Explosives residue analysis in the mid-1980's–an expanding and challenging role for the forensic scientist

The Forensic Scientist who undertakes explosives residue analysis in the 1980's must not only be a skilled analyst, but also a skilled student, educator and consultant. The subject is multi-disciplinary, the scope is international, and the keywords are ‘‘experimentation'’ and ‘‘communication''. This paper expands on each area, drawing illustrations from recent Canadian experience which includes visits to major Forensic Laboratories on three continents. Specific emphasis is given to reviewing current literature on explosives analysis and considering the criteria which must be met by a new method in order for the Forensic Scientist to add it to his routine scheme for systematic analysis of explosives residues.     

Molotov cocktails and similar devices used by terrorists in israel

During the last few years there has been a great increase in the use of home-made improvised explosives and combustible materials by terrorists in Israel. The most common device is a bottle containing an inflammable liquid and an ignition mechanism. We define such a bottle (often called a ‘‘Molotov Cocktail'') as an ‘‘incendiary bottle''. The composition of the inflammable liquid is determined by our laboratory and each of its components identified. The results serve as court evidence as well as to connect between cases during the investigation. In this paper several examples of incendiary bottles encountered recently by our laboratory are described.     

The behaviour of non-ideal explosives in the Ballistic Mortar

Abstract

An analysis has been developed for the Ballistic Mortar test based on classical mechanics and a two stage chemical reaction rate model. Non-ideal behaviour of the composition was modelled by partial energy release during the detonation phase and secondary exothermic processes during the expansion phase. Erosive grain burning and time delayed reactions were both considered. Gas loss from the mortar cavity due to leakage was included. Predicted mortar performance of several ideal and non-ideal explosives were in good agreement with experimental values. The effects of slow and incomplete reaction of non-ideal compositions have been demonstrated, and it has been shown that measurement of mortar throw angle alone is insufficient to determine the performance of a composition. The model has been used to elucidate the reaction rate behaviour of Ammonium Nitrate and Aluminium in commercial explosives.     

Laser ignition of explosives: Effects of laser wavelength on the threshold ignition energy

Abstract

A method, based on a tunable 180 W CW CO₂-laser (9–11 μm), for measuring the effect of laser wavelength, and hence optical absorbance coefficient, on the threshold ignition energy of explosives, has been developed. To determine how the laser beam interacts with the high explosives, a theory for the connection between the ignition energy and the optical absorption coefficient is formulated. The dependence of the threshold ignition energy of RDX on laser wavelength, and hence on the optical absorption coefficients for RDX, was studied at two pressures: 1.1 and 3.1 MPa. In this wavelength interval (9–11 μm), the ignition energy varied between 30 and 330 mJ for a beam radius of 0.9 mm and at a pulse width of ≈ 4ms. At wavelengths with large optical absorption depth (25–60 μm), the ignition energy was the same for both pressures, while at wavelengths with small optical absorption depth (< 15 μm), the ignition energy was much higher at 1.1 MPa than at 3.1 MPa. This behavior is discussed in detail, and a number of sub-processes taking part in the complete ignition process are identified: 1) Lambert-Beer absorption in the solid phase leading to a decomposition of the HE into gaseous products. 2) At low pressure, the gaseous decomposition products can absorb a portion of the laser energy leading to a lowering of the laser energy deposited in the high explosives, and hence a higher ignition energy. 3) At high pressure, the gaseous reaction products are collapsed onto the sample surface. 4) At large optical absorption depths (>25 μm), a large volume of explosive is heated, ‘‘confining'’the decomposition, and thus lowering the ignition energy.     

