GOSHEN — State investigators will investigate an explosion at a northern Indiana fertilizer plant that injured four people, including two who are in critical condition at a Fort Wayne hospital.

Indiana Occupational Safety and Health Administration spokeswoman Chetrice Mosley says investigators were headed Tuesday to T & T Fertilizer southwest of Goshen to investigate the accident.

Authorities say four workers of T & T Fertilizer and Southwest Welding in Goshen were injured when a tank exploded during welding Monday.

St. Joseph Hospital spokeswoman Shelly Lybarger said 24-year-old Adrian Martin of Goshen was in critical condition Tuesday. Sixteen-year-old Anthony Rodes, also of Goshen, was in serious condition. A person answering the telephone at Southwest Welding identified them as employees.

Dean Myers, 61, of Goshen, was treated at a hospital and released, according to the Elkhart County Sheriff’s Department. Ricky Schrock, 56, of Constantine, Mich., was listed in serious condition Tuesday in St. Joseph Hospital, Fort Wayne.

There was no answer at T & T Fertilizer on Tuesday.

Authorities said the explosion caused about 2,000 gallons of ammonia to leak from the tank. Rob Elstro, a spokesman for the Indiana Department of Environmental Management, said most of the leaked ammonia was contained by a concrete pad and wall that surrounds the tank where the leak occurred. He said some ammonia spilled over the side onto surrounding gravel. That gravel was scraped up and put on another concrete slab and was being cleaned Tuesday, he said.

The runoff from that was put into T & T application trucks and being applied to nearby farmland “to help with some local farmers,” Elstro said.

A review of OSHA records showed that neither T & T Fertilizer nor Southwest Welding had any safety violations over the past five years. Neither had notified IOSHA about the accident within eight hours of the accident as required by law, Mosley said. IOSHA was notified of the accident by IDEM, she said. She said the potential fine for failing to report an accident depends on the findings of the investigation.

She said the department had not been notified that one of the injured was a 16-year-old. But she said in any accident in which someone under age 18 is hurt, the state Department of Labor’s Child Labor Division investigates.