Persistence of explosives under real world conditions

Abstract

Those that handle explosives materials invariably become contaminated with particulates of materials, which become entrapped in the grooves of the fingers and are then transferred by contact to other surfaces. These particles provide an evidentiary trail which is useful for security applications, a fact which is enhanced by the fact that many explosives materials of interest have low vapor pressures, augmenting their longevity. The persistence or stability of explosives particles on a substrate is a function of several environmental parameters or particle properties, including vapor pressure, particle size and geometry, airflow, particle field size, substrate topography, humidity, reactivity, adlayers, admixtures, particle areal density, and temperature. In this work we deposited particles of 2,4-dinitrotoluene on standard microscope glass slides by particle sieving and studied their sublimation as a function of temperature and relative humidity. A custom airflow cell allowed us to monitor the particles with in situ photomicroscopy while keeping the airflow over the particles, substrate type, and areal field size constant for each experiment. We define the size-independent radial sublimation velocity for the equivalent sphere of a particle as the parameter to characterize the sublimation rate. The dependence of the sublimation rate for an ensemble of particles on temperature was quantified according the radial sublimation velocity, while the sublimation of 2,4-dinintrotoluene was found to independent of relative humidity between 25-90%.