington district said on Tuesday. “We are also grateful for the help of the Kershaw County School District.”

The bus that experienced the mechanical issue was a 1999 Thomas Built rear-engine model. According to Lexington District 1, the bus has a current inspection, which means that it was inspected within the past 12 months.

South Carolina has been working to update its state-owned school bus fleet, which is said to be one of the oldest in the nation. About half of the state’s 5,582 school buses are more than 15 years old, such as the 1999 model in the Tuesday incident.

In January, South Carolina Superintendent Molly Spearman asked state legislators to fund school bus replacement as well as driver and technician pay increases.

In February, the South Carolina Department of Education acquired 26 new propane school buses to replace older diesel models.