Explosive threat detection instrumentation

As mentioned, new types of homemade explosives or alternates to common nitrated explosives have appeared in several terror scenes and pose a threat to public safety (see Frame 12.3). To counteract these threats, instrumentation has to be calibrated, data systems have to be revised, and some modifications in operational parameters may be necessary. Some of the major manufactnrers of explosive detectors have characterized operational conditions for the detection of several alternative explosives withont severe deterioration of performance for the standard explosives. In one example, the temperature of the drift tube was lowered to 169°C, and the desorber was set to 220°C. In addition, the instrument was operated in dual mode (i.e., measurement of the negative and positive mobility spectra almost simultaneously). With these modifications, operational detection limits (ODLs), defined by the authors as the mass of target substance that was required to produce an alarm at a given detection threshold, of 50 to 100 ng were established for TATP, ammonium nitrate, and gunpowder. These detection limits have been improved with the cnrrent generation of explosive detectors, especially for TATP. Under these conditions, the response and detection limit for TNT is degraded by a factor of two, but those for RDX and NG are barely affected the detection limit for PETN was improved. ... 

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