On Oct. 21, 2016, a chemical company driver unintentionally attached a sulfuric acid hose to a tank filled with sodium hypochlorite, more commonly known as bleach.
The dangerous solution generated from the chemical reaction mixup at a MGPI Processing Inc. facility released a toxic vapor cloud.
Thousands of Atchison, Kansas residents had to seek shelter, and community members in nearby areas had to evacuate. At least 140 employees and members of the public sought medical attention, according to the U.S. Chemical Safety and Hazard Investigation Board (CSB). An MGPI worker and five members of the public required hospitalization as a result of exposure to the plume.
The CSB determined the only way to stop the dangerous chemical mixing was to close the manual valves or trigger the truck’s emergency shut-offs, which could not be accomplished because of the spreading vapor. The agency also discovered the sulfuric acid and sodium hypochlorite fill lines were similar in resemblance and operation, which made it more likely for a worker to incorrectly connect them.
After a subsequent investigation, the CSB provided the following recommendations to MGPI Processing:
Commission an independent engineering evaluation of the Mod B building and ventilation system and, based on the results of that evaluation, implement design changes and controls to protect occupants from a chemical release. At a minimum, the evaluation should assess the effectiveness of the building ventilation system, indoor and outdoor sources of chemicals, air intake locations, contaminant control methods such as filtration and removal, contaminant monitoring devices, and automation. The engineering evaluation of the ventilation system should consider airborne contaminants during normal operations as well as spills, releases, and chemicals produced from unintended reactions and inadvertent mixing.
Conduct an evaluation of the Mod B chemical transfer equipment (e.g., fill lines, transfer valves, transfer piping, tanks and other associated equipment) and install appropriate engineering safeguards to prevent and mitigate an unintended reaction, chemical release, or spill during bulk unloading. Where feasible, install safeguards, such as alarms and interlocks, to prevent personnel from opening the incorrect chemical transfer valves during deliveries. In addition, install mitigation measures to automatically shut down the transfer of chemicals into the facility based on process deviations or abnormal conditions (e.g., 44 CSB MGPI Processing Case Study pressure, temperature, flow or level indications; gas detection).
Prior to the incident case study release, MGPI Processing began to examine its processes and equipment to “identify opportunities to reduce risk and prevent reoccurrence,” according to the CSB.
The company provided the agency with a list of revisions to the agency, which resulted in only two issued recommendations. It took MGPI only 90 days to comply with the CSB.
Several new safeguards were implemented, including:
- Upgrading chemical unloading and transfer
equipment with chemical portal separation, signage,
unique locks, and fittings
- Implementing an innovative key control and
chemical unloading sequences;
- Upgrading monitoring and detection equipment to
decrease the risk of chemical releases;
- Adding new emergency shutdown devices to
complement the devices that were already in place
- Adding an egress from the facility control room
- Installing more emergency supplied air packs along
the egress path
- Improving movement within the control room by
moving the center control console from the middle
of the control room to the walls
- Conducting several process hazard analyses (PHAs)
covering propylene oxide, phosphorus oxychloride,
and acetic anhydride
- Removing the acetic anhydride process entirely,
leaving only four liquid bulk chemicals at the facility
as opposed to five, thus reducing the number of bulk
flammable chemicals from two to only one.
The CSB commended MGPI Processing, noting it as one of the "fastest full implementations of substantial safety recommendations in the history of the CSB."