J14.1 SOURCE EMISSIONS AND TRANSPORT AND DISPERSION MODELS FOR TOXIC INDUSTRIAL CHEMICALS (TICs) RELEASED IN CITIES

The major scientific issues concerning source emissions models and dispersion models for Toxic Industrial Chemicals (TICs) are discussed, with emphasis on chemicals stored and/or transported as pressurized liquefied gases (e.g., chlorine, anhydrous ammonia, and sulfur dioxide). Many tons of a gas/aerosol mixture can be released and have been released into the atmosphere in one or two minutes in railcar accidents. Some recommendations are given for specific source emissions equations, with scientific rationale provided. Field experiments on TIC source emissions are reviewed and some results of evaluations of models for droplet formation in flashing jets are presented. The characteristics of various dispersion models for TIC releases in urban areas are reviewed. A hypothetical chlorine railcar release in Chicago is simulated with a CFD model (FLACS) and with several widely-used simpler models and the results compared. The CFD model-simulated effects of the urban buildings on the dense gas transport and dispersion are discussed, such as constraints by buildings near the source, reductions in transport speed, diversion of the dense gas down drainage slopes, increases in turbulence intensities, and hold-up in building wakes after the main cloud has passed