Environmental Forensic Investigation of an Accidental Ethylene Oxide Release, Acute Air Dispersion Modeling, and Community Exposure Assessment
Project Overview
Accidental chemical releases present some of the most technically challenging investigations in environmental forensic science because they require reconstructing rapidly changing release conditions, evaluating atmospheric transport over short time periods, estimating community exposure, and interpreting potential health impacts using limited historical data. Unlike routine industrial emissions, accidental releases frequently involve large quantities of hazardous chemicals discharged over minutes or hours under dynamic process conditions. Evaluating these events requires integrating chemical engineering, process safety, atmospheric science, industrial hygiene, meteorology, environmental chemistry, toxicology, air dispersion modeling, and quantitative exposure assessment to reconstruct the incident and estimate potential impacts to surrounding communities (National Research Council, 2010; U.S. EPA, 2017).
RoseyFields conducted a comprehensive environmental forensic investigation involving an accidental release of ethylene oxide (EtO) following a major industrial process incident at a large chemical manufacturing facility. The objectives of the investigation were to reconstruct the source term associated with the accidental release, evaluate multiple potential release-duration scenarios, estimate airborne EtO concentrations using accepted atmospheric dispersion modeling techniques, characterize potential acute community exposures, and evaluate these exposures relative to established health-based guidance values. The investigation integrated engineering analyses, process safety evaluations, historical operational records, atmospheric dispersion modeling, meteorological analyses, toxicological criteria, and geographic information systems (GIS) to develop a scientifically defensible reconstruction of the release and resulting community exposure.
A principal component of the investigation involved reconstructing the accidental source term from available engineering information and regulatory documentation. Because the total quantity of material released was known but the exact release duration could not be determined with certainty, multiple scientifically reasonable release scenarios were developed. These scenarios evaluated releases occurring over durations ranging from several seconds to approximately one hour, resulting in substantially different average emission rates and atmospheric concentration predictions. Evaluating multiple source-term scenarios allowed the investigation to characterize uncertainty while providing bounding estimates of potential acute exposure rather than relying upon a single assumed release duration. This sensitivity analysis strengthened the technical defensibility of the overall exposure assessment and provided a more comprehensive understanding of the incident.
Atmospheric transport was evaluated using accepted regulatory and emergency response dispersion modeling techniques to estimate airborne EtO concentrations under representative meteorological conditions during the release. Engineering evaluations incorporated release characteristics, source configuration, meteorological observations, terrain, and atmospheric stability to estimate the transport and dilution of the chemical plume across surrounding areas. Model predictions were subsequently compared with acute health-based exposure criteria to evaluate potential community impacts under multiple release scenarios. Integrating process engineering, source-term reconstruction, atmospheric science, toxicology, and quantitative exposure assessment produced a comprehensive environmental forensic investigation capable of supporting environmental consulting, emergency response evaluations, regulatory investigations, and expert witness services while maintaining complete confidentiality regarding the underlying project (U.S. EPA, 2017; National Research Council, 2010).
Chemicals of Concern
The primary chemical evaluated during this environmental forensic investigation was ethylene oxide (EtO), a highly reactive, colorless gas widely used as an industrial intermediate in the manufacture of numerous commercial chemicals. EtO is also produced and handled in large quantities throughout the chemical manufacturing industry because of its versatility in producing glycols, surfactants, solvents, and specialty chemical products. Due to its flammability, reactivity, and recognized toxicity, accidental releases of EtO present unique engineering, environmental, and public health challenges requiring rapid scientific evaluation to characterize potential community exposures and assess associated health risks (U.S. EPA, 2016; ATSDR, 1990).
Unlike routine industrial emissions that typically occur at relatively constant rates over extended periods, accidental releases often involve large quantities of material discharged over very short durations. Consequently, airborne concentrations during accidental releases are controlled primarily by the release rate, release duration, atmospheric stability, wind speed, wind direction, source geometry, and chemical properties of the released material. Small differences in any of these parameters can significantly influence predicted downwind concentrations, making accurate source-term reconstruction one of the most important components of an environmental forensic investigation (U.S. EPA, 2017; National Research Council, 2010).
