AU2013202120B2 - Device for improved method of blasting - Google Patents

Abstract

H:\KXG\Interwoven\NRPortbl\DCC\KXG\5025707_ .doc-27/03/203 An explosive cartridge comprising: an explosive composition; a deactivating agent that is capable of desensitising the explosive composition; and a barrier element that prevents contact between the explosive composition and the deactivating agent and that is adapted to be at least partially removed on use of the explosive cartridge.

Description

H:\kxg\Intenvoven\NRPortbl\DCC\KXG\5412077-1.doc-23/09/2013 DEVICE FOR IMPROVED METHOD OF BLASTING This is a divisional of Australian Patent Application No. 2009208388, the entire contents of which are incorporated herein by reference. 5 The present invention relates to a cartridge that contains an explosive composition and that is adapted to achieve deactivation of the explosive composition in the event that it is not detonated as intended during use. 10 Explosives are used in a significant number of commercial applications, such as mining, quarrying and seismic exploration. In mining and quarrying a detonator is typically used to initiate a cartridged primer charge that in turn detonates bulk explosive. In seismic exploration a relatively small cartridged explosive charge is initiated using a detonator and the shock waves that are generated are monitored and analysed. 15 When a charge fails to detonate as intended there are obvious safety and security issues. In that event, it may be possible to recover the charge, although this is not always possible for a variety of reasons. For example, in seismic exploration where charges or trains of charges are positioned and detonated, recovery of undetonated charges can be difficult, 20 especially when the charge(s) is/are positioned in an underground borehole and the borehole has been backfilled, as is common practice. There are therefore instances where undetonated charges remain unrecovered in the field. In such cases, and as a general point, it would therefore be desirable to render safe any undetonated and unrecovered explosive charges. A variety of approaches to address this need already exist. 25 By way of example, US 3,948,177, describes an explosive cartridge for underwater blasting which is said to be self-disarming in the event of an underwater misfire. The cartridge comprises a closed shell including an internal conduit. Water external to the cartridge is prevented from flowing into the conduit by a watertight seal. The force of a 30 percussion impact initiation can however break the watertight seal thereby allowing water to flow into the conduit and contact with explosive composition contained. In turn, water H:\kxg\Intenvoven\NRPortbl\DCC\KXG\5412077 L.doc-23/09/2013 -2 can dissolve the (nitrocarbonate) explosive possibly also causing it to flow out of the body of the cartridge. The result is desensitisation. Whilst generally useful, a problem with this approach is that desensitisation is contingent upon some form of specific force associated with a misfire to break the watertight seal. If there is no applied force resulting from a 5 misfire, the cartridge would not be disarmed by the action of water. The present invention seeks to provide an alternative approach to rendering safe explosive compositions that does not suffer the disadvantages described above. 10 In an embodiment the present invention provides an explosive cartridge comprising: an explosive composition; a deactivating agent that is capable of desensitising the explosive composition; and a barrier element that prevents contact between the explosive composition and the deactivating agent and that is adapted to be at least partially removed on use of the explosive cartridge, wherein the barrier element takes the form of flexible 15 membrane attached to a support member, the support member being resiliently extendable between a retracted position in which the flexible membrane does not prevent contact between the deactivating agent and the explosive composition and an extended position in which the flexible membrane prevents contact between the deactivating agent and the explosive composition, one end of the support member being attached to an internal wall 20 of the explosive cartridge and the other end of the support member being attached in the extended position to a release mechanism, wherein the release mechanism prevents movement of the support member between extended and retracted positions for a predetermined period of time. 25 In accordance with the present invention, the action of a deactivating agent on the explosive composition is responsible for rendering the explosive composition insensitive to detonation, i.e. safe. Herein, unless otherwise evident, when it is indicated that an explosive composition is rendered insensitive to detonation means that the explosive composition has, by action of the deactivating agent, been desensitised at least to the extent 30 that the normal (predetermined) method of initiation of the explosive composition is no longer effective. Thus, for an explosive composition that is known to be detonated using a H:\kxg\lntenvoven\NRPortbl\DCC\KXG\5412077_ 1. doc-23/09/2013 -3 particular type of initiating device, in accordance with the present invention the explosive charge is rendered insensitive to detonation if it is no longer possible for it to be initiated in that way. The fact that an explosive composition has been rendered insensitive to detonation does not mean that the explosive charge is completely undetonable (although 5 this is of course a possibility). At the very least, the extent of desensitisation effected by the deactivating agent in accordance with the invention results in the explosive composition being insensitive to the initiation means that was otherwise and originally intended to cause detonation of the explosive composition. 