CSB report: Mixing incompatible materials led to chemical emergency
Posted January 8, 2018
A newly released U.S. Chemical Safety Board (CSB) case study titled “Key Lessons for Preventing Inadvertent Mixing During Chemical Unloading Operations” examines a 2016 chemical release that occurred in a Kansas processing plant. The report identifies 11 major safety issues, including the design of chemical transfer equipment, automated and remote shut-off systems, and chemical unloading procedures. The CSB also provides solutions to prevent mixing incidents at similar facilities across the country.
The processing plant produces distilled spirits and specialty wheat proteins and starches. The chemical release in 2016 occurred when sulfuric acid was inadvertently unloaded from a tanker truck into a fixed sodium hypochlorite tank at the plant. The materials combined to produce chlorine gas and other by-products that sent more than 140 people, both workers and members of the community, to area hospitals. Thousands of local residents were forced to evacuate their homes and others were told to shelter-in-place.
Events leading to the emergency
The Board’s investigation found that a series of events led to the emergency. On the morning of the incident, a tanker truck arrived at the processing plant to deliver sulfuric acid. A plant employee escorted the driver to the loading dock and unlocked the gate to the fill lines and the sulfuric acid fill line. However, the operator was unaware that the sodium hypochlorite fill line was also unlocked. Further, the two lines were only 18 inches apart, looked similar, and were not clearly marked. The driver inadvertently connected his truck’s sulfuric acid hose to the sodium hypochlorite line.
The incorrect connection meant thousands of gallons of sulfuric acid from the tanker truck entered the facility’s sodium hypochlorite tank – creating a dense green cloud of toxic gas that traveled in the wind toward a densely populated area of the community.
The CSB’s findings affirm the need for facilities to pay close attention to the design and operation of chemical transfer equipment. In addition to evaluating their chemical unloading equipment and processes, facilities should implement safeguards to reduce the likelihood of an incident, while considering human factors that could impact how facility operators and drivers interact with equipment.
The CSB instructs facility management to evaluate their chemical transfer equipment and processes and, where feasible, install alarms and interlocks in the process control system that can shut down the transfer of chemicals in an emergency.
Recommendations focus on unloading procedures, planning, and training
The report offers safety recommendations to the companies involved in the incident as well as the county’s department of emergency management. The recommendations focus on proper guidance regarding unloading procedures, planning, and employee training as well as for emergency responders. The case study also highlights an existing recommendation for ventilation guidance for control buildings.
Along with the case study, the Board produced a safety video detailing the events leading to the release and features interviews by the CSB’s lead investigator and Chairperson Vanessa A. Sullivan. Find the report and video at www.csb.gov.
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