Environmental Forensic Investigation of an Industrial Chemical Release Using Air Dispersion Modeling and Exposure Assessment
Project Overview
This environmental forensic investigation evaluated airborne chemical releases resulting from a large-scale industrial chemical incident involving the thermal decomposition and combustion of organic peroxide products following catastrophic flooding. The investigation integrated air dispersion modeling, emissions reconstruction, atmospheric science, environmental chemistry, industrial hygiene, toxicology, exposure assessment, and quantitative human health risk assessment to characterize airborne contaminant releases, evaluate potential exposure pathways, and assess the magnitude and spatial extent of chemical exposures experienced by emergency responders and nearby populations. Multiple independent technical documents, emissions inventories, regulatory reports, meteorological analyses, and engineering evaluations were reviewed to reconstruct the incident and develop a comprehensive scientific assessment of airborne chemical releases.
The investigation focused on the decomposition and combustion of thermally unstable organic peroxide formulations that lost refrigeration during a prolonged flooding event. Because the chemical composition of decomposition products was uncertain, the investigation evaluated reported emissions together with scientifically supported chemical surrogates representing likely combustion products and toxic decomposition byproducts. Airborne contaminants evaluated included organic peroxides, hydrogen peroxide, sulfur dioxide, nitrogen dioxide, ozone, hydrogen fluoride, chlorine, chlorine dioxide, phosgene, acetic acid, volatile organic compounds (VOCs), particulate matter, nonane, and additional combustion products capable of causing acute respiratory irritation and pulmonary injury. The investigation incorporated emissions inventories, Safety Data Sheets (SDSs), published toxicological literature, regulatory guidance, and chemical property information to characterize the potential hazards associated with each release scenario.
A major component of the investigation involved independent evaluation of previously developed air dispersion models together with supplemental atmospheric modeling performed using accepted emergency response methodologies. Existing atmospheric dispersion analyses, emissions estimates, and meteorological inputs were critically reviewed to identify modeling assumptions, uncertainties, and potential limitations. Additional ALOHA modeling, sensitivity analyses, chemical surrogate evaluations, and threat-zone analyses were performed to evaluate alternative release scenarios and estimate airborne contaminant concentrations across multiple locations. Modeled concentrations were compared with reported exposure locations, toxicological benchmarks, acute exposure guideline levels, and health-based screening criteria to assess the likelihood of adverse health effects associated with the incident.
The investigation was conducted using accepted principles of environmental chemistry, atmospheric dispersion modeling, industrial hygiene, environmental toxicology, contaminant fate and transport, emergency response science, and quantitative risk assessment. Rather than relying on a single modeling approach or emissions inventory, the evaluation synthesized engineering analyses, emissions reports, meteorological observations, atmospheric modeling, chemical property data, toxicological information, regulatory guidance, and published scientific literature into a comprehensive weight-of-evidence assessment. This multidisciplinary methodology provides a scientifically robust framework for evaluating complex accidental chemical releases and demonstrates how modern environmental forensic investigations integrate multiple independent technical disciplines to characterize airborne contaminant releases and assess human exposure following major industrial incidents.
Chemicals of Concern
This investigation evaluated a complex mixture of airborne contaminants generated during a large-scale industrial chemical release involving the thermal decomposition and combustion of organic peroxide products. Because elevated temperatures and uncontrolled decomposition produce numerous secondary reaction products, the investigation evaluated both reported emissions and scientifically supported chemical surrogates capable of representing likely decomposition products and combustion byproducts. The principal chemicals of concern included organic peroxides, hydrogen peroxide, sulfur dioxide, nitrogen dioxide, hydrogen fluoride, chlorine, chlorine dioxide, phosgene, ozone, acetic acid, volatile organic compounds (VOCs), particulate matter, nonane, tert-butyl peroxybenzoate, and additional combustion-related byproducts. These contaminants were evaluated using environmental chemistry, toxicology, atmospheric science, industrial hygiene, and quantitative exposure assessment to characterize potential health hazards associated with the chemical release.
Organic peroxides represented the principal source material evaluated during the investigation because they are thermally unstable compounds capable of undergoing rapid exothermic decomposition when refrigeration is lost. Environmental chemistry evaluations examined the physical and chemical behavior of these materials under elevated temperature conditions together with published information describing decomposition mechanisms, combustion characteristics, and expected degradation products. Because complete characterization of decomposition products following uncontrolled combustion is often difficult, scientifically supported surrogate compounds were selected to represent chemicals possessing similar toxicological and physicochemical properties. This approach provided a scientifically defensible framework for evaluating potential airborne exposures under conditions where complete emissions characterization was unavailable.
