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Modeling Dispersion of Chemical Hazards, using ALOHA

Modeling Dispersion of Chemical Hazards, using ALOHA. Prepared by Dr. Erno Sajo, Associate Professor, Department of Physics and Astronomy, Louisiana State University. Objectives. 3.1 Define the nature of the hazards associated with the air dispersion of hazardous chemicals.

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Modeling Dispersion of Chemical Hazards, using ALOHA

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  1. Modeling Dispersion of Chemical Hazards, using ALOHA Prepared by Dr. Erno Sajo, Associate Professor, Department of Physics and Astronomy, Louisiana State University Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  2. Objectives • 3.1 Define the nature of the hazards associated with the air dispersion of hazardous chemicals. • 3.2 Discuss the interaction of air dispersion of hazardous chemicals with the natural environment. • 3.3Discuss the goals and objectives of air dispersion modeling of hazardous chemicals, specific to the intended user. • 3.4 Outline the capabilities of the ALOHA model and discuss data requirements. • 3.5 Review available results and discuss importance to different user groups. • 3.6 Discuss the application of ALOHA air dispersion model results for both planning and emergency management operations. Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  3. Overview of Atmospheric Dispersion • The effects of atmospheric motions on suspended pollutants • Effects of large size turbulence • Effects of small turbulence • Particle pollutants & gaseous pollutants • Behavior of cold or dense gas • Behavior of hot gas • Behavior of buoyant gas • Behavior of mixtures • Behavior of particulates and aerosols • Dispersion in urban and rural environments Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  4. Sources of Air Pollutants • Industrial process accidents • Transportation accidents • Routine industrial fugitive emissions • Nuclear, chemical or biological terrorism • Source geometry as a factor impacting air pollutant sources Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  5. Consequences of Nuclear, Chemical & Biological Releases • Concentration of the release & health impacts • Concentration by specific locations (points) • Doses for radioactive materials • Distribution of observed or calculated concentrations • Level of concern (LOC) or threshold concentration • Comparison of concentration distribution & LOC • Comparison of radiation dose & regulatory standards Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  6. Types of Hazard from Atmospheric Releases • Direct exposure (inhalation, skin or eye contact) • Indirect exposure (radiation) • Contaminated food or water supply • Pathways of pollutants from food or water • Terrestrial or aquatic pathways • Classification of pathways Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  7. Importance of Hazard of Airborne Pollutants • Protection of life and human health • Protection of property • Vulnerability of population near chemical sites or transportation routes • Clearer ways to describe behavior of hazards Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  8. Meteorology and Boundary Layer • Wind factors • Vertical temperature structure & stability • Surface roughness • Meteorological instrumentation Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  9. Source Term, Dilution & Plume Rise • Release parameters from source • Release parameters of the chemical • Plume rise • Release height for buoyant sources • Volume & area point sources • Building effects Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  10. Dispersion of Neutrally Buoyant Gases • The plume is not rising nor sinking • Equal probability of spreading in different directions • Neutrally buoyant gases are described using Gaussian statistics or normal distributions Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  11. Dispersion of Heavy Gases • Types of heavy gases • Gravitational spreading • Phases of heavy gas dispersion • Release • Transition • Dispersion Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  12. Goals of Modeling Atmospheric Dispersion • Assess nature & extent of hazard • Enhance preparedness • Assess actions to be taken • Examine evacuation routes Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  13. Atmospheric Dispersion Models • Types of models and data requirements • Computer requirements • Limitations of computational models • Uncertainties in modeling Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  14. Air Dispersion Models • Models specific for type of release • Industrial Source Complex (ISC3-ST) • CALPUFF & SCIPUFF (buoyant gas) • DEGADIS & SLAB (heavy gas) • ALOHA (both buoyant & heavy gas releases) Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  15. ALOHA Capabilities and Data Requirements • Meteorological data requirements • Chemical database • Capabilities • Automatically determines heavy or buoyant gas • Models emissions from many sources • Predicts indoor & outdoor sources • Displays concentration footprint Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  16. ALOHA (continued): Limitations • Does not account for the following: • terrain effects or building effects • radioactive materials or particulates • Chemical mixtures • Deposition rates • Effects of rain or fog • Releases into water bodies • Duration limited to 1 hour • Release area limited to 10 km. • Minimum distance to source is 100 m. Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  17. Dispersion Model Results • Footprints (concentration isopleths) • Dose or dose rate • Deposition isopleths • Probabilities of exposure Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  18. ALOHA Users • Emergency managers & responders • Emergency planners • Toxicologist • Health Physicits Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  19. ALOHA Scenario • In a transportation accident near Baton Rouge, LA, a 9000 Gallon tank truck carrying ammonia overturns and shears off a flange whose diameter is 4 inches. The size of the tank is 24 feet long and 8 feet in diameter. The tank contains liquid, which is stored at ambient temperature. The fill density of the tank is 75% by volume. The sheared-off flange creates a circular opening of about 3 inches in diameter, and it is located at 30% of the way to the top of the tank. • At the time of the accident, the wind direction is NE (i.e. blowing from NE), the wind speed is 5 m/s, measured at 10 m height. The accident occurred on a highway near a small village. The weather is partly cloudy, 50% relative humidity, and the temperature is 12 degrees Celsius. Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

  20. Evaluating Hazard Models • Quality • Do the results accurately reflect the event? • Are the limitations of the model clearly stated? • Is information presented in an orderly manner? • Timeliness • Is the information provided when needed? • Is the information up to date? • If the scenario changes, does the model reflect the change? • Completeness • Is the model complete? • Does the user have access to past model runs? • Does the model provide appropriate information? • Does the model give too much information? Session 11: Modeling Dispersion of Chemical Hazards, using ALOHA

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