PESTICIDE WASTE TANK EXPLOSION — METHOMYL — 2 FATALITIES
Bayer CropScience Pesticide Waste Tank Explosion
Bayer CropScience LP
📍 Institute, WV
Incident: August 28, 2008  •  CSB Report: January 2011
2
Fatalities
Methomyl (Carbamate Pesticide) / Residue Blow Tank Contents — Runaway Decomposition
Chemical Involved
10
CSB Recommendations
📋 Incident Summary

On August 28, 2008, an explosion and fire at the Bayer CropScience facility in Institute, West Virginia, killed two workers and injured eight others. The explosion originated in a residue treater — a waste processing unit that treated pesticide waste, including methomyl residues, with steam.

The CSB investigation found that methomyl, a carbamate insecticide, is thermally unstable and can undergo runaway decomposition at elevated temperatures. On the night of the incident, a large quantity of methomyl-containing waste was present in the residue treater when it was heated, triggering a runaway decomposition that generated toxic gases, raised pressure beyond the vessel's capacity, and caused the explosion.

Bayer CropScience had not conducted an adequate reactive hazard assessment for the residue treater that accounted for the composition and thermal stability of the waste materials it processed. The company was also operating the unit outside of its design specifications.

🔎 Key Findings
Finding 01
Methomyl Thermally Unstable — Runaway Decomposition in Residue Treater
Methomyl, a carbamate insecticide, decomposes exothermically at elevated temperatures. A large quantity of methomyl-containing waste in the heated residue treater triggered a runaway decomposition, generating toxic gases and catastrophic pressure.
Finding 02
Reactive Hazard of Methomyl Waste Not Assessed for Residue Treater
Bayer CropScience had not conducted an adequate reactive hazard assessment for the residue treater that accounted for the thermally unstable properties of methomyl-containing waste materials processed in the unit.
Finding 03
Residue Treater Operated Outside Design Specifications
The unit was operating with quantities and compositions of waste materials that exceeded or deviated from the design basis of the residue treater. These deviations were not formally analyzed through MOC or PHA.
Finding 04
Two Workers Killed in Explosion — Eight Injured
Two employees of Bayer CropScience were killed in the explosion. Eight additional workers were injured. The Institute facility is located near a residential area, and the incident caused community concern about toxic material releases.
Finding 05
Community Near Former Union Carbide Bhopal-Era Facility
The Institute facility was the former Union Carbide plant associated with MIC (methyl isocyanate) production — the same chemical responsible for the Bhopal disaster. The community around Institute has heightened process safety awareness given this history.
🔍 Root Causes
1
Thermal Stability of Methomyl Waste Not Characterized for Residue Treater Operation
The runaway decomposition was directly caused by the failure to characterize the thermal stability of methomyl-containing waste at the temperatures applied in the residue treater. This reactive hazard was foreseeable with adequate calorimetric testing.
2
Waste Composition and Quantity Deviations Not Reviewed Through MOC or PHA
The operation of the residue treater with waste streams outside its original design basis was not subjected to MOC or PHA review. Changes in the waste composition that increased reactive hazard were not formally evaluated.
3
No Emergency Relief Sized for Runaway Decomposition Scenario
Pressure relief systems for the residue treater were not sized for the gas generation rate of a methomyl runaway decomposition, leaving the vessel without adequate protection against the actual hazard scenario.
☑ CSB Recommendations
→ Bayer CropScience / Pesticide and Agrochemical Manufacturers
Conduct reactive hazard assessment including calorimetric testing for all waste processing units; characterize the thermal stability of all waste streams processed in heated units; size pressure relief for worst-case reactive scenario.
→ Chemical Industry
Apply MOC review whenever waste stream compositions or quantities in waste processing units deviate from the original design basis; include waste processing units in PHA programs as process equipment.
→ OSHA
Review and enforce PSM coverage for waste treatment and residue processing operations at chemical manufacturing facilities; ensure these units are included in facility PSM programs, not treated as auxiliary or non-process equipment.
→ EPA
Review Risk Management Program (RMP) requirements for residue and waste processing operations at facilities handling pesticides and other reactive chemicals; consider whether waste processing units should require worst-case scenario analysis under RMP.
💡 Lessons Learned
