Jack Rabbit II – A Field Experiment on Dense Gas Dispersion in a Built Environment

The Jack Rabbit II field experiment, carried out in August and September 2015 at Dugway Proving Ground, Utah, involved releases of 5 and 10 tons of pressurized liquefied chlorine in an artificial built “mock urban” environment consisting of about 80 CONEX containers (2.3 m wide by 2.6 m high by 6.1 or 12.2 m long) in a staggered array covering an area of about 122 m by 122 m. Two medium sized trailers, one CONEX, and a taller stack of two wide by three high CONEXs are also placed about 70 m downwind of the source close to the edge of the mock urban array, and are used to study (1) the transport and dispersion of dense gas around the structures, and (2) vertical mixing indoors in the presence of gas stratification. On some of the trials, another two-wide by three tall stack of CONEXs is place about 10 m upwind of the source, to study the vertical spread of dense gas in the less of a nearby tall building. Near dawn on each trial day, the chlorine is released in about one or two minutes from a height of about 1.0 m as a strong downward-directed two-phase momentum jet, which subsequently forms a broad and shallow dense cloud. The objective is to assess the flow and dispersion of the dense cloud in a built environment. A field experiment of this type cannot be carried out in a “real” urban area because of the health hazard associated with such large releases of chlorine. Beyond the urban area, concentration samplers are set up on arcs at distances of 200 m, 500 m, and 1, 2, 5, and 11 km.

The field experiment design is presented along with several scientific issues that had to be addressed in the planning. Results from previous field experiments and from various available model runs have been used to locate instruments, including several towers with concentration measurements at two or three heights. Although the quantitative observations have not yet gone through QA/QC, some preliminary qualitative examples of photos and videos are presented.