Comparing Results of Two Chlorine Release Field Experiments—Wild Stallion and Jack Rabbit

Two large scale field experiments have taken place in the last three years – The Wild Stallion (WS) and the Jack Rabbit (JR) experiments. Both involved releases of pressurized liquefied chlorine near the ground and both took place at Dugway Proving Ground. WS used one ton chlorine cylinders and JR used two ton chlorine cylinders. However, because of the differing source release configurations and meteorological conditions, the resulting chlorine clouds looked quite different. This paper compares and contrasts the two field experiments and suggests scientific reasons for the differences that were seen. The source orientations were different primarily because of differing goals of the experiments. WS was addressing releases caused by explosive devices over the open flat desert during the daytime. Thus the chlorine cylinders were ruptured in specific ways and the momentum jet, of duration 30 s for the smaller hole and one second for the larger hole, was oriented horizontally or at an upward angle. Also the wind speeds were moderate (not light) at WS. As a result, the WS chlorine jet “looked like” a vigorous jet at all times, extending outward 50 m or more, and forming a large (50-100 m diameter) hemispherical cloud of chlorine gas and aerosol, part of which subsequently slumped towards the ground, and then moved downwind. However, JR was addressing the specific issue of chlorine released towards the ground from a short 3 inch pipe with a controlling valve, and forced confinement (initially) in a depression of 2 m depth and 50 m diameter during light winds in the early morning. Indeed, with wind speeds less than about 1 or 2 m/s, the gas and aerosol cloud was largely confined in the depression for the first minute or so, after which it was scoured out of the depression and moved downwind. There was an obvious axisymmetric dense “wall (or ground) jet” seen while the release occurred over about 30 s. At wind speeds exceeding 1 or 2 m/s during JR, the initial cloud was not well-confined in the depression and moved downwind. Some scientific explanations for the observed differences between WS and JR are provided in this paper, based on basic fluid dynamic principles and similarity arguments.