The investigation also evaluated several combustion gases and highly reactive inorganic compounds known to produce acute respiratory effects following inhalation exposure. These included sulfur dioxide, nitrogen dioxide, hydrogen fluoride, chlorine, chlorine dioxide, and phosgene, each of which possesses well-established toxicological properties capable of producing respiratory irritation, pulmonary inflammation, chemical pneumonitis, or delayed pulmonary injury at sufficiently elevated airborne concentrations. Toxicological evaluations incorporated published Acute Exposure Guideline Levels (AEGLs), Protective Action Criteria (PACs), Safety Data Sheets (SDSs), regulatory guidance, and peer-reviewed toxicological literature to evaluate the severity of potential inhalation hazards associated with each modeled release scenario.
Additional evaluation focused on hydrogen peroxide, acetic acid, ozone, volatile organic compounds, nonane, and tert-butyl peroxybenzoate, which were identified either as reported emissions, decomposition products, or scientifically appropriate chemical surrogates representing the thermal degradation of organic peroxide formulations. Hydrogen peroxide and organic peroxide compounds were evaluated because of their oxidizing properties and potential respiratory toxicity. Acetic acid was evaluated because organic peroxide decomposition may generate acidic decomposition products capable of causing mucous membrane irritation. Ozone and nitrogen oxides were considered because high-temperature combustion processes frequently generate reactive oxidants capable of contributing to acute respiratory symptoms. Volatile organic compounds, nonane, and related hydrocarbons were similarly evaluated because they may contribute to acute inhalation exposure and collectively represent an important component of combustion emissions.
Airborne particulate matter generated during combustion also represented an important component of the exposure evaluation. Combustion of organic materials, trailers, structural components, and associated industrial materials generates fine and respirable particulate matter capable of transporting condensed organic compounds, soot, combustion residues, and adsorbed chemical contaminants. Environmental chemistry and industrial hygiene evaluations therefore considered both gaseous contaminants and particulate emissions when characterizing airborne exposure. Integration of particulate emissions with gaseous chemical releases provided a more comprehensive assessment of inhalation hazards because combustion plumes frequently contain complex mixtures of gases and respirable particles capable of producing additive respiratory effects.
Finally, the investigation recognized that accidental industrial chemical releases rarely involve exposure to a single contaminant. Instead, emergency responders and nearby populations may experience simultaneous exposure to numerous reactive gases, combustion products, particulate matter, volatile organic compounds, and decomposition products generated under rapidly changing atmospheric conditions. Accordingly, this investigation integrated environmental chemistry, atmospheric dispersion modeling, industrial hygiene, toxicology, emergency response science, and quantitative risk assessment to evaluate cumulative airborne exposure rather than isolated contaminants alone. This multidisciplinary approach provides a scientifically reliable framework for characterizing complex industrial chemical releases and assessing potential health impacts associated with large-scale accidental emissions involving reactive chemical mixtures.
Methods
The investigation was conducted using accepted principles of atmospheric dispersion modeling, environmental chemistry, industrial hygiene, emergency response science, contaminant fate and transport, environmental toxicology, and quantitative human health risk assessment. Because the incident involved multiple chemical release mechanisms—including thermal decomposition, uncontrolled combustion, wastewater overflow, and the release of volatile decomposition products—the investigation integrated emissions inventories, engineering evaluations, meteorological observations, regulatory reports, Safety Data Sheets (SDSs), toxicological literature, and atmospheric modeling to reconstruct airborne contaminant releases and evaluate potential human exposure. Rather than relying upon a single emissions inventory or dispersion model, the investigation employed a multidisciplinary weight-of-evidence approach combining engineering analyses, atmospheric science, exposure reconstruction, and toxicology to characterize the magnitude, timing, and geographic extent of the chemical release.
A major component of the investigation involved reconstruction of the individual emission events associated with the incident. Engineering documents, facility records, emissions inventories, and regulatory reports were reviewed to identify the sequence of chemical releases, including wastewater overflows, decomposition of refrigerated organic peroxide products, combustion of temporary storage trailers, controlled burns, and associated releases of combustion products. Reported emission quantities for particulate matter, sulfur dioxide, nitrogen oxides, volatile organic compounds, combustion gases, and individual chemical constituents were evaluated together with engineering calculations describing combustion processes and decomposition chemistry. These analyses established the source terms necessary for subsequent atmospheric dispersion modeling and exposure assessment.