Waste processing and residue treatment units at chemical manufacturing facilities are not auxiliary equipment — they are process equipment, and they require the same process hazard analysis, reactive hazard assessment, and mechanical integrity attention as primary production equipment. The residue treater at Bayer CropScience processed chemically reactive waste materials at elevated temperatures: this is exactly the process condition profile that requires formal reactive hazard assessment.
Thermal stability of waste streams must be specifically characterized for the temperatures used in waste processing. A waste stream containing reactive or thermally unstable compounds does not become safe simply because it is being treated as waste rather than as a process chemical. Calorimetric testing of representative waste samples at the processing temperatures is a standard, affordable test that provides the information needed to assess runaway reaction potential.
Management of change must apply to changes in what goes into a process unit — not just changes to the unit itself. When the composition, quantity, or properties of the material processed in a unit change, that is a change in the process, and it must be reviewed through MOC and reflected in the applicable PHA. If a waste stream adds a thermally unstable component to a heated unit, that is a MOC-relevant process change.
The history of a facility location matters for community risk perception and emergency planning. The Institute facility's history as a former Union Carbide site with community awareness of toxic chemical hazards underscores the importance of proactive process safety management — not because of the history, but because that history means the community's trust depends entirely on demonstrated, not assumed, process safety performance.
PHA: Process Hazard AnalysisSOP: Operating ProceduresMI: Mechanical IntegrityMOC: Management of Change
🔨 Safety Meeting Toolbox Talk
►Have you conducted a reactive hazard assessment — including calorimetric testing — for all heated waste processing, residue treatment, or neutralization units at your facility? Does the assessment address all waste stream compositions that are or could be processed in each unit?
►Does your MOC program require review when the composition or quantity of material processed in a waste treatment or residue processing unit changes from the original design basis?
►Are your waste processing units included in your facility PHA program as process equipment? When were these units last included in a PHA or hazard review?
►Are pressure relief systems on heated waste processing vessels sized for a reactive/decomposition runaway scenario, or only for normal operating pressure upsets?
Immediate Action Items
✓Identify all heated waste processing, residue treatment, and neutralization units at your facility; verify that reactive hazard assessments including calorimetric testing have been conducted for all waste streams they process.
✓Review MOC records for waste processing units; identify any changes in waste stream composition or quantity that were not processed through MOC review and conduct retroactive hazard analysis.
✓Include all waste processing and residue treatment units in your next PHA revalidation cycle as first-class process equipment nodes.
✓Verify that pressure relief systems on heated waste processing vessels are adequately sized for worst-case reactive decomposition scenarios.
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 4 PSM elements (PHA · SOP · MI · MOC). Each represents a documented gap that process safety documentation and consulting can close before a similar event occurs at your facility.

Process Hazard Analysis (PHA)
A structured PHA or HAZOP study exists to identify exactly these scenarios before they occur. When PHA is absent, superficial, or overdue for revalidation, hazards operate unseen until they kill someone.
Supporting documents in our library →
Operating Procedures (SOPs)
Operators cannot reliably hold safe operating limits without clear, current, enforced procedures. Deviation from acceptable operating conditions — a root cause here — is a direct consequence of SOP failure.
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Mechanical Integrity (MI)
Equipment must be designed, inspected, and maintained to operate safely in its intended service. Mechanical integrity failures — degraded equipment, missed inspections, deferred repairs — contributed to loss of containment here.
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Management of Change (MOC)
Changes to equipment, chemistry, operating limits, or procedures that bypass formal review create new hazard pathways your PHA never evaluated. MOC failures open the door to incidents like this one.
Supporting documents in our library →
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