The US Chemical Safety and Hazard Investigation Board (CSB) announced that it is sending investigators to the Prime Pak Foods plant in Gainesville, GA after six workers died in an incident Thursday.

“According to initial reports, a release of liquid nitrogen led to six fatalities, nine others were transported to the hospital, with three in critical condition and six in fair condition,” the CSB said in a release.

Two CBS investigators are expected to arrive at the scene late Thursday. Two other team members and the agency’s chairman and chief executive officer are slated to arrive on Friday.

Crews were sent to the facility at about 10 a.m. after receiving word that someone had suffered burns, Powder & Bulk Solids reported in an earlier article, citing information form NBC News. HAZMAT personnel were also dispatched just after the incident was called in.

“It was a leak of unknown cause that has occurred in the system here,” Hall County Fire Department Division Chief Zach Brackett told the Associated Press (AP). “We still have a lot of information we’re trying to gather from the scene.”

The US Department of Labor’s Occupational Safety and Health Administration (OSHA) has also reportedly opened an investigation into the deaths.