10 In an embodiment of the present invention it may be desirable to employ two different deactivating agents (i.e. with different activities) to effect desensitisation of the explosive composition. In this case one of the desensitising agents acts to degrade the explosive composition to some by-product, with the other deactivating agent acting on the by product. The latter deactivating agent has the effect of thermodynamically increasing the 15 efficiency of the first deactivating agent due to degradation of the by-product associated with the deactivating activity of the first deactivating agent on the explosive composition. This embodiment may be implemented with more than two deactivating agents, as appropriate. In this embodiment at least one deactivating agent should be as required in accordance with the present invention. The other deactivating agent(s) may be of the same 20 or different type. Typically, the deactivating agent will itself cause suitable desensitisation of the explosive composition. However, it is also possible that desensitisation may be achieved through the combined activity of the deactivation agent and a reagent external to the explosive 25 cartridge that will find its way or be introduced into the cartridge during use thereof and that can contribute to desensitisation of the explosive composition. Such reagents may be naturally present in the environment in which the explosive cartridge is to be used. In this embodiment the explosive cartridge will be adapted to allow the relevant reagent to be introduced into or enter the explosive cartridge as required. 30 H:\kxg\Intenvoven\NRPoNbl\DCC\KXG\5412077_ 1.doc-23/09/2013 -4 In this case the relative order of activity of the deactivating agent and the another reagent is not especially critical. For example, the another reagent may degrade the explosive composition into a particular by-product that is then acted upon (degraded) by the deactivating agent, or vice versa. In this case the combined activity of the agent and 5 reagent give a beneficial effect in terms of reaction thermodynamics. Of course, the deactivating agent and another reagent may have the same general activity with respect to the explosive composition. In this case other reagents may be employed to enhance the thermodynamics of the relevant reaction(s) by consuming reaction(s) by 10 products. By way of example, in certain embodiments of the invention, the explosive cartridge may be designed to allow environmental water to enter the body of the cartridge and contact the explosive composition, assuming of course that water has a desensitising effect of the 15 emulsion. By way of further example, the cartridge may be adapted to allow ingress of microorganisms, for example water-borne microorganisms, that exist naturally in the environment in which the explosive cartridge is being used and that are capable of remediating the explosive composition contained in the cartridge. The cartridge may be provided with a nutrient source to promote uptake and proliferation of such 20 microorganisms. In accordance with the invention in the explosive cartridge the deactivating agent and explosive composition are initially separated by a barrier element that prevents contact of these species. Central to the present invention is the use of a barrier element that is 25 employed. Prior to use of the explosive cartridge, that is positioning and priming of the explosive cartridge, the barrier element prevents contact between the deactivation agent and explosive composition. The barrier element remains in place between the deactivating agent and explosive composition when the explosive cartridge is actually positioned and primed but some mechanism for delayed removal of the barrier element is activated. 30 H:\kxg\Intenvoven\NRPortbl\DCC\KXG\5412077_ .doc-23/09/2013 -5 Typically, the external configuration of the explosive cartridge is cylindrical with the deactivating agent and explosive composition occupying respective chambers within the body of the cartridge. In this embodiment the explosive cartridge is sealed so that there is no risk of escape of components, for example, during storage and/or transportation. 5 Sealing may be achieved by conventional techniques depending upon the materials used to form the cartridge. If the cartridge is formed from plastic, the body of the cartridge, including the respective chambers of it, may be formed by injection moulding with the chambers of the cartridge being loaded with the deactivating agent and explosive composition as required, with subsequent sealing (heat sealing, for example) in order to 10 seal the inlets through which these components are supplied into respective chambers in the body of the cartridge. As an alternative, rather than relying on separate chambers that are integrally formed as parts of the cartridge structure, the deactivating agent and/or explosive composition may be provided in independent containers that are inserted into a rigid cartridge body. In this case it will be appreciated that the cartridge is made up of at 15 least two independent parts and that in use the cartridge is assembled from those parts. The material(s) used to form the cartridge of the invention should not be corroded by or be reactive towards the deactivating agent and explosive composition to be contained. Thus, the cartridge will retain its structural integrity. 