Atmospheric dispersion modeling represented a principal component of the investigation. Previously developed air dispersion models were independently reviewed to evaluate emissions inventories, source characterization, plume rise assumptions, meteorological inputs, receptor placement, terrain characterization, building downwash, atmospheric stability, and model selection. Supplemental emergency response modeling was then conducted using ALOHA to evaluate alternative release scenarios, chemical surrogate compounds, threat-zone distances, and sensitivity analyses under representative meteorological conditions. Multiple modeling approaches were compared to evaluate uncertainty, determine the sensitivity of predicted concentrations to key modeling assumptions, and characterize the range of potential airborne contaminant concentrations experienced by emergency responders and surrounding communities.
The investigation also incorporated detailed toxicological evaluation of both reported emissions and scientifically appropriate surrogate compounds. Because complete characterization of combustion products was not available for every release scenario, surrogate chemicals possessing comparable toxicological and physicochemical properties were selected using accepted emergency response and environmental toxicology methodologies. Published Acute Exposure Guideline Levels (AEGLs), Protective Action Criteria (PACs), Safety Data Sheets (SDSs), regulatory toxicity values, and peer-reviewed toxicological literature were reviewed to characterize acute respiratory hazards, pulmonary toxicity, mucous membrane irritation, delayed lung injury, and other health endpoints relevant to the chemicals evaluated. This toxicological framework allowed modeled airborne concentrations to be interpreted within the context of established health-based exposure criteria.
Exposure assessment integrated atmospheric modeling results with documented responder locations, evacuation activities, incident timelines, and available field observations. Reported locations of emergency personnel and other potentially exposed individuals were compared with modeled plume trajectories, threat-zone boundaries, predicted concentration contours, and emission timing to evaluate the likelihood and duration of inhalation exposure during each release event. Evaluation of exposure incorporated spatial analysis, temporal reconstruction, meteorological variability, and chemical-specific toxicity to estimate potential inhalation hazards associated with the evolving incident. Integration of exposure reconstruction with atmospheric modeling substantially strengthened the assessment by linking modeled airborne concentrations directly with documented human activity during the emergency response.
Finally, the investigation employed accepted principles of uncertainty evaluation fundamental to atmospheric modeling and environmental forensics. Uncertainty associated with source characterization, emission rates, chemical composition, meteorological variability, plume dynamics, combustion chemistry, and human activity patterns was addressed through evaluation of multiple independent data sources, sensitivity analyses, engineering documentation, regulatory investigations, emissions inventories, and alternative atmospheric modeling approaches. Rather than relying upon any single dataset or model output, the investigation synthesized engineering analyses, atmospheric science, toxicology, exposure assessment, and regulatory guidance into a comprehensive weight-of-evidence framework. This multidisciplinary methodology provides a scientifically reliable basis for evaluating complex accidental chemical releases while remaining consistent with accepted principles of air dispersion modeling, environmental chemistry, industrial hygiene, emergency response science, and quantitative human health risk assessment.
Results
Review of the available scientific, engineering, and regulatory documentation demonstrated that characterization of a large-scale accidental chemical release requires integration of emissions reconstruction, atmospheric dispersion modeling, environmental chemistry, industrial hygiene, emergency response science, toxicology, and quantitative human health risk assessment. Although individual emissions inventories and air dispersion models provide important information regarding specific release events, no single technical evaluation independently characterizes the complexity of a multi-day industrial incident involving chemical decomposition, combustion, changing meteorological conditions, and multiple release mechanisms. Accordingly, the investigation integrated multiple independent lines of scientific evidence to reconstruct airborne contaminant releases, evaluate atmospheric transport, characterize potential human exposure, and assess acute inhalation hazards using accepted principles of environmental forensics and exposure science. Collectively, these complementary sources of scientific information provided a comprehensive framework for evaluating complex industrial chemical release incidents.
