Minnesota's Occupational Safety and Health Administration has opened an investigation into an ammonia leak that was discovered Tuesday at the JBS Swift pork plant in Worthington.
More than 50 workers were hospitalized after an overhead pipe carrying the refrigerant broke. JBS officials were not sure what caused the break.
OSHA inspectors will interview employees who were working at the time, as well as review the company's safety and health procedures and the training that was offered to employees, according to OSHA Communications Director James Honerman.
"We're just looking to see what may have caused or contributed to this, and figure out a solution to ensure it doesn't happen again," Honerman said. "Whenever there's an accident that causes three or more employees to go to the hospital due to one accident, Minnesota OSHA considers that one of its priorities to go and inspect."
There were no serious injuries, and most of the workers have been released following checkups.
Honerman expects the investigation will take a couple months.
It's the second ammonia leak at the plant in the last year and a half. In January 2008, a faulty valve sent 34 employees to the hospital.
OSHA investigated that incident and found two safety violations, for which the company paid a $3,500 penalty.
Honerman said it's still unclear if Tuesday's leak also involved a faulty valve.
"I can't compare the two, but whatever we found last time they certainly addressed," he said.
JBS, one of the world's largest meat processors, is headquartered in Brazil. The Worthington plant employs more than 2,000 workers.
(The Associated Press contributed to this report)