Series of mistakes led to fatal Kansas plant explosion in October
The MGPI facility produces distilled spirits and specialty wheat proteins and starches. The chemical release occurred when sulfuric acid was inadvertently unloaded from a tanker truck into a fixed sodium hypochlorite tank at the plant. The two materials combined to produce chlorine gas that sent over 140 individuals, both workers and members of the public, to area hospitals and resulted in shelter-in-place and evacuation orders for thousands of local residents.
The CSB’s investigation found that at about 7:35 am, a tanker truck from Harcros Chemicals arrived at the MGPI facility to deliver sulfuric acid. There, a facility operator escorted the driver to a locked loading area. The operator unlocked the gate to the fill lines and also unlocked the sulfuric acid fill line.
The CSB found that the facility operator likely did not notice that the sodium hypochlorite fill line was also already unlocked before returning to his work station. The driver connected the sulfuric acid discharge hose from the truck into the sodium hypochlorite fill line. The line used to transfer sulfuric acid looked similar to the sodium hypochlorite line, and the two lines were located in close proximity.
As a result of the incorrect connection, thousands of gallons of sulfuric acid from the tanker truck entered the facility’s sodium hypochlorite tank. The resulting mixture created a dense green cloud, which traveled northeast of the facility until the wind shifted the cloud northwest towards a more densely populated area of town. The CSB investigation concluded that emergency shutdown mechanisms were not in place or were not actuated from either a remote location at the facility or in the truck. The CSB found a number of design deficiencies that increased the likelihood of an incorrect connection, such as the close proximity of the fill lines, and unclear and poorly placed chemical labels.
In addition, the CSB found that both MGPI and Harcros did not follow internal procedures for unloading operations. CSB Investigator-in-Charge Lucy Tyler said, “Unloading activities occur at thousands of facilities across the country every day. This event should serve to remind industry to review their own chemical unloading operations and work with motor carriers to ensure chemicals are unloaded safely.”
The CSB has confirmed that the vessel that launched into the Faultless Linen building was a vertical condensate storage tank, technically referred to as the SCR or semi-closed receiver. The SCR provided the condensate or hot water to a steam generation and supply system supporting a corrugated box manufacturing process. That process was being started up on the morning of the incident. Initial visual examination suggests that the bottom pressure boundary of the SCR failed. Once the SCR unit is removed from the building, CSB investigators will conduct a more thorough inspection of the SCR.
According to initial calculations performed by CSB investigators, the SCR contained about 510 gallons of water and was operated at about 330°F and 100 psig. The SCR itself is roughly 20 to 25 feet tall and about 3 feet in diameter and about 3000 lbs. When the vessel failed, the hot condensate jetted from the bottom, converting from hot water to steam. The power of the jet of water rapidly turning to steam broke the vessel loose from its piping attachments and fastenings, propelling it through the internal structure and roof of the building. The downward force of the steam launched the 3,000 pound vessel with a speed of about 120 mph, about 425 feet into the air and about 515 feet from its starting point. The SCR remained airborne for over 10 seconds.
The structural integrity of both buildings is still being assessed. One crew was able to enter an area deemed safe at the Loy-Lange facility to 3-D photo-document the scene. This information will be used to further assess the site and determine next steps to stabilize the building and the location of potential evidence.
Protocols to remove the SCR from the Faultless building are also being developed. The failure mode of the SCR is unknown at this early stage in the assessment, however, in cases of vessel failure it is typical for the CSB to examine issues of vessel operation, preventive maintenance, and mechanical integrity.