Comparison of chlorine and ammonia concentration field trial data with calculated results from a Gaussian atmospheric transport and dispersion model.

The Jack Rabbit Test Program was sponsored in April and May 2010 by the Department of Homeland Security Transportation Security Administration to generate source data for large releases of chlorine and ammonia from transport tanks. In addition to a variety of data types measured at the release location, concentration versus time data was measured using sensors at distances up to 500 m from the tank. Release data were used to create accurate representations of the vapor flux versus time for the ten releases. This study was conducted to determine the importance of source terms and meteorological conditions in predicting downwind concentrations and the accuracy that can be obtained in those predictions. Each source representation was entered into an atmospheric transport and dispersion model using simplifying assumptions regarding the source characterization and meteorological conditions, and statistics for cloud duration and concentration at the sensor locations were calculated. A detailed characterization for one of the chlorine releases predicted 37% of concentration values within a factor of two, but cannot be considered representative of all the trials. Predictions of toxic effects at 200 m are relevant to incidents involving 1-ton chlorine tanks commonly used in parts of the United States and internationally.

A guided tour of COMPASS.

The COMPASS software was designed to facilitate the use of MARSSIM and guide the user into making informed decisions in designing final status radiological surveys. COMPASS also simplifies the application of the statistical tests by performing the statistical calculations and providing prospective power curves that help in determining what level of confidence the user is willing to accept for a particular number of measurements or samples for a survey unit. After performing the final status survey, COMPASS assesses the data for comparison to the release criteria. The purpose of this article is to provide the COMPASS user with an overview of the features of the software and to demonstrate how COMPASS implements the MARSSIM guidance.