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Metal-containing compounds form a large and rapidly expanding group of high-energy materials. Many compounds in this class attract the attention of non-professionals, who may attempt the illegal production of explosives. Several of these substances have been commercially available and pose significant danger if used by terrorists or for criminal purposes. Others are experimental compounds, kinds of curiosities, often created by pyrotechnics enthusiasts, which can present serious risks to both the creators and their immediate surroundings. The internet hosts a vast amount of information, including recipes and discussions on forums, private websites, social media, and more. This paper aims to review the variety of metal-containing explosives and discuss their appeal and potential accessibility to unauthorized individuals.

With the ever-increasing threat of improvised explosive devices (IEDs) and homemade explosives (HME) both domestically and abroad, detection of explosives and explosive related materials is an area of urgent importance for preventing terrorist activities around the globe. Canines are a common biological detector used in explosive detection due to their enhanced olfactory abilities, high mobility, efficient standoff sampling, and optimal identification of vapor sources. While other sensors based on different principles have emerged, an important concept for the rapid field detection of explosives is understanding key volatile organic compounds (VOCs) associated with these materials. Explosive detection technology needs to be on par with a large number of threats including an array of explosive materials as well as novel chemicals used in the manufacture of IEDs. Within this much needed area of research for law enforcement and homeland security applications, several studies have sought to understand the explosive odor profile from a range of materials. This review aims to provide a foundational overview of these studies to provide a summary of instrumental analysis to date on the various types of explosive odor profiles evaluated focusing on the experimental approaches and laboratory techniques utilized in the chemical characterization of explosive vapors and mixtures. By expanding upon these concepts, a greater understanding of the explosive vapor signature can be achieved, providing for enhanced chemical and biological sensing of explosive threats as well as expanding upon existing laboratory-based models for continued sensor development. [Display omitted] •Detection of explosives and their related materials is an area of urgent importance.•Understanding of volatile organic compounds (VOCs) is key to rapid field detection of explosives.•Enhanced olfactory abilities and high mobility makes canines an excellent tool in biological detection of explosives.•Explosive detection technology must stay up to date with current and expanding threats.•Experimental techniques provide understanding of explosive vapor odor signatures for enhanced sensor development.

The use of organic peroxides for the preparation of homemade explosives (HMEs) is common among terrorists due to inexpensive precursor chemicals and simple synthetic procedures. Triacetone triperoxide (TATP) is the most notable peroxide explosive, and has been deployed in several terrorist attacks as explosive filling of improvised explosive devices (IEDs). Forensic identification of TATP in pre-blast and post-blast residues, including on-site analysis, poses significant analytical challenges and induces demand for practicable and sensitive detection techniques. This work presents a concept suitable for laboratory and on-site identification of TATP residues in liquid samples (aqueous TATP synthetic waste) and in gas phase. It is based on TATP enrichment from the aqueous or gas phase using different types of passive samplers (polydimethylsiloxane (PDMS) sampling rods and activated carbon sampling tubes (ACST)) and subsequent identification of the explosive by gas chromatography-mass spectrometry (GC-MS) or GC with positive chemical ionization and tandem MS (GC-PCI-MS/MS) analytical techniques. Additionally, investigation of the stability of TATP in aqueous solutions and of the stability of enriched TATP in passive samplers under different storage conditions, as well as development of TATP re-extraction procedures from passive samplers have been performed in this study. The practical use of passive samplers was demonstrated during and after TATP production processes. Moreover, post-blast sampling of TATP under different conditions of controlled blasting events was investigated using the passive sampling concept. [Display omitted] •A novel sampling approach for triacetone triperoxide (TATP) detection in gas and liquid phase was developed.•Stability and adsorption kinetics of TATP were investigated for activated charcoal and polydimethylsiloxane (PDMS) samplers.•An internal standard GC-PCI-MS/MS quantification method using 13C-labelled TATP was successfully developed.•The application of passive samplers was demonstrated by successful trials in real pre-blast and post-blast scenarios.

