TERRE HAUTE, Ind. (AP) — A mishap during a high school chemistry experiment that injured four western Indiana students, leaving one hospitalized, is being investigated by the State Fire Marshal’s office.

Two investigators with the Indiana Department of Homeland Security visited North Central High School in Terre Haute on Wednesday to help investigate Tuesday’s accident, said David Hosick, a spokesman for the state agency.

Hosick told the Tribune-Star the incident involving an unspecified chemistry experiment may have involved “some sort of explosion.”

The school’s principal, Nancy Liston, said one student who suffered burns to his face and an arm remained hospitalized Wednesday. She said three other students were treated and later released at a local hospital for minor cuts and burns and were back in school Wednesday.

Liston said the students were conducting an Advanced Placement course chemistry experiment outside the school that involved fire when “something went wrong.”

The student who remained hospitalized Wednesday served as the “igniter” of the experiment, which Liston said had been conducted many times in the past, including Monday, with no incidents.

Liston said the school, and the district’s insurance, were investigating the cause of the accident.