Comparison of Six Widely-Used Dense Gas Dispersion Models for Three Actual Railcar Accidents
The simulations are compared of six widely-used dense gas dispersion models of downwind chlorine gas concentrations following three railcar accidents. The six models are ALOHA, HGSYSTEM, SLAB, SCIPUFF, PHAST and TRACE. The three railcar accidents, where as much as 60 t of chlorine were released, are Festus, MO (release from a ruptured 1 in. line while offloading), and Macdona, TX, and Graniteville, SC (release from a large hole due to an accident). Input data were obtained from public sources. Source emissions rates were refined based on source modeling with PHAST and TRACE and derivations using fundamental thermodynamic equations. When using the same source emissions rates, the models’ simulations of 10-minute averaged cloud centerline concentration, at downwind distances ranging from 0.1 to 10 km, agree with each other within plus and minus a factor of two most of the time. For a very large release (Graniteville), the 10-minute averaged 2000 ppm, 400 ppm, and 20 ppm contours are predicted to extend downwind about 1.3, 3.1, and 14 km, respectively, from the source. There is also agreement among the models simulations of the plume widths and heights to the 2000, 400, and 20 ppm contours. A major conclusion of the study is that estimation of the source or release term is important for reliable results.
KeywordsChlorine railcar accidents dense gas models dispersion model comparisons
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- Ermak DL (1990) Users Manual for SLAB: An Atmospheric Dispersion Model for Denser-than-Air Releases. UCRL-MA-105607, Lawrence Livermore National Laboratory, Livermore, CA.Google Scholar
- Hanna SR, Chang JC, Strimaitis DG (1993) Hazardous gas model evaluation with field observations, Atmos. Environ. 27A, 2265-2285.Google Scholar
- Hanna SR, Drivas PJ, Chang JC (1996) Guidelines for Use of Vapor Cloud Dis-persion Models, Second Edition. Published by AIChE/CCPS, 345 East 47th St., New York, NY 10017, 285 pp. + diskette.Google Scholar
- NOAA/HMRAD and EPA/CEPPO (1992) ALOHA Users Manual and Theoretical Description. Reports available from NOAA/HMRAD, 7600 Sand Point Way NE, Seattle, WA 98115 and on CAMEO/ALOHA web site.Google Scholar
- SAFER Systems (1996) Description of Modeling Algorithms, TRACE Version 8.0. Looseleaf notebook available from SAFER Systems, 4165 E. Thousand Oaks Blvd., Suite 350, Westlake Village, CA 91362.Google Scholar
- Sykes RI, Parker SF, Henn DS (2004) SCIPUFF Version 2.1 Technical Documen-tation, Titan Corporation, P.O. Box 2229, Princeton, NJ, 292 pp.Google Scholar
- Witlox HWM, Holt A (1999) A unified model for jet, heavy and passive dispersion including droplet rainout and re-evaporation”, International Conference and Workshop on Modelling the Consequences of Accidental Releases of Hazardous Materials, CCPS/AIChE, San Francisco, California, September 28-October 1, 315-344.Google Scholar