A novel method for prediction of the critical diameter of solid pure and composite high explosives to assess their explosion safety in an industrial setting

ABSTRACT

For the explosion safety assessment in an industrial setting, the knowledge of critical diameter of high explosives provides important information on the sensitivity and conditions whereby detonations are likely to occur. The critical diameter or failure diameter is the minimum diameter of a cylindrical charge of high explosive which sustains a high order steady-state detonation. Available predictive methods require complex models, which are based on complicated variables such as the shock adiabat, and the generalized kinetic characteristic of decomposition of a high-explosive charge under shock-wave compression. For the first time, this paper describes a novel simple method for assessment of the critical diameter of pure and composite CHNO high explosives. The new model is based on the contribution of the number of nitrogen and oxygen atoms as well as some conditions, which are based on shock sensitivity, impact sensitivity and the negative values for core critical diameter of the desired explosives under certain situations. Experimental data of 42 high explosives have been used to derive and test the new model. The predicted critical diameters for building the model (29 explosives) and the test set (13 explosives), under the unconfined condition of these explosives, have the values of root-mean-square deviation (RMSD) of 5.14 and 3.96 mm, respectively.     

Formation and structure of axisymmetric steady-state detonation mach stems in condensed explosives

High explosive detonation mach stem phenomena is a relatively new research area which has been studied only since the early 1960's. Although non-steady mach stems in gases have been studied extensively, steady state mach stems have been largely ignored, particularly in high explosives. None the less, steady state detonation mach stems are of great interest due to the observability of continuous highly overdriven detonations. In order to gain a better understanding of axisymmetric steady mach stem formation and structure in high explosives, two dimensional dynamic Lagrangian numerical simulation was done. The results are presented, along with experimental evidence that confirms the validity of the calculations.     

Detonation Characteristics of Plastic Explosives Based on Attractive Nitramines with Polyisobutylene and Poly(methyl methacrylate) Binders

Four highly brisant nitramines, RDX (1,3,5-trinitro-1,3,5-triazinane), HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane), BCHMX (cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole), and ?-HNIW (?-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane), were studied as extruded plastic explosives bonded by two plastic matrices based on polyisobutylene (C4 matrix) and poly-methylmethacrylate (plasticized by dioctyl-adipate) binders. The detonation velocities, D, were measured experimentally. Detonation parameters were also calculated by means of the Kamlet and Jacobs method and CHEETAH and EXPLO5 codes. These detonation parameters showed that plastic-bonded explosives (PBXs) based on BCHMX are more powerful explosives than those based on RDX. The Urizar coefficient for poly(methyl methacrylate) binder was also calculated.     

Numerical study of countermeasure against thermal stimuli for HMX-based polymer-bonded explosives

ABSTRACT

An accurate thermal decomposition model of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based polymer-bonded explosives is indispensable to the design of countermeasure against environmental thermal stimuli for certain explosive devices. However, the complicated chemical reactions occurring in decomposition of HMX-based polymer-bonded explosives pose great challenge to scientists. In this study, the thermal ignition kinetic model proposed by Tarver is implemented to study thermal decomposition of HMX-based polymer-bonded explosives using commercial software Abaqus, which does not only consider the thermal decomposition of HMX but also the polymer binders. The simulation results are compared to ODTX and Scaled Thermal Explosion Experiment (STEX) and reasonably good agreements are achieved. Then the thermal decomposition model is applied to analyze an explosive device exposed to environmental thermal stimuli. Furthermore, countermeasure against environmental thermal stimuli is suggested and analyzed quantitatively for the explosive device. The time to explosion and environmental temperature before ignition is calculated and analyzed for the explosive device under various heating rates.     

Liquid chromatography with photolysis–electrochemical detection for nitro-based high explosives and water gel formulation sensitizers

The use of high performance liquid chromatography with photolysis–electrochemical detection (LC-hv-EC) for conventional high explosives has been improved through the use of a knitted open tubular (KOT) photolysis chamber geometry. Improvements in the analytical figures of merit and selectivity of this hybrid analytical technique are a direct result of the improved radial mass transfer of analyte in the KOT reactor, as demonstrated in comparisons with the coiled reactor geometry previously used. Using the KOT photolysis chamber geometry in LC-hv-EC, the limits of detection for aromatic C-nitro compounds, nitramines and nitrate esters are in the range of 120- to 250- pg injected. In addition, an off-line, pre-column chemical derivatization has been developed to convert water gel sensitizer residues to a form which will allow for their determination using LC-hv-EC. In a rapid, single-step process, 2,4-dinitrofluorobenzene (Sanger's reagent) is used to derivatize residues of monomethylamine and monoethanolamine to their 2,4-dinitrophenyl analogues. Under the preliminary conditions reported here, monomethylamine may be quantitatively converted and detected at concentrations between 200-parts per billion and 50-parts per million. Monoethanolamine is detected with-about 35% derivatization efficiency at levels between 10- and 200-parts per million. The preliminary results suggest that this methodology may be easily improved to allow for the trace determination of water gel sensitizers in aqueous extracts of post-blast debris.     