A major component of this investigation involved evaluating multiple plausible release-duration scenarios to account for uncertainty regarding the timing of the accidental discharge. Although the total quantity of EtO released could be estimated from engineering records and process inventories, the exact release duration was less certain because emergency response activities, process isolation, equipment conditions, and operational changes evolved throughout the incident. Rather than relying upon a single assumed release duration, multiple release scenarios were developed representing rapid releases occurring over seconds as well as more prolonged releases occurring over several minutes and longer durations. Evaluating this range of potential release conditions allowed the investigation to establish scientifically defensible upper- and lower-bound estimates of airborne concentrations while reducing uncertainty associated with the source-term reconstruction (National Research Council, 2010; CCPS, 2019).
The investigation also considered the influence of combustion and chemical transformation on potential community exposure. Depending upon the conditions present during an accidental industrial fire or explosion, a portion of the released EtO may combust, while another portion may be emitted directly into the atmosphere. Because combustion efficiency can vary substantially during dynamic emergency events, sensitivity analyses were performed to evaluate a range of potential combustion assumptions. These engineering evaluations provided additional insight into how different release mechanisms could influence predicted airborne concentrations and downwind exposure estimates. Incorporating multiple scientifically reasonable scenarios strengthened the overall environmental forensic evaluation by explicitly accounting for uncertainties associated with emergency response conditions and evolving process operations (AIChE Center for Chemical Process Safety, 2019; U.S. EPA, 2017).
Acute exposure assessment relied upon comparison of modeled air concentrations with established health-based exposure criteria developed specifically for short-duration chemical releases. Acute Exposure Guideline Levels (AEGLs), Emergency Response Planning Guidelines (ERPGs), and other toxicological benchmarks provide concentration thresholds for evaluating the potential for discomfort, irreversible health effects, or life-threatening impacts over specified exposure durations. Comparing modeled concentrations with these scientifically accepted criteria allowed the investigation to evaluate potential public health implications under multiple release scenarios while providing emergency planning information relevant to evacuation decisions, shelter-in-place recommendations, and post-incident exposure assessments. Integrating chemical engineering, atmospheric science, toxicology, industrial hygiene, meteorology, and quantitative exposure assessment produced a comprehensive environmental forensic evaluation capable of supporting emergency response analysis, regulatory investigations, environmental consulting, and expert witness services involving accidental hazardous chemical releases (National Research Council, 2010; AIHA, 2020).
Methods
A comprehensive environmental forensic investigation was conducted to reconstruct an accidental ethylene oxide (EtO) release following a major industrial process upset and to estimate potential acute community exposures using established engineering, atmospheric science, industrial hygiene, toxicology, and environmental modeling methodologies. Because accidental releases differ fundamentally from routine industrial emissions, the investigation focused on reconstructing the timing, magnitude, duration, and physical characteristics of the release while accounting for uncertainties associated with emergency response activities and rapidly changing process conditions. Multiple independent datasets were integrated using a weight-of-evidence approach to produce a scientifically defensible evaluation of the incident and its potential environmental impacts (ASTM International, 2021; U.S. EPA, 2017).
The investigation began with a detailed engineering review of available incident information, including process descriptions, equipment configurations, operational records, emergency response documentation, regulatory reports, and publicly available technical investigations. These materials were evaluated to reconstruct the sequence of events leading to the release, identify the likely release location, estimate the quantity of EtO discharged, and characterize the physical mechanisms governing the release. Particular attention was given to understanding equipment failures, process pressures, emergency shutdown procedures, and containment measures that influenced both the magnitude and duration of the release. This engineering reconstruction established the foundation for subsequent atmospheric dispersion modeling and exposure assessment (Center for Chemical Process Safety, 2019; U.S. Chemical Safety and Hazard Investigation Board, 2024).
