Thermal Initiation of Non‐Electric Detonators

Cookoff – the concept of heating explosives to ignition – is a useful tool for determining issues that may be related to safely using and storing explosives, and as such, cookoff experiments have been performed on many different materials. All explosive systems require a means of initiation, which is usually a detonator: a device that often contains a sensitive, primary explosive and a more powerful, secondary explosive. Even if the cookoff behaviors of all the individual explosives in an explosive system are known, the behavior of the combined system may be quite different. In this experiment, the cookoff behavior of non‐electric detonators is investigated. It was determined that there was no distinguishable difference between initiating detonators properly or heating them at a rate greater than 10 °C min⁻¹. Heating detonators at rates less than 10 °C min⁻¹ diminished their output.     

Cast PBX B2238 for Small-Calibre High Performance Insensitive Munitions

Generally speaking, today's small-calibre munitions, filled with conventional melt-cast or pressed high explosives, are classified in the 1.1 or 1.2 Hazard Divisions because they explode when exposed to various threats, such as fuel fire and sympathetic detonation. The RDX-based B2238 composition is a low-cost and less sensitive cast PBX originally developed by SNPE for the initiation of cast PBX main charges. While it is easily initiated with conventional detonators, B2238 offers the same degree of insensitivity as other cast PBXs used for main charges (HEXABU 88A or OCTORANE 86B for example) and does not explode when exposed to fire and/or bullet impact. Feasibility tests carried out on several types of small-calibre munitions have shown B2238 explosive filling to be an excellent solution in the design of small calibre insensitive munitions with a high performance (in terms of fragments and shaped charge jet) comparable to that of the most energetic conventional high explosives such as 98RDX/2wax. As a result, the new IM standards, currently being defined, should allow in the future to reclassify the small-calibre munitions filled with B2238 in Hazard Divisions other than 1.1 and 1.2.     

On AlO Emission Spectroscopy as a Diagnostic in Energetic Materials Testing

The emission of AlO is commonly observed in tests involving aluminum combustion in propellants and explosives. Such emission has been used as a signature of combustion, as a tool for measuring ignition and reaction times, and as a thermometer. This paper provides a critical review of methodologies exploiting AlO emission spectroscopy as a quantitative tool in energetics testing. Controlled tests involving aluminized explosives, as well as those using added alumina, are conducted, in which AlO emission is quantified and compared to total oxidation in the final residue. Experimental parameters such as optical depth and fireball confinement are systematically varied to examine the effect on AlO emission. We find that thermometry using AlO remains valid, and a new approach to using low resolution spectra is proposed. However, AlO emission spectroscopy or photometry can be quantitatively correlated to ignition and burning time, or used to infer the presence or absence of aluminum combustion, only under a limited set of circumstances. Factors that limit the ability to use AlO emission quantitatively are discussed in depth.     

X‐Band Microwave Properties and Ignition Predictions of Neat Explosives

Microwave frequency electromagnetic properties are critical for understanding and predicting the heating and ignition behavior of explosives subjected to microwave irradiation. In this work we report relative complex permittivity measurements in the X‐band (8–12 GHz) for 13 neat explosives measured by the circular cavity technique. This data set was then used in conjunction with COMSOL 4.3 Multiphysics^® finite element analysis software to design and simulate a low power (100 W), high electric field X‐band microwave applicator. The role of the sample holder on our ability to directly study the response of explosives to electromagnetic energy is examined and shown to be critical. Times to ignition were predicted for PETN, TATB, and HMX and indicate that for the proposed applicator and considered properties ignition may occur in less than one second exposure. These predictions show that explosives can be effectively heated in short time scales through direct microwave heating without absorptive binders or inclusions.     

Investigating materials from fires using a test method for spontaneous ignition

The purpose of this study was to utilize the oven test method described in past literature by Bowes to predict the propensity of bulk materials to ignite spontaneously. The results of small‐scale laboratory oven tests were analyzed and compared with large‐scale fire incidents involving several materials in question, including latex examination gloves, residue from an aluminium polishing process, polyurethane purging, and various other plastic products. Where possible, an indication of the role of spontaneous ignition in the fire incidents was identified. Copyright © 2000 John Wiley & Sons, Ltd.     

