A liquid nitrogen leak from a cryogenic freezing system at Foundation Food Group’s Gainesville Plant 4 killed six people, required 12 to be hospitalized, and led to the evacuation of 130 others in Gainesville, Ga. The plant is owned by Foundation Food Group, recently formed by the merger of Prime-Pack Foods and Victory Processing. The U.S. Chemical Safety Board is on site and investigating.

On Thursday, January 28, the poultry processing plant was operating five production lines prior to the liquid nitrogen release. The event occurred on Line 4, where chicken is processed to include seasoning, cooking and flash freezing. CSB investigators are focusing on the cryogenic freezing system based on information from various sources and observations at the scene. The liquid nitrogen-based, cryogenic food freezing system was installed in late 2020 to replace an ammonia refrigeration freezing line.

According to the CSB investigators, some tools were located in the vicinity of the Line 4 immersion freezer, and some unplanned maintenance was being conducted on Line 4 near the time of the release.

“There was a release of liquid nitrogen — an inadvertent release — which rapidly converted to a gas,” said Katherine Lemos, the chairman and CEO of the CSB in press briefing. “The gas is heavier than air and forces oxygen out of the room.”

The spiral freezer includes equipment inside the plant as well as tanks outside. CSB notes that major portions of the liquid nitrogen system, interior and exterior, were installed and commissioned in the last 4 to 6 weeks.

“In a description of the incident with CSB investigators, a maintenance manager described personally closing the isolation valves of the tanks in the parking lot subsequent to the event shutting off the supply to the building, which limited the potential damage or consequence of the event,” Lemos noted. “Plant 4 received two to three 18-wheel truckloads per day of liquid nitrogen.”

During planned operation on Line 4, the liquid nitrogen immersion-spiral freezer flash freezes the chicken in two stages. In the first stage, the chicken travels on a conveyer belt and is submerged in liquid nitrogen at a temperature of -320°F (-195.5°C).  In the second stage, the conveyer belt travels through the spiral freezer portion, and the chicken is exposed to gaseous nitrogen recovered from the first stage to complete the freezing process.

CSB expects their investigation to take some time. “We will be working diligently to determine more information regarding the insulation, the age, operation, phase of operation, maintenance and condition of all equipment related to the liquid nitrogen system, which is internal and external,” Lemos said.

This article has been updated.