CSB Publishes Report on Investigation of Anhydrous Ammonia Release in Virginia
An overpressure in a vessel caused the release of approximately 275 pounds of anhydrous ammonia at a food processing facility in Sterling, Virginia, on July 31, 2024, according to a final report released in late September by the U.S. Chemical Safety and Hazard Investigation Board (CSB). The Cuisine Solutions Sterling plant produces cooked, packaged food products, which necessitates an industrial-scale refrigeration process. Ammonia is used as the refrigerant in this process to chill water used in food preparation and to maintain refrigeration and freezer temperatures for food storage. CSB’s report states that “a refrigeration process upset likely began in one of the heat exchange processes, ultimately leading to overpressure in a vessel” and the discharge of ammonia from an emergency pressure relief valve. Scenarios modeled by CSB indicate that ammonia concentrations at ground level following the release were likely immediately dangerous to life or health (IDLH), or 300 ppm or greater. Exposure to ammonia below the IDLH value may cause headaches, nausea, vomiting, coughing, wheezing, and irritation of the nose, mouth, and throat.
Many workers inhaled ammonia vapor as they evacuated the facility, and emergency responders found more than 10 people unconscious when they arrived at the plant. CSB’s report states that 33 workers were transported to hospitals for treatment and four were admitted, including one who was placed in intensive care. The company estimated the property damage and production losses to be $3 million.
Factors that CSB says contributed to the severity of the incident include insufficient emergency preparedness, ineffective drills for ammonia releases, and a lack of effective emergency shutdown. For example, the plant lacked an automated emergency refrigeration system shutdown, which the agency says could have minimized liquid or aerosol in the ammonia release. In this case, CSB notes that the ammonia cloud “contained a significant liquid component, which caused much of it to rapidly drop to ground level.” The emergency pressure relief valve also opened near the employee parking lot and the building rather than a safe location, the agency found.
“During the release, the facility’s ammonia detection system did not trigger any alarms, no evacuation signal was sounded, and no one at the facility initiated an emergency shutdown of the equipment that was causing the ammonia release,” a CSB news release explains. “The lack of an organized emergency response allowed the situation to escalate and caused more workers to be exposed before reaching safety.”
The report outlines several recommendations for both Cuisine Solutions and the International Institute of All-Natural Refrigeration (IIAR), which has issued ammonia refrigeration standards referred to as “Recognized and Generally Accepted Good Engineering Practice” or RAGAGEP by agencies like OSHA and EPA. CSB urges Cuisine Solutions to improve its emergency action plan and to implement and maintain engineering controls to prevent or mitigate the consequences of similar chemical incidents in the future. The agency calls on IIAR to update its industry guidance for “preventing or mitigating liquid or two-phase atmospheric discharges from emergency pressure relief systems” and to update its Standard for Design of Safe Closed-Circuit Ammonia Refrigeration Systems, ANSI/IIAR 2, “to include a requirement to assess whether emergency pressure relief devices discharge to a safe location, such as with a dispersion analysis.”
More information can be found in CSB’s final report (PDF) and on the agency’s investigation page for the incident.