Because the precise duration of the release could not be determined with complete certainty, multiple source-term scenarios were developed to evaluate a range of scientifically plausible release rates. Each scenario assumed the same total mass released while varying the discharge duration from very short, high-rate releases to longer-duration, lower-rate releases. This sensitivity analysis allowed investigators to evaluate the influence of release duration on predicted airborne concentrations while explicitly accounting for uncertainty associated with emergency response actions, process isolation, and continuing equipment depressurization. Developing multiple bounding scenarios is consistent with accepted environmental forensic practice and provides a more technically robust assessment than relying upon a single assumed release condition (National Research Council, 2010; ASTM International, 2021).
Atmospheric transport and dispersion were evaluated using regulatory-quality air dispersion modeling consistent with current U.S. Environmental Protection Agency guidance. Engineering source parameters, release characteristics, terrain, building influences, and representative meteorological observations were incorporated into the modeling analyses to estimate short-term airborne EtO concentrations throughout surrounding communities. Meteorological evaluations included wind direction, wind speed, atmospheric stability, temperature, and mixing height during the release period because each of these variables significantly influences plume movement and dilution. Geographic information systems (GIS) were subsequently used to visualize modeled concentration patterns and identify areas potentially experiencing the greatest short-term exposure (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
Modeled concentrations were evaluated using established acute toxicological criteria, including Acute Exposure Guideline Levels (AEGLs) and other recognized emergency exposure benchmarks developed for short-duration chemical releases. Exposure estimates were calculated for multiple averaging periods corresponding to accepted toxicological guidance values. Comparing modeled concentrations with these health-based criteria allowed the investigation to evaluate the potential for adverse health effects under multiple release scenarios while providing a scientifically objective framework for interpreting emergency response actions such as shelter-in-place recommendations and precautionary evacuations. Integrating chemical engineering, process safety, atmospheric dispersion modeling, meteorology, toxicology, exposure science, and quantitative risk assessment produced a comprehensive environmental forensic investigation suitable for environmental consulting, emergency response evaluations, regulatory investigations, and expert witness services involving accidental hazardous chemical releases (AIHA, 2020; National Research Council, 2010).
Results
The environmental forensic investigation demonstrated that the estimated airborne concentrations of ethylene oxide (EtO) were highly dependent upon the assumed release duration, emphasizing the importance of accurately reconstructing source-term characteristics during accidental chemical releases. Sensitivity analyses showed that shorter-duration releases produced substantially higher peak airborne concentrations near the release point, while longer-duration releases resulted in lower maximum concentrations distributed over a broader geographic area. Although each modeling scenario assumed the same total quantity of EtO released, the variation in release duration significantly influenced predicted community exposures and the extent of the affected area. Evaluating multiple scientifically plausible source terms therefore provided a more comprehensive understanding of potential exposure conditions while appropriately accounting for uncertainty associated with the incident reconstruction (National Research Council, 2010; U.S. EPA, 2017).
Atmospheric dispersion modeling demonstrated that meteorological conditions during the incident strongly influenced plume movement and downwind concentrations. Wind direction, atmospheric stability, wind speed, and mixing height collectively governed the transport and dilution of the EtO plume throughout the surrounding area. Model results indicated that relatively small changes in meteorological conditions could alter both the location and magnitude of predicted peak concentrations, highlighting the importance of incorporating representative site-specific weather observations into emergency response modeling. Geographic information system analyses illustrated the spatial distribution of modeled concentrations and identified the areas most likely to experience elevated short-term airborne exposures under each modeled scenario (American Meteorological Society & U.S. EPA, 2019; World Meteorological Organization, 2018).