The Accumulation of Flammable Gases in Cone Calorimeter Tests is Responsible for Flash Ignition of Wool and Cotton Samples

In this paper a possible explanation is presented for the differences found between the fire behaviour of materials in small-scale cone calorimeter tests and the large-scale furniture calorimeter. The results obtained with cone calorimeter/FTIR equipment at 35 kW m⁻² will show that the early flash ignitions of typical materials like cotton and wool are due to the liberation of flammable gases during the pyrolysis phase and the typical ignition situation on the cone calorimeter, that is, the presence of a sparking igniter above the sample. This fast flash ignition and the early heat release behaviour on the cone calorimeter may be in contradiction to the early fire growth in other fire tests where the ignition conditions are clearly different from pyrolysis circumstances, that is, ignition via a burning newspaper, match, gas flame, etc.     

PBX炸药细观结构冲击点火的二维数值模拟

为了研究冲击加载下非均质炸药的点火机理,对PBX炸药细观结构在冲击加载下的响应过程进行了二维数值模拟.首先对炸药颗粒的压制过程进行数值模拟,获得PBX炸药的细观结构模型.然后对炸药冲击点火进行数值模拟计算,考虑了热力耦合作用和炸药自热反应,分析了炸药颗粒尺寸、密度和黏结剂对炸药冲击点火的影响.结果表明,冲击作用下PBX...     

低强度冲击下炸药点火的数值模拟

为了研究炸药在低强度冲击下的反应特性,根据标准的Steven试验建立了数值计算模型,采用热力耦合模型和Arrhenius方程描述炸药的热反应,对不同速度弹头撞击炸药过程进行了数值模拟计算,获得了炸药点火的弹头阈值速度,分析了弹头形状对炸药反应的影响。计算结果表明,在弹头阈值速度下,炸药点火存在一定的延迟时间,随着弹头速度的增大,延迟时间缩短;弹头形状会影响炸药受力过程,使炸药点火特性发生变化。     

Effects of variations in incident heat flux when using cone calorimeter test data for prediction of full‐scale heat release rates of polyurethane foam

The development of methods to predict full‐scale fire behaviour using small‐scale test data is of great interest to the fire community. This study evaluated the ability of one model, originally developed during the European Combustion Behaviour of Upholstered Furniture (CBUF) project, to predict heat release rates. Polyurethane foam specimens were tested in the furniture calorimeter using both centre and edge ignition locations. Input data were obtained using cone calorimeter tests and infrared video‐based flame area measurements. Two particular issues were investigated: how variations in incident heat flux in cone calorimeter tests impact heat release rate predictions, and the ability of the model to predict results for different foam thicknesses. Heat release rate predictions showed good agreement with experimental results, particularly during the growth phase of the fire. The model was more successful in predicting results for edge ignition tests than for centre ignition tests and in predicting results for thinner foams. Results indicated that because of sensitivity of the burning behaviour to foam specimen geometry and ignition location, a single incident heat flux could not be specified for generating input for the CBUF model. Potential methods to determine appropriate cone calorimeter input for various geometries and ignition locations are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

The Development and Application of a Pivoted Beam Test Apparatus for Assessing Safety in the Handling of Initiator Devices

Initiator devices contain small quantities of explosives and are therefore capable of causing harm to operators in the event of an accidental initiation. Little information exists on methods for assessing whether initiator devices can be safely subjected to the sorts of forces generated in manual handling. We have therefore undertaken research to quantify such forces and then to design the apparatus to replicate them. Typical forces are those generated in pulp pinch grips and in single finger presses. This paper presents information relating to the design and use of a pivoted beam unit and its use to investigate percussion caps, a conducting composition cap, stab detonators, flash sensitive detonators, electric detonators and stab igniters.     

