Handling Input Data Gaps in Modeling Accidental releases of Hazardous Chemicals during Transportation

A transportation accident involving releases of hazardous chemicals to the atmosphere can happen anywhere and anytime. Two examples that are discussed are the chlorine release from a punctured railcar following a train accident in 2005, and the anhydrous ammonia release from a nurse tank being towed by a tractor to an agricultural field in 2019. During the hazardous release period and during the emergency response period following such accidents, adequate input information is seldom available for transport and dispersion modeling. Even when retrospective or historical analysis is done much later, key observations, such as local winds and stability, underlying soil type, high resolution terrain, and emissions conditions, may be missing. This paper describes some of these input data gaps, with emphasis on meteorological inputs, and ways to address the uncertainties in modeling. For example, pros and cons of using closest airport versus NWP model winds are presented.