20 With respect to use of a detonator, the cartridge is usually adapted to receive the detonator in a suitably shaped passage extended axially within the body of the cartridge. The integrity of the barrier element will only be compromised when the detonator is being 25 used in the field. Prior to that point in time the barrier element is intended to remain intact thereby separating the deactivating agent and explosive composition. In accordance with the present invention the barrier element is adapted/designed to be breached or removed only after the explosive cartridge is used. Removal/breach of the 30 barrier element is not instantaneous on use of the cartridge, but rather some mechanism is activated that will lead to removal/breach of the barrier element after some predetermined H:\kxg\Intevoven\NRPotbl\DCC\KXG\5412077_1-doc-23/09/2013 -6 period of time. Taking into account the activity of the deactivating agent this will invariably be a period of time after which desensitisation of the explosive composition is desired due to failure of the explosive cartridge to be detonated, as described above. The mechanism by which the barrier element is removed or breached may be chemical, 5 electrical or mechanical in character. In accordance with the invention the mechanism that is activated to cause breach/removal of the barrier element is mechanical in nature. Specifically, the barrier element takes the form of flexible membrane attached to a support member, the support member being 10 resiliently extendable between a retracted position in which the flexible membrane does not prevent contact between the deactivating agent and the explosive composition and an extended position in which the flexible membrane prevents contact between the deactivation agent and the explosive composition. 15 One end of the support member is attached to an internal wall of the explosive cartridge and the other end of the support member is attached in the extended position to a release mechanism, wherein the release mechanism prevents movement of the support member between extended and retracted positions for a predetermined period of time. 20 In this particular embodiment the support member is attached in the extended position to a release mechanism. Due to the resilient nature of the support member this attachment results in the application of a force on the release mechanism and after a predetermined period of time this force results in activation of the release mechanism so that the end of the support member attached to the release mechanism is released thereby allowing the 25 support member to return to the retracted position. As the flexible membrane is attached to the support member, this will also mean that the flexible membrane will retract. In turn this allows deactivating agent previously separated from the explosive composition to be released and to contact the explosive composition. 30 The release mechanism is designed/adapted to allow the support member to move between extended and retracted positions after a predetermined period of time. Taking into account H:\kxg\Intenoven\NRPottbl\DCC\KXG\5412077_1.doc-23/09/2013 -7 the activity of the deactivation agent, this will be a period of time after which desensitisation of the explosive composition is desired following detonator failure of the explosive cartridge. This embodiment is therefore somewhat similar to the embodiments described above in which contact of the deactivating agent and explosive composition are 5 intentionally delayed. The flexible membrane may take the form of an elongate impermeable (rubber or plastic) sheath in which deactivating agent may be housed. The support member may conveniently take the form of an elongate helical spring to which the sheath is suitably attached along 10 the axis of the spring. The spring may be provided internally or externally relative to the sheath. The sheath is typically sealed at its lower end (the end attached to an internal wall of the cartridge) and open at the other end (the end closest to the release mechanism). The open end of the sheath will usually be sealed by a cap that includes one or more apertures through which deactivating agent may be released when the support member moves 15 between extended and retracted positions. When the support member is in the extended position the one or more apertures are sealed by corresponding structural features. The latter may take the form of a rubber O-ring or gasket that is displaced as the support member moves between extended and retracted positions thereby opening the one or more apertures to release deactivating agent. Once released the deactivation agent will come 20 into contact with the explosive composition. In its initial (unused) state the support member is in an extended position so that the flexible membrane prevents contact between the deactivation agent and the explosive composition. Sine the support member is resilient it exerts a withdrawing force against the 25 release mechanism to which