ABSTRACT Homemade explosives (HMEs), commonly used in improvised explosive devices (IEDs), present a significant forensic challenge due to their chemical variability, accessibility and adaptability. Traditional forensic methodologies often struggle with environmental contamination, complex sample matrices and the non‐specificity of precursor residues. Recent advances in analytical techniques and chemometric methods have enhanced the detection, classification and interpretation of explosive residues. Infrared (IR) spectroscopy and gas chromatography–mass spectrometry (GC–MS) have seen improvements in spectral resolution and real‐time detection capabilities, allowing for more accurate differentiation of explosive precursors. Thermal analysis techniques, such as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), now provide refined kinetic modelling to assess the decomposition pathways of unstable energetic materials, improving forensic risk assessments. Additionally, x‐ray diffraction (XRD) has contributed to forensic material sourcing by distinguishing between industrial‐grade and improvised explosive formulations. Chemometric approaches, including principal component analysis (PCA), linear discriminant analysis (LDA) and partial least squares discriminant analysis (PLS‐DA), have revolutionized forensic data analysis by improving classification accuracy and enabling automated identification of explosive components. Advanced machine learning models are being integrated with spectral datasets to enhance real‐time decision‐making in forensic laboratories and portable field devices. Despite these advancements, challenges remain in adapting laboratory‐based techniques for field deployment, particularly in enhancing the sensitivity and robustness of portable analytical instruments. This review critically evaluates the latest developments in forensic analytical chemistry, highlighting strengths, limitations and emerging strategies to improve real‐world HME detection and classification.

•Follow-up of the unique study on the explosive ETN by two research groups.•ETN samples were synthesized using a wide variety of selected precursor sources.•IRMS analysis of ETN and its precursors for chemical attribution.•Isotope ratios allow for ETN sample comparison independent of age and appearance.•IRMS data is useful to investigate which raw materials were used for ETN synthesis. In this follow-up study the collaboration between two research groups from the USA and the Netherlands was continued to expand the framework of chemical attribution for the homemade explosive erythritol tetranitrate (ETN). Isotope ratio mass spectrometry (IRMS) analysis was performed to predict possible links between ETN samples and its precursors. Carbon, nitrogen, hydrogen and oxygen isotope ratios were determined for a wide variety of precursor sources and for ETN samples that were prepared with selected precursors. The stability of isotope ratios of ETN has been demonstrated for melt-cast samples and two-year old samples, which enables sample comparison of ETN in forensic casework independent of age and appearance. Erythritol and nitric acid (or nitrate salt) are the exclusive donor of carbon and nitrogen atoms in ETN, respectively, and robust linear relationships between precursor and the end-product were observed for these isotopes. This allowed for defining isotopic enrichment ranges for carbon and nitrogen that support the hypothesis that a given erythritol or nitrate precursor was used to synthesize a specific ETN batch. The hydrogen and oxygen atoms in ETN do not originate from one exclusive donor material, making linkage prediction more difficult. However, the large negative enrichments observed for both isotopes do provide powerful information to exclude suspected precursor materials as donor of ETN. Additionally, combing the isotopic data of all elements results in a higher discrimination power for ETN samples and its precursor materials. Combining the findings of our previously reported LC–MS analysis of ETN with this IRMS study is expected to increase the robustness of the forensic comparison even further. The partially nitrated impurities can provide insight on the synthesis conditions while the isotope data contain information on the raw materials used for the production of ETN.

The detailed chemical characterization of homemade explosives (HMEs) and other chemicals that can mimic or mask the presence of explosives is important for understanding and improving the performance of commercial instrumentation used for explosive detection. To that end, an atmospheric-pressure drift tube ion mobility spectrometry (IMS) instrument has been successfully coupled to a commercial tandem mass spectrometry (MS) system. The tandem MS system is comprised of a linear ion trap and a high resolution Orbitrap analyzer. This IMS-MS combination allows extensive characterization of threat chemical compounds, including HMEs, and complex real-world background chemicals that can interfere with detection. Here, the composition of ion species originating from a specific HME, erythritol tetranitrate, has been elucidated using accurate mass measurements, isotopic ratios, and tandem MS. Gated IMS-MS and high-resolution MS have been used to identify minor impurities that can be indicative of the HME source and/or synthesis route. Comparison between data obtained on the IMS/MS system and on commercial stand-alone IMS instruments used as explosive trace detectors (ETDs) has also been performed. Such analysis allows better signature assignments of threat compounds, modified detection algorithms, and improved overall ETD performance. Graphical Abstract ᅟ