Comparison of modeled concentrations with established acute exposure criteria demonstrated that predicted health impacts varied considerably depending upon the assumed release scenario and exposure duration. The highest modeled concentrations occurred near the source immediately following the release, with concentrations decreasing rapidly as atmospheric dispersion diluted the plume. Toxicological evaluations were performed using nationally recognized acute exposure benchmarks to characterize the potential for transient irritation, more significant health effects, and emergency response considerations. Rather than relying upon a single exposure estimate, evaluating multiple release scenarios provided a scientifically defensible range of potential outcomes and allowed emergency planning assumptions to be assessed using accepted toxicological guidance (National Research Council, 2010; AIHA, 2020).
The investigation further demonstrated the value of integrating engineering analyses with atmospheric dispersion modeling when reconstructing accidental releases. Process engineering evaluations provided essential information regarding equipment configuration, release mechanisms, emergency shutdown procedures, and source-term development that could not be inferred from air modeling alone. Conversely, atmospheric modeling translated engineering estimates into predicted environmental concentrations and community exposure estimates. The combination of these complementary disciplines significantly reduced uncertainty associated with the overall investigation while strengthening confidence in the reconstructed release scenario and exposure assessment (Center for Chemical Process Safety, 2019; ASTM International, 2021).
Overall, the investigation demonstrated that combining process safety engineering, incident reconstruction, atmospheric dispersion modeling, meteorological analysis, toxicology, industrial hygiene, geographic information systems, and quantitative exposure assessment provides a scientifically rigorous framework for evaluating accidental hazardous chemical releases. This multidisciplinary approach allows investigators to characterize potential community exposure, evaluate emergency response actions, quantify uncertainty through sensitivity analyses, and provide technically defensible scientific opinions suitable for environmental consulting, regulatory investigations, emergency response evaluations, remediation planning, and expert witness services. By integrating multiple independent scientific disciplines rather than relying upon any single analytical method, environmental forensic investigations can provide objective and evidence-based assessments of complex accidental release events (ASTM International, 2021; U.S. EPA, 2017).
Conclusions
This environmental forensic investigation demonstrated that evaluating accidental releases of hazardous airborne chemicals requires the integration of process engineering, atmospheric science, environmental chemistry, industrial hygiene, toxicology, meteorology, air dispersion modeling, and quantitative exposure assessment. Unlike routine industrial emissions, accidental releases occur under rapidly evolving conditions that often involve uncertain release durations, changing process parameters, emergency response actions, and complex atmospheric transport. Consequently, reconstructing these events requires multiple independent lines of scientific evidence rather than reliance upon a single dataset or analytical technique. The multidisciplinary approach employed in this investigation provided a scientifically rigorous framework for evaluating potential community exposure while appropriately characterizing uncertainty associated with the release reconstruction (ASTM International, 2021; U.S. EPA, 2017).
The investigation demonstrated that accurate source-term reconstruction is one of the most critical components of accidental release modeling. Engineering evaluations showed that assumptions regarding release duration, discharge rate, process conditions, equipment performance, and emergency mitigation measures substantially influenced predicted airborne concentrations. By developing multiple scientifically plausible release scenarios rather than relying upon a single deterministic assumption, the investigation established a range of potential exposure estimates that better represented the uncertainties inherent in emergency incidents. This approach strengthens the scientific defensibility of environmental forensic evaluations and provides a more comprehensive understanding of potential public health impacts (Center for Chemical Process Safety, 2019; National Research Council, 2010).
The investigation further demonstrated the importance of combining atmospheric dispersion modeling with detailed meteorological analyses and toxicological evaluation. Wind direction, atmospheric stability, wind speed, terrain, and mixing conditions significantly influenced the movement and dilution of the airborne plume following the release. Comparing modeled concentrations with nationally recognized acute exposure criteria provided an objective scientific basis for evaluating potential health impacts and assessing the appropriateness of emergency response actions. Integrating engineering analyses, atmospheric modeling, meteorology, and toxicology allowed exposure estimates to be interpreted within an accepted public health framework while reducing uncertainty associated with individual analytical methods (American Meteorological Society & U.S. EPA, 2019; AIHA, 2020).
