The Internal Aerodynamics of Cargo Containers for Trace Chemical Sampling and Detection

Millions of air- and sea-cargo containers enter into and are transported throughout the United States each year. The possibility that some might contain terrorist devices and the impracticability of opening and inspecting them all have become highly charged political issues. However, if the interiors of cargo containers could be quickly sampled for trace explosives without opening them, broad and rapid inspections could be conducted. This would enhance security and allow legitimate cargo to flow almost unimpeded through ports and terminals. Here, we present techniques for nonintrusively sampling cargo containers for trace explosive particles and vapors using external suction devices. The experimental results show the ability to successfully detect explosive contamination and the importance of the internal aerodynamics of the cargo containers. This is studied through flow visualization techniques to reveal the effects of “natural air vents,” container geometry, and packing configurations upon the sampling techniques investigated here. A discussion of optimal trace sampling strategies is given based on these results.