Four workers who were performing maintenance at the Waupaca Plant in Tell City, Indiana were transported to the University of Louisville Hospital’s burn unit on Monday after being injured at the facility.

Officials have released few details about the incident, which occurred at 10:30 a.m. in the company’s cupola, according to news sources.

Three of the Waupaca employees were flown by helicopter and one went by ambulance. All are expected to recover.

Waupaca Foundry produces iron castings, focusing on transportation, construction, agriculture and industrial markets worldwide.

The Perry County Sheriff’s Department, Indiana State Police ad Tell City Police Department coordinated on securing the landing zone and quickly getting the injured workers on their way to treatment.

OSHA is investigating the incident. Waupaca has also indicated that it is conducting an investigation.