An explosion that killed one employee and severely injured eight others occurred because the employer failed to follow the hierarchy of controls, according to a federal investigation.
The April 8, 2021 explosion at the Yenkin-Majestic resin plant was caused by the release of flammable solvent vapor through the seal of a closed manway of a kettle that wasn’t constructed to a design pressure appropriate for the process.
1 worker killed, 1 with leg amputated, 7 others injured
A mixture of flammable naphtha solvent vapors and resin liquid became pressurized and then released through the seal of the closed manway, causing a vapor cloud to spread inside and outside of the building that housed the kettle.
Two minutes after the leak began, at 12:04 a.m., the vapor cloud found an ignition source, causing the explosion. The explosion ignited additional flammable material, which led to a large fire that took 11 hours to extinguish. More than 100 firefighters and hazmat team members responded.
Wendell Light, a worker at the plant, was killed from thermal injuries and inhalation of products of combustion, according to a report by the U.S. Chemical Safety and Hazard Investigation Board (CSB). Light was found partially covered by rubble inside the second floor of the resin plant.
Eight other employees were transported to the hospital for injuries ranging from third-degree burns and limb fractures to a leg amputation for an employee who had been crushed under collapsed debris.
Local news outlets reported that the explosion shook nearby homes and was seen, heard, or felt throughout parts of nearby Columbus, Ohio.
Firefighting water runoff contaminated a nearby creek through a storm drain resulting in offsite environmental impacts that lasted for several days.
Total property damage was more than $90 million leading the company to demolish the plant in the aftermath of the incident.
Agitator shut down while operator was out of the room
The incident began during the night shift on April 8, 2021 toward the end of an operating sequence for a kettle known as Kettle 3, which had been progressing normally. Twenty-one employees were onsite at the time, with 12 employees in the resin plant where Kettle 3 was housed, five in the adjacent paint plant and three maintenance technicians supporting both plants.
An employee, labeled Employee A in the CSB report, was overseeing the Kettle 3 batch operation. At 10:19 p.m., he left the kettle room to review sample results at the laboratory. While he was gone, the Kettle 3 agitator unexpectedly shut down at 10:22 p.m. When Employee A arrived back at the kettle room a few minutes later, he didn’t realize that the agitator had shut down as there were no active alarms to notify of a process abnormality.
At 10:33 p.m., the batch temperature in Kettle 3 was about 455 degrees Fahrenheit. Employee A pushed the “Batch Done” button to begin cooling the kettle’s contents, still unaware that the agitator wasn’t running like it should have been.
Pressure builds, vapor releases after agitator was turned on again
Employee A began adding solvent into the kettle at 11:06 p.m., with 300 gallons of the chemical flowing into the kettle at a steady rate over about 26 minutes until about 11:32 p.m. The batch temperature inside the kettle was 430 degrees with the solvent temperature at about 70 degrees. At this point, Employee A waited for Kettle 3’s temperature to cool down to less than 325 degrees.
About 90 minutes after he pushed the “Batch Done” button, Employee A found that the kettle temperature was 424 degrees, which was about 100 degree higher than he expected after the cooling time. He began investigating and noticed for the first time that the agitator wasn’t running. He turned it back on at 12:02 a.m.
The solvent and hot resin hadn’t been mixing while the agitator was off, having remained mostly separated. When the agitator began mixing the kettle’s stagnant layers again, the liquid solvent began vaporizing which caused an increase in pressure inside the kettle.
Pressure continued to increase even after the kettle’s high-pressure alarm and safety interlock were triggered. Eventually, Kettle 3’s closed manway could no longer contain the pressure and released a mixture of hot resin liquid and flammable solvent vapor.
Injured employee, co-worker escape 30 seconds before explosion
In seconds, the entire room was filled with white vapor that obscured visibility. Employee A was sprayed by the material and later told investigators he could smell the solvent, a type of naphtha, inside the room. He attempted to turn off the agitator but couldn’t see through the vapor and had difficulty breathing. Since he couldn’t see or breathe properly, he evacuated the room about 20 seconds after the initial release.
Another employee, Employee B, was in a room nearby and saw Employee A screaming in pain and helped him evacuate from the building. They managed to escape about 30 seconds before the explosion.
Pressure continued to build inside Kettle 3 as more solvent vapor leaked from the sealing around the manway, but Kettle 3 didn’t burst. The pressure eventually began to come back down.
The cloud of flammable solvent vapors was recorded on surveillance cameras moving into adjacent areas of the plant and spilling outside to ground level. Gas detectors inside the plant were triggered and automatically shut down furnaces, but none of them were configured to sound audible alarms. That meant many employees inside or near the plant weren’t aware of the dangerous situation.
The flammable vapor cloud reached an ignition source and exploded at 12:04 a.m.
Properly configured interlocks, alarms weren’t in use
CSB investigators found that Yenkin-Majestic failed to properly use the hierarchy of controls to keep its workers safe.
Keep in mind that the hierarchy of controls “is a risk management principle based on ranking hazard control from most effective to least effective,” as safety professionals know.
In this case, the system design allowed an operator, Employee A, to add solvent to the kettle while the agitator was off. It was the subsequent activation of the agitator that caused the solvent to vaporize rapidly as it contacted the hot resin, leading to the increase in pressure and eventual release of the vapor cloud through the manway.
Yenkin-Majestic didn’t have properly installed or configured interlocks to prevent solvent from being added to the kettle when the agitator was off. Instead, the company relied on computer panel status indicators that had no alarms to communicate agitator status to the kettle operator.
“Although administrative controls are essential for reducing risk, they depend on human actions, perception, and judgment,” the CSB said in the report. “Administrative controls should not be relied on alone, without additional robust design and engineering controls in highly hazardous chemical processes.”
This contributed to both the cause and severity of the explosion.
Hierarchy of controls used along with prevention through design
To prevent this type of incident from happening again, the CSB recommended use of prevention through design principles via the hierarchy of controls in all future resin plant designs.
Specifically, the CSB said Yenkin-Majestic and other chemical companies should “prioritize inherently safer design and engineering controls to prevent process safety events.” This could include:
- documentation of conceptual designs
- safety reviews, hazard analysis and risk assessments of detailed project designs, and
- a plan to address the recommendations to control the hazards.
The CSB also recommended that all equipment that could release flammable materials should be identified and documented. Additionally, Lower Explosive Limit (LEL) detectors should be installed and detection of hazardous conditions should automatically trigger visual and audible alarms to alert plant personnel.
Employees should then be trained on what actions to take, such as prompt evacuation, when these alarms are activated.
