A manufacturer’s drive to restart a process pushes people past their breaking point. Mistakes combine to cause disaster.
History has shown that industrial disasters are rarely the result of some single failure in a plant environment that is otherwise carefully operated and scrupulously maintained. In most situations, an incident, large or small, is the logical and inevitable result of a long series of compromises allowing deterioration of people and equipment. The question, “Why did this happen?” could be replaced with “Why didn’t this happen sooner?” Such was the case at Bayer Crop Science’s plant at Institute, West Virginia, August 28, 2008.
A scary historical context
While the actual events were different, the 2008 incident carried many echoes of the 1984 disaster in Bhopal, India, when MIC (methylisocyanate) gas was released from a Union Carbide pesticide plant, resulting in about 3000 immediate fatalities with thousands more suffering permanent and partial disabilities. The Institute and Bhopal plants were similar (both produced carbamate agricultural pesticides), and MIC was produced and stored at both locations. Union Carbide also owned the Institute plant from 1947 until it sold the facility to Rhone-Poulenc in 1986 with the rest of its agricultural division. Rhone-Poulenc and its successors owned the site until Bayer Crop Science acquired it in 2002.
In 2008, the Institute plant was the only facility in the U.S. that produced, stored and used significant amounts of MIC, potentially as much as 6700 gallons on the site at a time. Following the Bhopal disaster, the similarities of these two plants on opposite sides of the world were not lost on the surrounding community and U.S. safety regulators. For the larger Charleston, West Virginia, area, living with toxic chemicals has been part of its history. There are many industrial chemical processing facilities in the Kanawha river valley, and safety planning efforts through the area date back to the 1950s. Nonetheless, after Bhopal, the presence of so much MIC was a particular concern, causing Union Carbide (once it finally admitted there was MIC at the plant) and subsequent owners to take additional efforts to prevent releases.
August 28, 2008
While we will pull apart the specific circumstances in greater detail in subsequent posts, the Institute incident began, as incidents often do, during a restart after an outage. As production in the methomyl unit was ramping up, operators noticed that pressure was building in a newly installed residue treater vessel on the south side of the unit.
Two employees went to investigate expecting to find that the vent pipe was blocked only to be present when it violently ruptured, ejecting 2200 gallons of flammable solvents and toxic insecticide residue around the immediate area. Estimates after the fact suggested it exploded with the force of 17 pounds of TNT. One of the two employees was killed instantly, the other died of burns 41 days later. The resulting fire continued for more than four hours.
The MIC tank, approximately 70 feet from the treater, was hit by flying debris but undamaged. Thermal shielding protected it from the fire. (MIC must be stored below 40 ºC to prevent a highly exothermic self-polymerization reaction and it is normally refrigerated. At the Institute site, it was typically kept below 0 ºC.) Fortunately, there was no release of MIC during the incident.
Why did it explode? The residue treater was designed to decompose residual uncrystallized methomyl by mixing it with heated methyl isobutyl ketone (MIBK) solvent. MIBK was supposed to be put into the vessel first and heated to a critical temperature. Once this was reached, methomyl-contaminated solvent from the process (known as “flasher bottoms”) could be added where it would decompose safely, allowing the remaining solvent to be burned in one of the facility boilers. The night of the disaster, the reactor had not been filled with MIBK, but methomyl-containing flasher bottoms from the process were pumped in anyway. Without MIBK to control the exothermic reaction, it began to escalate and generate high levels of gas in the vessel. The venting system was overwhelmed, and the vessel exploded.