One of the principal findings of the investigation was the strong agreement between engineering documentation, emissions inventories, atmospheric dispersion modeling, and toxicological evaluations regarding the occurrence of multiple distinct release events involving both thermal decomposition and combustion. Engineering records documented the sequence of wastewater overflows, loss of refrigeration, decomposition of thermally unstable organic peroxide products, combustion of temporary storage trailers, and controlled burn activities. Emissions inventories independently quantified releases of particulate matter, volatile organic compounds, nitrogen oxides, sulfur dioxide, and numerous individual chemical constituents, while atmospheric modeling demonstrated the transport and dispersion of these emissions under observed meteorological conditions. Independent agreement among engineering analyses, emissions calculations, and atmospheric modeling substantially strengthened confidence in the overall reconstruction of the incident.
The investigation further demonstrated the importance of evaluating multiple atmospheric modeling approaches when reconstructing complex accidental releases. Independent review of engineering air dispersion analyses identified assumptions associated with emissions inventories, plume characteristics, source parameters, meteorological inputs, and receptor placement, while supplemental ALOHA modeling provided an additional evaluation of potential airborne concentrations using alternative source assumptions and chemical surrogate analyses. Sensitivity analyses demonstrated how variations in source characterization, atmospheric conditions, and chemical properties influence predicted airborne concentrations and threat-zone distances. Evaluation of multiple modeling approaches therefore provided a more scientifically robust assessment than reliance upon any single atmospheric model alone.
Evaluation of toxicological information also demonstrated the value of integrating atmospheric modeling with chemical-specific health criteria. Published toxicological information, Safety Data Sheets, Acute Exposure Guideline Levels (AEGLs), Protective Action Criteria (PACs), and regulatory toxicity values were reviewed for both reported emissions and scientifically supported surrogate compounds representing decomposition products and combustion byproducts. Comparison of modeled airborne concentrations with established health-based exposure criteria provided a scientifically supported framework for evaluating potential acute respiratory irritation, pulmonary toxicity, delayed lung injury, mucous membrane irritation, and other inhalation hazards associated with the incident. Integration of atmospheric modeling with toxicological evaluation therefore strengthened interpretation of modeled concentrations by relating predicted airborne exposures directly to recognized health-based benchmarks.
The investigation additionally demonstrated the importance of integrating exposure reconstruction with atmospheric science. Reported locations of emergency responders and other potentially exposed individuals were evaluated together with incident timelines, plume trajectories, modeled concentration contours, and meteorological conditions to characterize the timing, duration, and relative magnitude of inhalation exposure during each release event. Rather than evaluating modeled concentrations in isolation, the investigation reconstructed human exposure by combining atmospheric dispersion analyses with documented responder activities and incident chronology. This multidisciplinary approach substantially strengthened exposure assessment by linking environmental modeling directly with real-world exposure scenarios encountered during the emergency response.
Another important finding involved the successful integration of environmental chemistry, atmospheric dispersion modeling, industrial hygiene, emergency response science, engineering analysis, toxicology, exposure assessment, and quantitative human health risk assessment into a unified environmental forensic framework. No individual emissions inventory, atmospheric model, engineering calculation, or toxicological evaluation independently characterized the complexity of the accidental chemical release. However, when engineering documentation, emissions calculations, atmospheric dispersion modeling, meteorological analyses, toxicological investigations, exposure reconstruction, and regulatory evaluations were collectively reviewed, they provided a scientifically supported assessment of airborne contaminant releases and potential human exposure. This multidisciplinary, weight-of-evidence approach represents a fundamental principle of modern environmental forensics and provides a technically reliable framework for evaluating complex industrial accidents involving hazardous airborne chemical releases, emergency response activities, and rapidly evolving atmospheric conditions.
Conclusions
The available scientific and technical documentation provides a comprehensive foundation for evaluating large-scale accidental chemical releases using accepted principles of atmospheric dispersion modeling, environmental chemistry, industrial hygiene, emergency response science, environmental toxicology, contaminant fate and transport, and quantitative human health risk assessment. Although catastrophic industrial incidents frequently involve multiple release mechanisms, evolving meteorological conditions, and uncertainty regarding the identity and quantity of released chemicals, the integration of engineering analyses, emissions inventories, atmospheric dispersion modeling, exposure reconstruction, toxicological investigations, and regulatory guidance provides a scientifically reliable framework for characterizing airborne contaminant releases and evaluating potential human exposure. This multidisciplinary approach allows complex chemical incidents to be evaluated using methodologies that are consistent with accepted scientific practice and widely recognized within the environmental engineering, industrial hygiene, and emergency response professions.
