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Modeling Dispersion of Chemical Hazards, using ALOHA PowerPoint Presentation
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Modeling Dispersion of Chemical Hazards, using ALOHA

Modeling Dispersion of Chemical Hazards, using ALOHA

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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