Development of risk assessment techniques for use in the field of explosives and ammunition

Abstract

Criteria for estimating the risks involved with ammunition and explosives are presented against a background of the public's perception of risk. The criteria are presented in terms of a three band approach separated by two threshold risk levels. The upper and lower bands represent unacceptable and trivial risk situations respectively, whilst the middle band represents a region in which the risk levels must be reduced to as low a level as is reasonably practicable.

Individual Risk criteria are presented for three groups of people: the workforce necessarily exposed to risk in the course of their daily work, those members of the workforce who do not need to be exposed to risk in order to do their work and the general public. In the case of Societal Risk only one set of criteria are presented on the basis that when a major incident involving large numbers of casualties occurs the public reaction does not discriminate in its perception of horror between members of the general public and members of the workforce. In addition to preserving life it is suggested that criteria are required to preserve stocks in situations where life itself may not be at risk. For this it is recommended that the propagation of initial initiation or explosion to other munitions nearby by sympathetic detonation should be prevented, as far as possible, by the maintenance of the current separation distances for magazines, updated where necessary as new knowledge becomes available and new explosives and munitions are developed.

The present tentative proposals are compared with quantitative risk evaluation criteria proposed in other countries and in other industries.     

The influence of temperature on the detonation velocity of selected emulsion explosives

ABSTRACT

Many years of research on more effective and safer explosives led to the development of emulsion explosives. They are the second most commonly used group of explosives in the world, primarily due to the fact that they are a good alternative to ANFO explosives or dynamites. Their key advantage in underground applications is the lower content of toxic fumes in the detonation products. Emulsions are also characterized by high detonation velocity, high water resistance, low value of critical diameter and mechanical loading capacity. Multiple factors related to the applied mining method influence the detonation parameters of emulsion explosives. One such parameter is the time between the loading of the explosive into the blast hole and firing, which in the case of underground copper mines in Poland can even last up to 48 hours. This becomes a particularly significant issue due to the increasing depth of mining in Polish copper mines and the high virgin temperature of rock mass at these depths. Experiences related to the use of explosives and their efficiency under such conditions confirm the intuitive thesis that high ambient temperature has a negative impact on the explosives’ effectiveness. In this regard, research concerning the influence of temperature on the detonation velocity of selected emulsion explosives was carried out, including bulk and packaged explosives. The tests were performed for different conditioning temperatures, which are all locally observed in Polish copper mines. The obtained results confirmed the significant influence of temperature on the velocity of detonation of the considered explosives.     

Numerical analysis of response of a fuze to cook-off

ABSTRACT

A fuze may be exposed to extreme thermal environments during its life cycle, such as high temperature resulting from burning of leaked fuel, or accidental deflagration (or explosion) of shells. It is essential to study the response of fuzes under cook-off conditions to reduce possible economic loss and casualties. Cook-off tests are an important experimental method to test and evaluate the thermal sensitivity of shells and fuzes at present, and extensive research has been done on the subject. However, it is not economical to conduct many experiments in the early stage of product development due to high cost and risk. Herein, numerical simulations are conducted to analyze the response of a fuze to cook-off. Thermal-decomposition models for HMX- and TATB-based polymer-bonded explosives proposed by Tarver are applied in the numerical models. In addition, the influence of various factors on simulation results, such as heating rate, package of the fuze, type of high explosives within the fuze is analyzed quantitatively. The law is summarized and can be used for future development of similar products.     