The investigation demonstrated that evaluation of accidental chemical releases is most scientifically reliable when emissions reconstruction, atmospheric dispersion modeling, environmental chemistry, engineering analysis, toxicology, exposure assessment, and regulatory science are considered collectively rather than independently. This weight-of-evidence approach reduces uncertainty by integrating complementary sources of scientific information and provides a technically supported basis for evaluating source characterization, atmospheric transport, chemical transformation, human exposure, and potential health impacts. Independent agreement among engineering records, emissions calculations, air dispersion models, meteorological analyses, and toxicological evaluations substantially strengthens confidence in the overall scientific assessment while recognizing the complexity of reconstructing rapidly evolving industrial emergencies.
The investigation further demonstrated the importance of evaluating chemical releases within the broader context of industrial process safety, thermal decomposition chemistry, combustion processes, meteorological variability, atmospheric transport, emergency response activities, and cumulative inhalation exposure. Large industrial incidents may generate complex mixtures of reactive gases, volatile organic compounds, combustion products, particulate matter, and secondary decomposition products that cannot be adequately characterized by evaluation of a single contaminant or isolated emission event. Comprehensive investigations integrating environmental chemistry, atmospheric science, industrial hygiene, engineering evaluations, and exposure science therefore provide a more technically accurate understanding of accidental releases than evaluations based solely upon emissions inventories or individual air dispersion models. Consideration of these multiple lines of evidence is essential for developing scientifically defensible evaluations of emergency response exposures and community health impacts following industrial accidents.
The investigation also demonstrated the value of integrating multiple atmospheric modeling approaches with toxicological evaluation and exposure reconstruction. Independent review of engineering air dispersion models together with supplemental emergency response modeling provided a comprehensive evaluation of the influence of source characterization, meteorological conditions, plume behavior, chemical properties, and model assumptions on predicted airborne concentrations. Comparison of modeled concentrations with Acute Exposure Guideline Levels (AEGLs), Protective Action Criteria (PACs), Safety Data Sheets, and published toxicological information provided an objective scientific framework for interpreting modeled airborne concentrations within the context of recognized health-based exposure criteria. Integration of atmospheric modeling, toxicology, and documented responder locations therefore provided a substantially more comprehensive evaluation of inhalation exposure than reliance upon modeling or toxicology alone.
More broadly, this investigation demonstrates how modern environmental consulting integrates atmospheric dispersion modeling, environmental chemistry, industrial hygiene, emergency response science, engineering analysis, contaminant fate and transport, environmental toxicology, and quantitative human health risk assessment to evaluate complex accidental chemical release investigations. These multidisciplinary evaluations provide scientifically supported assessments of airborne contaminant releases while remaining grounded in accepted atmospheric modeling principles, peer-reviewed scientific literature, engineering analyses, emissions inventories, toxicological investigations, meteorological science, and objective technical evaluation. By combining emissions reconstruction, engineering analyses, atmospheric dispersion modeling, exposure assessment, and toxicological interpretation, environmental forensic investigations are able to develop reliable assessments of complex industrial accidents that are consistent with recognized scientific practice and contemporary environmental health methodologies.
This investigation was conducted under the direction of Dr. Paul Rosenfeld, an environmental scientist, air dispersion modeler, environmental forensic expert, and exposure assessment specialist with more than twenty-five years of experience evaluating accidental chemical releases, atmospheric dispersion modeling, industrial fires and explosions, environmental chemistry, contaminant fate and transport, emergency response incidents, industrial hygiene, environmental toxicology, and quantitative human health risk assessment. Throughout his career, Dr. Rosenfeld has conducted investigations involving chemical manufacturing facilities, petroleum and chemical plants, industrial fires, explosions, transportation incidents, hazardous material releases, PFAS, volatile organic compounds, particulate matter, combustion byproducts, and numerous other environmental contaminants affecting occupational settings, surrounding communities, and emergency responders. His professional experience includes emissions reconstruction, atmospheric dispersion modeling, exposure assessment, regulatory review, engineering evaluation, environmental site investigations, contaminant fate and transport analysis, and expert witness testimony involving complex environmental contamination, industrial accidents, toxic tort litigation, and emergency response investigations.
References
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Agency for Toxic Substances and Disease Registry (ATSDR). (2024). Toxicological Profile for Chlorine.
Agency for Toxic Substances and Disease Registry (ATSDR). (2024). Toxicological Profile for Hydrogen Fluoride.
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U.S. Environmental Protection Agency (EPA). (2024). Acute Exposure Guideline Levels (AEGLs) and Protective Action Criteria.