This case study illustrates the important role of environmental forensic science in reconstructing accidental industrial releases and evaluating potential community exposure following chemical emergencies. By integrating incident reconstruction, process safety engineering, source-term development, atmospheric dispersion modeling, meteorological analysis, environmental chemistry, toxicology, industrial hygiene, geographic information systems, and quantitative exposure assessment, RoseyFields provides scientifically rigorous evaluations capable of supporting emergency response analyses, regulatory investigations, environmental consulting, remediation planning, and expert witness services. These multidisciplinary investigations produce objective, evidence-based scientific analyses that improve understanding of accidental chemical releases, airborne contaminant transport, and potential human exposure while remaining consistent with accepted engineering practice, current environmental science, and established regulatory guidance (ASTM International, 2021; U.S. EPA, 2017).
This investigation was conducted under the direction of Dr. Paul Rosenfeld, an environmental scientist and environmental forensic expert with extensive experience in accidental chemical release investigations, source-term reconstruction, air dispersion modeling, exposure assessment, and human health risk evaluation. Dr. Rosenfeld’s work focuses on complex environmental contamination matters involving accidental releases of hazardous air pollutants, process upsets, industrial fires and explosions, emergency response evaluations, atmospheric transport of toxic gases, acute community exposure assessment, and the reconstruction of short-duration release events affecting nearby residential and commercial receptors. His expertise includes developing and evaluating release scenarios through the integration of process safety engineering, industrial operations, meteorology, environmental chemistry, toxicology, industrial hygiene, geographic information systems (GIS), and quantitative exposure modeling to determine whether accidental industrial releases and emergency response conditions are consistent with observed environmental conditions and potential human health impacts. Through RoseyFields LLC, Dr. Rosenfeld provides environmental forensic analysis, environmental due diligence, regulatory and compliance support, emergency response evaluation, toxic tort and personal injury case assessment, and expert witness testimony involving ethylene oxide releases, accidental hazardous chemical emissions, acute inhalation exposure, source attribution, and short- and long-term environmental and human health risks associated with industrial process incidents.
References
Agency for Toxic Substances and Disease Registry. (1990). Toxicological profile for ethylene oxide. U.S. Department of Health and Human Services.
American Industrial Hygiene Association. (2020). Emergency Response Planning Guidelines (ERPGs): Ethylene Oxide. AIHA.
American Meteorological Society, & U.S. Environmental Protection Agency. (2019). AERMOD: Description of Model Formulation. U.S. Environmental Protection Agency.
ASTM International. (2021). Standard guide for environmental forensic investigations. ASTM International.
Center for Chemical Process Safety. (2019). Guidelines for consequence analysis of chemical releases (2nd ed.). American Institute of Chemical Engineers.
International Agency for Research on Cancer. (2012). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100F: Chemical Agents and Related Occupations. International Agency for Research on Cancer.
National Research Council. (2010). Acute Exposure Guideline Levels for Selected Airborne Chemicals, Volume 9. National Academies Press.
U.S. Chemical Safety and Hazard Investigation Board. (2024). Investigation Report: Explosions, Fires, and Toxic Ethylene Oxide Release at an Industrial Chemical Manufacturing Facility. U.S. Chemical Safety and Hazard Investigation Board.
U.S. Environmental Protection Agency. (2016). Evaluation of the Inhalation Carcinogenicity of Ethylene Oxide (Final Report). U.S. Environmental Protection Agency.
U.S. Environmental Protection Agency. (2017). Guideline on Air Quality Models (40 CFR Part 51, Appendix W). U.S. Environmental Protection Agency.
World Meteorological Organization. (2018). Guide to Meteorological Instruments and Methods of Observation (WMO-No. 8). World Meteorological Organization.
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