A laboratory-scale gallery fire test on rubber conveyor belts with fabric skeletons

The authors have conducted a laboratory-scale gallery fire test on nine different rubber conveyor belts with fabric skeletons. The interior of the gallery used in this test was 2.5 m long, 0.35 m wide and 0.35 m high. The fire test on each sample was conducted in the upward airflow of the inclined gallery as well as in the horizontal one, and both 60 mm and 90 mm wide specimens, whose length was about 1.5 m, were provided for each test. The test results were compared with those from some other small-scale flammability tests; i.e. the small-scale flame, the oxygen index and the hot plate ignition tests. In addition, some problems in the laboratory-scale gallery fire test were also discussed. As a result, it has been found empirically that determination of both the time to ignition and the flame-propagation speed could be significant in case the flame propagated over the whole length of the belt specimen in the gallery, so that the fire resistance of the belt samples could be classified in detail.     

Fire risks of burning asphalt

Eyewitnesses describe burning pavement surfaces in extreme fire scenarios. However, it was believed that the pavement plays a negligible role in comparison to other items feeding such an extreme fire at the same time. The asphalt mixtures used differ widely, thus raising the question as to whether this conclusion holds for all kinds of such materials. Three different kinds of asphalt mixtures were investigated with the aim of benchmarking the fire risks. Cone calorimeter tests are performed at an irradiance of 70kWm^?2. All three investigated asphalts burn in extreme fire scenarios. The fire response (fire load, time to ignition, maximum heat release rate and smoke production) is quite different and varies by factors of up to 10 when compared to each other. The fire load per mass is always very low due to the high content of inert minerals, whereas the effective heat of combustion of the volatiles is quite typical of non‐flame retarded organics. The heat release rate and fire growth indices are strongly dependent on the fire residue and thus the kind of mineral filler used. Comparing with polymeric materials, the investigated Mastic Asphalt and Stone Mastic Asphalt may be called intrinsically flame resistant, whereas the investigated Special Asphalt showed a pronouncedly greater fire risk with respect to causing fire growth and smoke. Thus the question is raised as to whether the use of certain kinds of asphalts in tunnels must be reconsidered. Apart from the binder used, the study also indicates varying the kind of aggregate as a possible route to eliminate the problem. Copyright © 2010 John Wiley & Sons, Ltd.     

Fire and upholstered furniture

Both ignition and rate of fire development tests are required to determine the fire performance of upholstered composites. Current practice uses small-model specimens for ignitability tests but rate of burning tests are usually carried out on actual furniture. This paper discuss small- and large-scale tests for upholstered furniture.     

Performance and failure mechanism of fire barriers in full-scale chair mock-ups

The effectiveness and the failure mechanism of fire barriers in a residential upholstered furniture (RUF) were investigated by full-scale flaming tests on upholstered chair mock-ups. Six commercial fire barriers were tested in this study. Fire barriers were screened for the presence of elements that are typically used in fire retardants and the presence of commonly used fire retardants. For each fire barrier, triplicate flammability tests were run on chair mock-ups, where polyurethane foam and polyester fiber fill were used as the padding materials, and each chair component was fully wrapped with the fire barrier of choice and a polypropylene cover fabric. The ignition source was an 18 kW square propane burner, impinging on the top surface of the seat cushion for 80 seconds. Results showed all six fire barriers reduced the peak heat release rate (as much as ≈64%) and delayed its occurrence (up to ≈19 minutes) as compared to the control chair mock-ups. The heat release rate remained at a relatively low plateau level until liquid products (generated by either melting or pyrolysis of the padding material) percolated through the fire barrier at the bottom of the seat cushion and ignited, while the fire barrier was presumably intact. The flaming liquid products dripped and quickly formed a pool fire under the chair, and the peak heat release rate occurred shortly thereafter. Ultimately, the ignition of the percolating liquid products at the bottom of the seat cushion was identified as the mechanism triggering the failure of the fire barrier.     

