Visual depiction of the disaster released from the Chemical Safety and Hazard Investigation Board (CSB) in a new safety video into the deadly January 28, 2021, nitrogen release.
The release occurred when the bubbler tube which measured and controlled the level of liquid nitrogen in an immersion freezer at the facility ended up bent, causing an abnormally large amount of liquid nitrogen to pump into the freezer, which exceeded the freezer’s capacity.
The excess liquid nitrogen overflowed out of the freezer on Line 4 in Plant 4 and then vaporized, forming a deadly vapor cloud inside the poorly ventilated freezer room. Two maintenance workers who were in the room at the time of the release died from asphyxiation, and four additional workers also died from asphyxiation when they entered the freezer room during the incident.
The CSB’s safety video, entitled “Fatal Fog: Liquid Nitrogen Release at Foundation Food Group,” includes an animation of the events leading to the incident.
’Preventable Tragedy’
“This preventable tragedy underscores the importance of safety leadership, systems and training,” said CSB Board Member Sylvia Johnson. “FFG lacked critical monitoring equipment and alarms. Management did not provide workers with adequate training or equipment to respond safely to a liquid nitrogen release. During this incident, several workers tried to save their colleagues lives without realizing that nitrogen had displaced oxygen in parts of the plant. While attempting to rescue their colleagues and evacuate, four workers lost their lives. In total, six workers died in this preventable incident and three workers and a firefighter were seriously injured.”
Five safety issues CSB found in the incident include:
- Single Point of Failure
- Atmospheric Monitoring and Alarm Systems
- Emergency Preparedness
- Process Safety Management System
- Product Stewardship
Single Point of Failure
The immersion freezer design included a device called a bubbler tube, which measured the liquid nitrogen level inside the freezer. The bubbler tube was likely bent during maintenance activity, rendering it unable to measure and control the freezer’s liquid nitrogen level.
One screen from the video shows the bubbler tube which measured and controlled the level of liquid nitrogen in an immersion freezer ended up bent, causing an abnormally large amount of liquid nitrogen to pump into the freezer and overflow into the freezer room.
Source: CSB
As a result, liquid nitrogen overflowed from the freezer and filled the room with vaporized nitrogen. This design was vulnerable to a single point of failure. Once the tube became bent, there was nothing else to prevent the release of liquid nitrogen. The design team did not adequately consider the consequences of the failure of the bubbler tube – a critical safety component. In addition, during fabrication of the immersion freezer, Messer failed to detect a manufacturing defect that exacerbated the potential for the bubbler tube to be bent – a missing clamp meant to secure the bubbler tube to the freezer.
Atmospheric Monitoring and Alarm Systems
There is abundant industry guidance on the importance of atmospheric monitoring when the potential for hazardous atmospheres exists. FFG, however, did not install atmospheric monitoring equipment in the freezer room. There was no equipment installed to detect the oxygen-deficient atmosphere in the freezer room, automatically shut off the liquid nitrogen supply, and notify personnel to evacuate the area.
Emergency Preparedness
FFG did not inform, train, equip, drill, or otherwise prepare its workforce for a release of liquid nitrogen. FFG’s workforce lacked knowledge of the hazards of nitrogen and its ability to create an oxygen-deficient atmosphere, were unable to recognize an oxygen-deficient atmosphere, and lacked any equipment or PPE that would have enabled safe entry into an oxygen- deficient atmosphere.
As a result, after the discovery of the first two deceased workers, four other employees who entered the freezer room also died from asphyxiation due to the released nitrogen during response or rescue attempts.
Process Safety Management System
FFG had no documented process safety management policy, allowed the job position responsible for safety management to be vacant for more than a year prior to the incident, did not evaluate the process hazards associated with the freezer, lacked written procedures and a management of change process, and did not train its workers on the asphyxiation hazards of liquid nitrogen.
Product Stewardship
Messer owned the liquid nitrogen bulk storage tanks and the Line 4 immersion- spiral freezer and leased the equipment to FFG. At the time of the incident, Messer had institutional knowledge, experience, policies, and practices for effective product stewardship but applied those practices only to the bulk storage tanks and not to the Line 4 freezer process. Throughout its relationship with FFG, Messer identified issues with FFG’s safety practices and nonconformance to industry guidance, but despite FFG’s unsafe practices, Messer continued to supply FFG with liquid nitrogen.
A screen shot from the video shows liquid nitrogen overflowing from the freezer creating a vapor cloud inside the poorly ventilated freezer room.
Source: CSB
The incident started off January 28, 2021, when operations on Line 4 started at 7:16 a.m., according to the report. Continuing the trend from the previous days, soft, partially-frozen chicken product came out of the immersion-spiral freezer. As a result, Line 4 stopped processing chicken at 8:14 a.m. so maintenance personnel could troubleshoot the issue. At 8:20 a.m., the Line 4 Packaging Supervisor instructed the Line 4 workers to go on break while maintenance workers attempted to resolve the freezing issue. The maintenance workers conducted the maintenance without shutting down the freezer and with the transition box door and immersion freezer lid safety switches intentionally bypassed.
CSB determined it was likely while the Line 4 workers were on break, the bubbler tube in the immersion freezer somehow became bent, thereby preventing the freezer’s liquid nitrogen level control system from working properly. The liquid nitrogen level then increased in an uncontrolled manner, and liquid nitrogen overflowed from the immersion freezer, filling the freezer room with vaporized nitrogen that displaced the room’s oxygen.
White Cloud Visible
After 20 minutes, at 8:40 a.m., the Line 4 workers returned from break. At this time the workers noticed a cloud of white fog coming from the Line 4 freezer room but took no further action. According to one employee, because workers regularly observed white fog in the freezer room, they did not believe there was a problem. By 9:40 a.m., having not heard from the Line 4 Packaging Supervisor for over an hour, one of the Line 4 workers decided to look for him. The Line 4 worker entered the Line 4 freezer room through an elevated opening.
The Line 4 worker observed a dense white cloud approximately four feet high filling the room. She also saw one of the maintenance workers lying motionless on the ground in front of the conveyor belt. The Line 4 worker exited the freezer room by crawling back through the elevated opening and returned to where the other Line 4 workers were in the RTE area. She informed the other workers of what she saw and then crawled through the elevated opening again, this time with another worker to confirm her observations. The Line 4 workers again returned to the area and then left to locate the Line 1 Packaging Supervisor to inform him about what they had observed.
As the video notes, the CSB found FFG did not have an atmospheric monitoring and alarm system that could have alerted workers to the deadly conditions in the freezer room. FFG also did not have an effective plan for dealing with a hazardous liquid nitrogen release and did not train its employees about how to safely respond to such a release.
Click here to view the video.