Hazardous Ammonia Release in Virginia: CSB Final Report

The US Chemical Safety and Hazard Investigation Board (CSB) issued its final report following an investigation of an incident that occurred July 31, 2024, at a metal treatment facility in Sterling, Virginia.

On that day, a toxic cloud of ammonia was released that injured dozens of workers.

What Caused the Ammonia Release?

A malfunction in the ammonia refrigeration system caused an overpressure event at about 8:20 PM on July 31, 2024. An emergency pressure relief valve activated in response to the overpressure event and discharged about 275 pounds of anhydrous ammonia into the atmosphere. The release produced a toxic ammonia cloud that settled at ground level due to its density.

Key Lessons for Industry

Measure and Store Process Data

Companies should ensure that they measure and store process data so that when an incident or process upset occurs, they can analyze the data, determine the causes, and make changes to stop the upset or prevent another incident. The inability to access such process data can mask serious process control problems. Employees cannot respond to a process upset or prevent future ones if they cannot see how a process upset developed. Investigating an incident without sufficient process data hampers investigation and makes a repeat incident more likely to occur.

Do Not Approach Without Proper PPE

While a dispersion analysis does not relate the visible cloud to the toxic cloud, the analysis, when paired with a video of the visible cloud, clearly shows that much of a toxic ammonia cloud can also be invisible. DO NOT approach an ammonia cloud without proper personal protective equipment (PPE). 

Ensure Safe Discharge and Evacuation

Building wake effects and other complex flow considerations should also be evaluated in dispersion analyses where applicable, to ensure a safe discharge to the atmosphere and safe evacuation where necessary.

For ammonia refrigeration relief systems, the liquid fraction in an aerosol release, discharge velocity, discharge orientation, and discharge elevation are intricately related and should be studied for any atmospheric relief case to ensure that emergency pressure relief valves discharge to the atmosphere safely.

Document Release Scenarios in the Emergency Action Plan

Distinctive alarms or alarms specific to particular release scenarios allow workers to properly respond to a release quickly. Different release scenarios should be documented in the Emergency Action Plan, and may include multiple distinct alarms and responses, such as one for shelter-in-place and one for evacuation.

Train Employees in Emergency Shutdown Procedures

Multiple employees should be trained to perform simple tasks such as using an emergency shutdown device. A well-designed Emergency Action Plan should include simple procedures that backup employees could complete in the event that specialized employees are unavailable or disabled during the emergency. Effective implementation of an Emergency Action Plan should include such items as using the emergency shutdown button if it can be safely accessed, coupled with regular drills to ensure that all personnel onsite clearly understand their duties in an emergency, even if those duties only include safe evacuation.

Fully Implement All Process Safety Management Elements

Companies should ensure that they fully implement all PSM elements and requirements in their programs, and make sure any gaps are addressed.

Automate Emergency Actions Where Possible

Where installed, automated emergency actions can speed the response to a release, thereby minimizing the release quantity and consequences of an ammonia refrigeration system release. 

US CSB News Release
US CSB Final Report