Steven Hanna1*, Joseph Chang2, Thomas Spicer3, Michael D. Sohn4, Shannon Fox5, Mark Whitmire6, Leo Stockham7, Allison Hedrick8, Donald Storwold8, Erik Vernon8, Thomas Mazzola9
1Hanna Consultants, Kennebunkport, ME; 2Homeland Security Studies and Analysis Institute, Falls Church, VA; 3Univ Arkansas, Fayetteville, AR; 4Lawrence Berkeley National Laboratory, Berkeley, CA; 5DHS S&T Chemical Security and Analysis Center (CSAC), Aberdeen Proving Ground, MD; 6Noblis, Falls Church, VA; 7Leidos, Albuquerque, NM; 8Dugway Proving Ground, UT; 9Engility, Lorton, VA
*Hanna Consultants, 7 Crescent Ave., Kennebunkport, ME 04046-7235
(207 967 4478, hannaconsult@roadrunner.com)
The Jack Rabbit II field experiment, carried out in August and September 2015 at Dugway Proving Ground, Utah, involved five releases of 5 to 10 tons of pressurized liquefied chlorine in an artificial built “mock urban” environment consisting of about 80 CONEX containers (2.3 by 2.6 by 6.1 or 12.2 m) covering a gravel area about 122 m square. There were 12 rows of CONEXs, with 4 to 9 per row. The source was located on a 25 m diameter concrete pad inside the CONEX array about four rows from the upwind edge. In addition, some trailers and a taller stack of two wide by three high CONEXs were placed about 70 m downwind of the source, to study the transport, dispersion, and deposition of dense chlorine gas around and inside the structures. Pressurized liquefied chlorine was released from a six-inch opening at the bottom of a tank mounted about 1.0 m agl, resulting in a downward-directed two-phase momentum jet lasting a minute or less. Wind speeds at a height of 2 m ranged from 2 to 5 m/s during the five trials. Concentrations were measured within the obstacle array and on arcs at distances of 200 m, 500 m, and 1, 2, 5, and 11 km. Twenty samplers were used within the obstacle array and 13 of them could measure chlorine concentrations up to about 120,000 ppm (i.e., 12 % by volume). Samplers were also placed inside the trailers and the stacked structure.
Sonic anemometers were not installed within the obstacle array when the chlorine gas would be present, because of possible damage by the chlorine cloud. Instead, a few weeks after the chlorine releases, a separate study took place with 29 sonic anemometers placed near the stack of two-wide by three-high CONEXs and one of the 12.2 m long single CONEXs. These allowed the mean winds and turbulence and fluxes to be determined in the recirculating vortices around the two structures. In addition, a 32 m tower with 5 sonic anemometer levels was located about 30 m upwind of the CONEX array during the chlorine release trials and the special sonic study.
During the 30 to 60 s release period, the initial chlorine jet formed a broad and shallow dense wall jet that rapidly spread in all directions to a distance of about 50 to 75 m, before moving with the wind across the urban array and over the desert surface downwind. When the wall jet encountered obstacles, it mixed up and around them. The resulting initial chlorine cloud had a depth of about 1½ times the CONEX heights, but then “settled down” due to density effects after the momentum jet stopped. Some liquid pooling was observed and the magnitude is being estimated in various ways.
The quantitative concentration observations and the many photos and videos have completed QA/QC, and this paper describes some results of preliminary analysis. For example, the decrease of concentration and the increase of cloud width with distance are seen to follow basic dense gas similarity relations. The mean and turbulent wind observations from the sonic anemometer study have just recently been released and the results of the first phase of analysis will be presented.
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