It happens every day. Chemicals end up delivered and unloaded at facilities across the globe, and even though unloading operations are simple, the consequences of a miscommunication or oversight can have a severe impact workers and surrounding communities.
That is exactly what happened at the MGPI Processing Inc. plant in Atchison, Kansas, on October, 2016.
That is when a potentially deadly mixture of two chemicals, sulfuric acid and sodium hypochlorite, produced a cloud containing chlorine and other compounds. The ensuing cloud affected workers onsite and members of the public in the surrounding community, according to a report from the U.S. Chemical Safety Board (CSB). The incident occurred during a routine chemical delivery of sulfuric acid from a Harcros Chemicals (Harcros) cargo tank motor vehicle (CTMV) at the MGPI facility tank farm.
About 140 people ended up going to hospitals because of the cloud, which also forced residents to remain indoors or temporarily evacuate the city.
It all started at 7:35 a.m. October 21, 2016, as a Harcros CTMV arrived at the MGPI Atchison facility to complete a delivery of 30 percent sulfuric acid. Upon arrival, the Harcros driver exited the cab and began to pressurize the cargo tank for unloading. At 7:42 a.m., the driver took the bills of lading to the Mod B building where the MGPI night shift operator on duty reviewed and signed the paperwork for accepting a delivery. Because the driver arrived at MGPI at 7:35 a.m., prior to the start of dayshift, the night shift operator accepted the delivery.
At 7:44 a.m., the operator escorted the driver from the Mod B building to the chemical unloading area. When they reached the rear of the CTMV, the driver set his paperwork on the back of the cargo tank and walked down the passenger side to finish donning his personal protective equipment (PPE). During this time, the operator unlocked the gate in front of the transfer equipment and removed the lock on the cam lever dust cap for the sulfuric acid fill line. The operator placed the lock from the sulfuric acid fill line on the angle iron above the fill line. The driver removed the seal from the back of the cargo tank, handed it to the operator, and then retrieved the hose from the CTMV to begin the connections.
The operator reported he pointed out the location of the sulfuric acid fill line to the driver and the driver acknowledged the location; the driver, however, reported the operator did not point out the fill line.
The operator then returned to the Mod B building at approximately 7:47 a.m. before he saw the driver connect the discharge hose to the fill line. The driver removed the dust cap from the first unlocked fill line that he saw at the facility, which he assumed to be the sulfuric acid fill line. The driver connected the hose to the fill line and then connected the hose to the truck. The driver checked the air pressure in the cargo tank, checked for leaks and upon not finding any, opened the facility’s valve and the valve on the cargo tank to begin discharging sulfuric acid. The driver returned to his cab, checked his air pressure on the way, climbed inside, and set his paperwork down. During this time, the MGPI day shift operator and a trainee were in the Mod B building discussing plant operating status with the night shift operator.
Shortly before 8:00 a.m., a greenish-yellow gas began emitting from the sodium hypochlorite bulk tank, forming a cloud. The cloud grew, covering the Harcros truck and the Mod B building, and then migrated offsite in a northeast direction.
The three operators inside the Mod B control room at the time of the release quickly became aware of the reaction by the odd smell of gas that entered the building. They immediately attempted to access their emergency escape respirator face pieces, but were unable to do so because the respirator face pieces were not stored in a readily accessible location or had been moved. As a result, all three operators were forced to evacuate the building without respiratory protection. After exiting, operators ran northeast through the cloud until they reached fresh air near the railroad tracks. At the railroad tracks, one of the operators used his radio to alert MGPI employees of the emergency. Following this alert, another company employee contacted 911 at 7:59 a.m.
Driver Flees Scene
The driver, who was in the cab of the truck, first noticed the gas cloud in his rearview mirror. He tried to get to the connection area at the rear of the truck by running down the driver side, but the gas overwhelmed him. The driver turned around and attempted the same from the passenger side but again was overwhelmed by the gas. At this point, the manager of the facility’s adjacent waste water treatment plant (WWTP) saw the release and shouted for the driver to run in his direction. The WWTP manager brought the driver inside the WWTP control room, gave him water, and radioed MGPI employees the driver was inside and out of the cloud. The WWTP manager also alerted MGPI management of the release by phone and radio.
Although the sulfuric acid dust cap was unlocked immediately prior to unloading, the CSB found the sodium hypochlorite fill line was also accessible to the driver.
The driver connected the sulfuric acid discharge hose to the unsecured fill line for the sodium hypochlorite bulk tank, which resulted in the inadvertent mixing of approximately 4,000 gallons of sulfuric acid and 5,850 gallons of sodium hypochlorite. This mixture of incompatible materials resulted in a reaction that promoted the release of a cloud containing chlorine gas and other compounds.
The CSB’s investigation examines key issues that include the design of chemical transfer equipment, automated and remote shutoff systems and chemical unloading procedures.
The CSB’s report covered 11 key lessons stemming from the chemical release and outlines improvements that can end up implemented at similar facilities across the nation. The recommendations focus on proper guidance regarding unloading procedures, planning and training.
The board also said facility management should evaluate 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.
The CSB’s report issued safety recommendations to the companies involved in the incident, as well as the Atchison County, Kansas, emergency management department. A CSB case study reasserts a previous recommendation for ventilation guidance for control buildings.
“Our findings re-affirms the need for facilities to pay careful attention to the design and operation of chemical transfer equipment to prevent similar events,” said Vanessa Sutherland, CSB chairperson. “Industry needs to review their own safety practices to ensure that such every delivery is executed safely.”
Lead investigator Lucy Tyler said companies must work in collaboration with their chemical distributors to conduct a risk assessment toward helping define responsibilities.
New Measures Implemented
MGPI released a statement concerning the board’s case study.
“We have found the CSB’s efforts to be helpful in supporting our own internal initiatives to ensure a safe environment,” the company said.
Company officials said MGPI already has implemented new measures that include changes to its chemical unloading process.
“Additionally, we engaged Burns & McDonnell to provide a comprehensive review of our unloading and chemical storage methods to further strengthen the safety of our systems and engineering controls and help prevent the recurrence of any such incident in the future,” the statement added.