Experimental investigation into the influence of ignition location on flame spread and heat release rates of polyurethane foam slabs

This study presents the results from a set of 11 large‐scale open fire tests performed on flexible polyurethane foam slabs/mattresses. The purpose of the study was to investigate the influence of the ignition location on the fire behaviour of the foam slabs and to generate data on a highly characterised material that could be used for modelling work in the future. A method for obtaining spatially resolved flame spread data for this type of material was presented using a gridded array of 5 × 10 thermocouples placed on the underside the foam slab and from this, flame spread was examined using three different approaches. The heat release rate (HRR) results showed clear shapes forming that were dependent on the ignition location, with two distinct behaviours being observed between the various different ignition locations, this was also observed in the calculated flame spread rate (FSR) data. Results within an individual test, showed the calculated range of FSRs over the geometry of the slab varied between approximately 1 and 8 mm/s depending on the ignition location. The average FSR values between tests varied between 3 and 7 mm/s and the maximum and minimum values were calculated to be approximately 11 and 2 mm/s respectively.     

High Safety and Reliability Electric Detonator

The entry into force of the REACH regulation implies a modification of the low‐cost detonators manufacturing by finding new substances to replace common primary explosives that contain restricted chemicals. Herein, an alternative solution with a two‐stage electric detonator that contains only secondary high explosive is proposed. It is based on a two steps process, first a combustion, then a shock to detonation transition. This initiator shows high safety level and is compliant with the STANAGs and the REACH regulation. Contrarily to the EBW detonators, it can be initiated using low voltage and low current. Power supply system can be therefore very compact that is of great advantage for designing pyrotechnical train that have to be integrated into small pyrotechnical mechanisms.     

A simplified model for predicting the ignition of FRP composites with validation using intermediate‐scale fire experiment data

This study presents a simplified theoretical model to predict the ignition of FRP composites of general thermal thickness (GTT) subjected to one‐sided heating. A simplified GTT heat transfer model to predict the surface temperature of GTT composite panels was developed, and the exposed surface temperature was used as ignition criterion. To validate the GTT model, intermediate scale calorimeter fire tests of E‐glass fiber reinforced polyester composite panels at three heat flux levels were performed to obtain intermediate‐scale fire testing data in a controlled condition with well‐defined thermal boundary conditions. The GTT model was also verified by using results from finite element modeling predictions. This model can be used to estimate the surface temperature increase, time‐to‐ignition, and mass loss of FRP composites for fire safety design and analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Bedding ignition,vertical flame spread and subsequent thermal impact on underlying mattress

The ignition of bedding and subsequent vertical spread of fire along the side of a noncombustible surrogate bed set was investigated. One‐hundred‐eight (108) tests were conducted to assess the ignition timeline and subsequent vertical flame spread of bedding up the side of a bed along with the thermal impact of the bedding fire on the underlying bed set. The ignition source for all tests was comprised of the flame from a book of matches placed on bedding at floor level at the base of the bed. The bedding consisted of combinations of a cotton/polyester blend sheet and bedspread. Ignition occurred in 3 to 10 seconds for the majority of the test. The speed of subsequent vertical flame spread, assessed through video frame analysis tools, was dependent on the exposed bedding material with an exposed sheet exhibiting faster spread. Thermal exposure from the burning bedding to the vertical sides of the bed set was assessed with an array of thermocouples embedded at the surface of the sides of the underlying bed set. The time to thermal exposure was found to be a function of the vertical flame spread and thickness of the bedding material(s).     

Electrostatic Discharge Ignition of Energetic Materials

Electrostatic discharge(ESD) ignition of explosives, pyrotechnics, or propellants is often considered to be mainly dependent upon various physical characteristics of the energetic material. This work shows that ESD ignition of secondary explosives tested in powdered form is primarily dependent upon the chemical characteristics of the energetic material(i.e., the decomposition rate kinetics of the materials). We propose that ignition occurs when a spark raises the temperature of the explosive particles to the point where thermal runaway occurs. ESD sensitivities of a diverse series of explosives were measured using a traveling needle test apparatus with the powders slightly confined by Mylar tape to prevent formation and ignition of a dust cloud. Using global thermal decomposition rate coefficient expressions, two parameters were calculated for each explosive:(1) the critical temperatures according to the Frank-Kamenetskii formula for 20 μm particles of each explosive and(2) the temperatures at which the rate coefficient equaled 10³ s⁻¹. These two sets of data were correlated with the observed ESD sensitivities for 50 percent probability of ignition, E₅₀. Excellent correlations resulted, indicating that for ESD ignition under these conditions the spark discharge is primarily a thermal source.