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Designing pressure relief systems (PRDs) and managing reactive hazards in industrial vessels containing ethylene oxide that may be inadvertently contaminated with water require rigorous technical data. In a 2001 paper published in Process Safety Progress on behalf of AIChE, Melhem et al. established the fourth-order kinetic framework as the benchmark for modeling ethylene oxide contamination by neutral water across industrially relevant concentrations. Developed with contributions from the Ethylene Oxide Industry Council, Shell Chemical, and Union Carbide, this foundational work integrated chemical kinetics, heats of reaction, stoichiometry, physical property data, vapor-liquid equilibrium (VLE), and pressure relief sizing to address historical vessel failures.

The original paper by Melhem et al. (2001) included two significant incidents involving water-contaminated ethylene oxide, including rapid escalation from relief-valve flow to vessel rupture. These incidents provide key lessons for managing ethylene oxide reactive hazards.

The first event, a reactor explosion in Tarragona, Spain, on January 14, 2020, resulted in three fatalities and numerous injuries due to a runaway thermal reaction that led to catastrophic vessel overpressurization.

The second incident, which occurred on September 13, 2002, involved the catastrophic rupture of a railroad tank car in Freeport, Texas, containing a hazardous ethylene oxide-water mixture. This event resulted in the facility's destruction, minor injuries, and a community shelter-in-place order.

In this newsletter, Enio Kumpinsky, Ph.D., presents important updates on ethylene oxide reaction kinetics, process safety, and pressure relief design. In 2024, Levin et al. published peer-reviewed research extending this framework to sulfuric acid-contaminated ethylene oxide, with quantitative kinetic models for scenarios involving cross-contamination by acidic water or scrubber liquor. Topics include:

• Historical Lessons Learned
• Neutral EO/Water and EO/Glycol Kinetics — Still Applicable
• Acid-Catalyzed EO/Water Reaction — Major Literature Update
• Instrumentation & Measurement Capabilities
• Analytical Characterization — An Opportunity for Further Improvement
• Updated Process-Safety Interpretation
• Recommended Updated Experimental Program

By understanding the limits of adiabatic calorimetry instrumentation, accounting for severe catalytic rate accelerations at reduced pH levels, and applying rigorous experimental and dynamic simulation workflows, senior EHS professionals and engineering decision-makers can accurately size pressure relief devices and protect plant integrity.

Have a great and safe day.

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