I


EDs prepared from high explosives, such as nitrated organic compounds, including TNT and RDX, are difficult


to prepare in ‘back-yard clandestine laboratories’ as the required constituents are highly regulated and difficult to procure.


Furthermore, the


procedures to make military explosives are complex, at times dangerous and require industrial grade equipment. As a result, explosives based on inorganic salts and/or organic peroxides, which are easy to prepare from materials that are relatively cheap and generally readily available, are more conducive to illicit back-yard manufacturing.


This


ease of preparation has made such materials a popular choice for terrorists when preparing homemade explosives. Due to the increase in terrorist attacks over the last two decades the ability to detect explosives, or those who have


Analysis of explosives can be grouped


into two main classifications: detection and identification of explosives before detonation (pre-blast analysis) and identification and analysis of debris following detonation (post-blast analysis). Both areas are important and in many cases procedures for pre- and post-blast analysis are similar as many of the diagnostic species of interest will be present both before and after the blast, especially in the case of inorganic based explosives. As with most things, prevention is better than cure and as such pre-blast analysis, with its emphasis on preventing the use of IEDs, is desirable due to its ability to save lives and protect property. The main problem with pre-blast analysis is the need for fast analysis and detection methods since many of the high risk targets such as airports, train stations and public events deal with high throughput


have been in place for some time and are now found in most major airports. These analyse a direct sample taken via a swab wiped over any surface, however their applicability to the inorganic salts and/or peroxide based explosives is limited since the nature of these species do not lend themselves to IMS analysis. Organic peroxides such as triacetone triperoxide (TATP), for example, are too volatile, resulting in large doses being required for successful IMS detection1


,


albeit that some units can detect some of the precursors (acetone or hydrogenated water) to TATP. Though the volatility


of TATP is a


hindrance for IMS, it can also be an advantage when using other techniques. Takada et al constructed a walkthrough detection portal and monitored TATP vapour using mass spectrometry (MS)2 The detection portal comprised a gate


.


Improvised explosive devices (IEDs) and homemade explosive devices (HMEs) have long been used by terrorist groups due to their advantages in terms of destructive power, the relatively small quantities of material required, the ease with which they can be transported and concealed, and the fact that many of the formulations can be constructed from easily obtained and non-restricted materials. Philip Zakaria, Greg W. Dicinoski and Michael C. Breadmore look at the challenges in detecting homemade IEDs and potential solutions to the problem.


been involved in their preparation, is vital for maintaining the safety and stability of society in general.


Because of their ease of preparation this article will focus on the detection and identification of the inorganic salts and/ or organic peroxide based explosives. Such explosives have commonly been used in recent times including in the Bali bombings of 2002 (chlorate, sulphur, aluminium), Pune, India in 2010 (ammonium nitrate fuel oil), Oslo, Norway in 2011 (fertiliser and fuel oil), the shoe bomb plot of 2001 (TATP was used in the detonating arrangement, albeit PETN, which is not peroxide-based was the main charge), the London bombings of 2005, and the transatlantic liquid explosives airline plot of 2006 (all organic peroxide based devices).


February 2012 Aviationsecurityinternational traffic.


Analysis speed, however, is generally achieved at the expense of accuracy.


This interplay between speed and accuracy is a major challenge when detecting IEDs and much of the current research relates to the improvement of either one, or ideally both, of these facets. That said, false alarm rates and, of course, cost, are additional trade-offs that must also be considered. Pre-blast analysis can either be direct, i.e. samples are taken from the person or item being examined and directly analysed, or it can be performed in a ‘standoff’ manner where the instrumentation is housed some distance from the person or item with detection taking place via various spectral means. Direct pre-blast analysis in the form of ion mobility spectrometry (IMS) units


through which people or bags could pass. A stream of heated air was continually pushed over the gate with the sampling ports collecting the air at 2 L/min followed by subsequent introduction into the MS system (see below).


Walkthrough portal system used by Takada et al. (Credit: Takada et al.)


www.asi-mag.com 17


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