A liquid nitrogen leak at a northeast Georgia poultry plant killed six people Thursday and hospitalized 11 others in an incident officials called “devastating” and a “tragedy.”

At least three of those injured at the Foundation Food Group plant in Gainesville were reported in critical condition.

Poultry plants rely on refrigeration systems that can include liquid nitrogen. Firefighters, the U.S. Occupational Safety and Health Administration and the state fire marshal were investigating the cause of the leak.

“I would definitely ask everyone to keep the families in your prayers,” Hall County Sheriff Gerald Couch said during a press conference. “A lot of these folks that came into work today didn’t have any idea of what would happen, nor did their families. They’re not in a profession that you would expect something like this to happen, but here we are.”

He added: “It’ll take quite some time to determine the cause.”

Foundation Food Group Vice President for Human Resources Nicholas Ancrum called the leak a tragic accident and said early indications are that a nitrogen line ruptured in the facility.

The plant was known as Prime Pak Foods until January, when it merged into Foundation Food Group, a company that takes raw chicken and processes it into products like chicken fingers and individual chicken cuts for restaurants and food service operations.

“Those lost today include maintenance, supervisory and management team members,” Ancrum said in a statement. “Every team member is equally important to us and our hearts go out to their families and communities who have suffered such a devastating loss.”

Ancrum added 130 employees were evacuated from the plant and Foundation Food Group is cooperating with the investigation into the leak.

When leaked into the air, liquid nitrogen vaporizes into an odorless gas that’s capable of displacing oxygen. That means leaks in enclosed spaces can become deadly by pushing away breathable air, according to the U.S. Chemical Safety Board.

Workers who had fled the plant were gathered outside when firefighters responded to the leak Thursday morning, Hall County Fire Department Division Chief Zach Brackett said.

“Once the units arrived, they found a large contingent of employees that had evacuated, along with multiple victims that were in that crowd that were also experiencing medical emergencies around the facility,” Brackett told reporters in a televised news briefing.