This paper presents a new approach, in handling data (encoding, managing and retrieving) in secure sensitive and classified organisations (such as Law Enforcement Agencies (LEAs)), that utilises Web 3.0 technologies as well as knowledge management techniques and pushing of information. This approach signals a departure from current use of databases and pulling of information technologies as well as allowing separation of concerns between how data are organised/structured and how data are manipulated/processed. Such an approach utilises an adaptive knowledge management platform capable of supporting organisational operations of LEAs using data aggregated from assorted, heterogeneous and online sources. Such knowledge is then pushed to the users, using recommenders, in an effortless manner addressing the needs of the organisation. Moreover, the system is designed to afford easier change of operational needs through the addition and removal of multiple folksonomies (representing changes in focus or new trends). These changes are further enriched with semantics providing specialised domain-specific content recommendations and semantically enriched search capabilities. This approach to knowledge retrieval has been applied to the domain of homemade explosives and counter-terrorism efforts as part of the HOMER project, where data are aggregated from sources such as police databases, online forums and explosives wikis. Data are stored in an unstructured manner and annotated by the users, ultimately being categorised as per the knowledge retrieval needs of the organisation, which in this case is to carry out efficient and effective investigations regarding homemade explosives. We describe the architecture of a system that can efficiently and effectively support related investigatory activities, and we also present an evaluation from the perspective of the end-users.

Understanding the properties of explosives is the basis for investigating and analyzing explosion cases. To date, due to the strict legal control of standard explosives and initiators, homemade pyrotechnics composed of oxidizers and fuels have become popular explosive sources of improvised explosive devices (IEDs) threatening greatly social stability and personal safety. The reactivity of pyrotechnics strongly depends on their intrinsic characteristics and operating conditions, which determine the efficiencies of heat and mass transfer between the reaction zone and the unreacted zone. Herein, the tests of thermodynamics, pressurization characteristics, and combustion propagation behaviors are conducted to explore the effects of oxidizer species, particle size, and loading density on the reactivity of homemade binary aluminum-based pyrotechnics. The results show that the pyrotechnics with potassium chlorate (KClO 3 ) have the strongest reactivity with the highest pressurization rate (d p /d t ) and the shortest combustion duration. Compared with their counterparts based on aluminum microparticles(mAl), pyrotechnics consisting of Al nanoparticles (nAl) possess superior reactivity as expected, which results from the relatively short heat and mass transfer distances. The nAl-based pyrotechnics have a low reaction exothermic peak temperature, great heat release, great aluminothermic reaction completeness, and high produced peak pressure with several orders of magnitude higher pressurization rate. Increasing the loading density of the pyrotechnics over a certain value can change the dominant mode of heat transfer from convective to conduction, sharply decreasing the pressurization characteristics and combustion front propagation velocities ( v p ). The results of theoretical calculations using the NASA-CEA codes show that loading density can alter the reaction process of the pyrotechnics, leading to a decrease in the predicted pressure per unit mass for Al/KNO 3 or Al/AP, and an increase for Al/KClO 3 . For nAl/potassium nitrate (KNO 3 ), the density is between 1.0 and 1.25 g cm −3 , across which d p /d t decreases by one order of magnitude from 0.148 to 0.014 MPa ms −1 . In addition, v p decreases by three orders of magnitude from 0.040 to 0.078 m s −1 . Distinct pressurization behaviors of nAl/AP are observed at a density of 1.5 g cm −3 , while the variation in nAl/KClO 3 reactivity fluctuates. These results are beneficial for the damage assessment of scenes caused by an explosion and for inversely calculating charge parameters.

Tephra fall is a major volcanic hazard and deposit characteristics are critical data used to quantify eruptive material. The homemade ashmeter is a device used to precisely measure thickness, area density, and bulk density of small ash deposits (< 20 mm). This instrument provides both direct measurements in the field and sample collection for laboratory analysis. The primary purpose of this device is to collect fallout from small-volume and distal eruption clouds. The homemade ashmeter is composed of an outer container, a funnel, an inner gauge, and a filter cap, and permits sampling without major weathering effects. It is constructed using mostly recycled materials, thus is very cost effective. To test this system, seven instruments were installed during the January 14 – March 16, 2012 eruption of Tungurahua volcano, Ecuador. The ashmeter allows the measurement and sampling of small tephra falls that can be used to improve fallout hazard assessments.

One of the greatest challenges for explosive ordnance disposal operators is the disarming process of an improvised explosive device. These dangerous devices are often made from homemade explosive. Committing a bomb attack in urban areas is a basic weapon of terrorists, which may claim civilians’ lives. The main aim of experts is to avoid any lethal attack and to stop terrorists who endanger our life. Identifying homemade explosives may also help during the fight against terrorism since information may be provided this way, which is essential for professionals who work in the areas of operations. Usage of high-tech equipment provides stable and reliable background in the field of explosives’ analysis.