Transport and preconcentration of explosives vapors by liquid sampling modules

For most explosives vapor detection scenarios, the lower detection limit (LDL) requirements are at part-per-trillion (ppt) concentration levels. Further sensitivity constraints are imposed on the detector modules by attendant sampling dilution and inefficient transport of explosives vapor molecules through the detection system sample train. Efficient transport and large preconcentration factors (? 100,000) can be achieved simultaneously by using a liquid sampling module, comprising a wetted-wall column in the sample train. Liquid sampling modules are interfaced most effectively to wet-chemical detectors. The transport and preconcentration processor introduces a 60-s or longer lag to the overall system time rate-of-response depending on the preconcentration requirements. Despite the long delay time of liquid preconcentrators and the relatively slow rate-of-response time and limited sensitivity of wet-chemical vapor detectors, it appears that their use is feasible for some applications. For example, those detectors with a liquid transport and preconcentration sample train can monitor the atmosphere within enclosures such as rooms, buildings, etc. The inlet to the sample can be located at some convenient and effective point, e.g., in the main air conditioning or ventilation duct upstream of the blower.

An explosives vapor detection system comprising a liquid sampling module and a wet-chemical detector and their ancillary equipment can be an effective device for some applications. Integration of a liquid sampling module into a system can extend the LDL of an enzymatic bioluminescent TNT detection technique to an equivalent 0.001 ppt gas phase concentration. It is accomplished by the extraordinary sample preparation achieved by a liquid sampling module in the form of efficient sample transport and sample concentration.

Currently two liquid sampling modules for vapor detection systems are in development by the U.S. Army. Fort Belvoir is developing Spincon: a batch-type sampling module for an explosives detection system employing an enzymatic bioluminescent technique. The Aberdeen Proving Ground is developing BezeTrog: a continuous liquid sampling module for the detection of hazardous waste gas molecules in the flue streams employing a coloriometric technique.

A liquid sampling module is used as an end-line device interfacing directly with the detector. It contributes significantly to the detection system's performance in meeting the very stringent requirements imposed on explosives vapor detection systems. Although a liquid sampling module fits easily into the general scheme of a typical vapor detection network its design and implementation is a major engineering undertaking.     

On predicting properties of explosives – detonation velocity

Abstract

A systematic method of representing an explosive, based on its composition, is presented. This method is used to display performance data for existing explosives, and suggests an alternate definition for oxygen balance and determines compositions that might produce high-performance explosives. A new method for predicting the detonation velocity of a proposed explosive is also presented. This is a simple method that also yields insight into which factors are important in predicting performance.     

The application of neural networks to the assessment of impact testing on explosives

Abstract

The BAM Fallhammer test is one of the most widely used impact tests, but the results of the test rely on the subjective assessments of the test operator using the senses of hearing, smell and sight. The paper describes an investigation into the suitability of using a neural network for determining the outcome of BAM Fallhammer tests. The network utilises digital data from instrumentation installed around the BAM apparatus, including a microphone and a gas sensor.

Selected examples are given to show that neural networks have the potential to distinguish between the test results of ‘no reaction’, ‘decomposition’, and ‘explosion’ for propellants, plastic and high explosives. The technique removes the possible operator dependence of assessments and the study in general may also lead to clarification of the categories involved in defining the test outcome.     

A study on dynamic compressive properties of energetic materials at low temperature

Abstract

The mechanical response of explosives at low temperature was investigated and an experiment apparatus is presented which is available to conduct dynamic compression for explosives at low temperature. Measurements of Comp. B and TNT explosives have been made. The data obtained experimentally depend greatly on the strain rate employed. It is found that the strain ε_m (ε_m is the strain at compressive strength σ_m) increased with increasing strain rate for both explosives at low temperature. The mechanical properties of Comp. B are higher than those of TNT for all measuring conditions in the present study. The effect of inertia on experiment curves was reduced by introducing a factor of flexibility.     

