Ongoing TSA disperion modeling activities
16th Joint Conference on the Applications of Air Pollution Meteorology with the A&WMA, 17-21 January 2010, Atlanta, Georgia
The Freight Rail Division of the TSA and the Chemical Security Analysis Center of the DHS are conducting a task to improve expected-value modeling capabilities for large scale TIH releases. The task is intended to identify knowledge and modeling gaps and facilitate filling in those gaps through analysis and testing. The end users are first responders, site safety planners, and regulators.
We note the well-documented discrepancies between actual results and model system outputs for several recent large scale releases of chlorine resulting from railcar breaches. After evaluation of official reports, prior testing, and CFD modeling results, we have focused on gravitational settling and the resulting persistent dense-gas clouds as a possible cause of the discrepancies. This effect is expected to occur when large amounts of superheated liquids are released under stable atmospheric conditions, though it has only occasionally been observed during small or mid-scale ( one ton ) releases.
We present plans for a series of field tests to identify the major parameters governing this phenomenon and to quantify the effects of this change to the source term on dispersion modeling and consequence assessment. Accidental releases seem to indicate a severe down-slope hazard persisting for hours and a less severe down-wind hazard as compared to model results. This has important implications for first-response and regulatory rule-making.
Additional areas of TSA-sponsored research will be presented including chemical reactions in the environment and improvements in expected-value toxicology parameters.