Shock initiation of TATB/FEFO formulations

Abstract

The shock initiation properties of transferable insensitive explosive (TIE) formulations based on the solid high explosive, triaminotrinitrobenzene (TATB), and the liquid explosive, bis(2-fluoro-2,2-dinitroethyl) formal (FEFO), are measured by wedge test, embedded particle velocity gauge and embedded manganin pressure gauge techniques and calculated using the Ignition and Growth reactive flow model. These extrudable formulations are demonstrated to be slightly more shock sensitive than the TATB/inert binder explosive, LX-17. However, the TIE formulations are much less sensitive than HMX-based explosives and still qualify as insensitive explosives in safety and hazard tests. The wedge tests showed a very steep dependence of run distance to detonation on the input shock pressure. Embedded gauge and reactive flow modeling results imply that shock initiation begins when a small amount of the solid TATB decomposes rapidly enough to heat the surrounding FEFO to decomposition temperature. The FEFO then reacts rapidly, raising the pressure and temperature sufficiently to cause surface decomposition of the TATB particles at rates comparable to those measured in other TATB-based explosives. An Ignition and Growth reactive flow model for TIE based on these assumptions yields reasonable agreement with the experimental shock initiation data.     

Laser ignition of explosives: Effects of gas pressure on the threshold ignition energy

Abstract

This paper describes a method for measuring the effect of initial gas pressure and the type of gas on the threshold ignition energy of several high explosives. The method is based on a 300 W CW CO₂-laser. An extensive study of these parameters for PETN and RDX is also presented. These high explosives all show a strong decrease in ignition energy/power with increasing initial gas pressure. The gases tested are air and nitrogen. The studied pressures are in the interval 0.1 to 10 MPa. The ignitability of PETN and RDX was tested at a laser pulse width of 1.2 ms. All tested high explosives had a lower ignition energy/power in air than in nitrogen at low pressures (< 2 MPa), whereas RDX and PETN had a lower ignition energy in nitrogen than in air at high pressures (>4 MPa). For TNT the time to ignition, measured as a function of air pressure, decreased with increasing pressure. These results are interpreted as a multiple phase ignition process. The method was also used for obtaining ignition data for TNT, Comp B-3 and Torpex.     

低渗透油气田“层内爆炸”增产技术研究

回顾爆炸法(井内爆炸法、核爆炸法和高能气体压裂)增产油气的历史,提出低渗透油气田“层内爆炸”增产技术的基本思路利用水力压裂技术将乳胶状爆燃药压入油层裂缝,并采取不损毁井筒的技术措施点燃该爆燃药,从而在水力压裂主裂缝邻域造成碎裂带,达到提高采收率、增产原油的目的。至少已找到一组特种火炸药基本配方,在200mm小尺度模拟实验中实现了“层内爆炸”挤注、点火和爆燃的过程,证实技术原理基本可行。考虑流体内部的热传导、边界的热损失和阻尼,提出了有化学反应的薄层药爆燃一维可压缩流体力学模型,并对此模型进行恒稳推进和不可压缩简化,计算结果的物理图象符合常理,从理论上证实了薄层药爆燃可行。“层内爆炸”油井产出液的后处理,原则上是安全的残留在岩缝的未爆炸炸药颗粒在生产阶段难以流出地层;进入集输系统的残药颗粒浓度低于1%,原则上能用离心法分离;残留在分离后原油中的的微量炸药在400℃加热炉已完全热分解,热分解不可能导致爆炸。“层内爆炸”增产技术的研究是具有战略性、前瞻性的科技创新课题,预期增产效益显著高于水力压裂,有可能形成低渗透油气田开采的新局面,还可能使一些目前不可采的低渗透油气资源成为可采资源。今后工作主要有四方面室内放大试验与相关理论研究;安全技术研究;现场试验用工艺设备研制;现场井下试验。图2表6参9(王孝陵摘)     

Composition Choice and Formulation of Three HMX-Based Research Explosives

The composition and formulation for three research explosives having similarities to military explosives are described. The primary energetic ingredient in each is cyclotetramethylene-tetranitramine (HMX), whose particle size is limited to a range of 125–210 μm to reduce variations in shock reactivity and performance. The binder in each explosive is hydroxy-terminated polybutadiene (HTPB). The first composition contains only these two components. Aluminum with a nominal particle size of 5 μm is incorporated into the second composition. The third composition contains ammonium perchlorate (AP) with a nominal particle size of 200 μm in addition to the aluminum. The explosives are designed with features to allow for comparisons in shock reactivity and performance and to elucidate the roles of HMX, Al, and AP.