it is attached. In one embodiment the release mechanism comprises a creep member to which one end of the support member is attached either directly or indirectly. The creep member is a length of material that has been selected based on its creep properties, that is the plastic 30 deformation properties of the material. In accordance with the invention the withdrawing force exerted by the support member is applied to the creep member thereby causing H:\xg\Iterwoven\NRPortbl\DCC\KXG\ 54 120 7 7 _ doc-23/09/2013 -8 plastic deformation of the creep member. When this plastic deformation reaches a particular (and predetermined) amount release mechanism causes the end of the support member to be suddenly released so that the support member reverts to the retracted position. As will be appreciated this causes the flexible membrane to collapse and the 5 deactivation agent to be released for contact with the explosive composition. The release mechanism is designed to achieve the release of the support member when the creep member has undergone a predetermined amount of creep. The end of the support member, or more likely the cap provided over the end of the flexible membrane (to prevent 10 escape of deactivation agent), may be attached directly to the creep membrane and in this case the ends of the creep member may be located at anchor points in the release mechanism or provided on internal walls of the explosive cartridge such that the predetermined amount of creep in the creep member will cause downward deflection of the creep member and release of the ends of the creep member from at least one of the anchor 15 points. In turn this allows the support member and associated flexible membrane to retract rapidly thereby releasing deactivating agent. In a preferred embodiment the support member is attached indirectly to the creep member. In this case the cap provided at the end of the support member may be adapted to be 20 releasably received by a corresponding fitting that is attached to or in contact with the creep member. It is intended that the cap will be released from the fitting only after the creep member has undergone a particular amount of creep (deflection). For example, the fitting may comprise (hinged) retaining arms that grip the cap and that have the ability to splay out when the cap/fitting assembly have been withdrawn a particular distance by the 25 support member as the creep member deforms under load from the support member. The retaining arms may be prevented from splaying outwardly and thus releasing the cap until this distance has been travelled by the configuration of internal walls provided in the release mechanism or cartridge. When the creep member has been deformed to a sufficient (predetermined) extent and the cap/fitting assembly has been withdrawn the corresponding 30 distance, the retaining arms are allowed to splay out thereby releasing the cap and enabling H:\kxg\Interwoven\NRPortbl\DCC\KXG\5412077_ldoc-23/09/2013 -9 the support member to return to the retracted position. This will cause release of the deactivating agent. In the extended position the support member will always exert a withdrawing force against 5 the creep member. However, to prevent the onset of creep in the creep member before use of the explosive cartridge, the cap or corresponding fitting may be held in place by a suitably designed locking mechanism that is released when the explosive cartridge is to be used. In one embodiment the locking mechanism takes the form of a sliding member that otherwise covers a detonator receiving passage provided in the explosive composition of 10 the cartridge. The act of moving the sliding member to reveal the detonator receiving passage, as would take place during use of the cartridge as a detonator is loaded into it, also has the effect of releasing the cap or fitting so that creep of the creep member is commenced under load of the support member. The sliding member may also be adapted to retain or guide detonator wires associated with the detonator after the sliding member 15 has been moved to allow placement of the detonator in the cartridge. In an embodiment of the invention the explosive cartridge of the invention includes another deactivating agent in addition to the deactivating agent that is separated from the explosive composition by the barrier element. The another deactivating agent may be of 20 the same or different type as the deactivating agent otherwise used in the explosive cartridge. This another deactivating agent may be provided separate to the explosive composition and must be mobilised in order for contact with the explosive composition to take place. In this case the another deactivating agent may be provided in dehydrated/dried form and is hydrated and made mobile by water that enters or is delivered into the 25 explosive cartridge when used. Water solubilises the another deactivating agent rendering it mobile. A water-permeable membrane may be used to separate the explosive composition and dehydrated deactivating agent with the deactivating agent permeating this membrane when mobilised by contact with water. It may also be possible to implement this embodiment using a water-degradable membrane to separate the explosive 30 composition and dehydrated deactivating agent. It is important that the membrane that is used is not degraded by the explosive composition.

H:\kxg\Intenvoven\NRPortbl\DCC\KXG\5412077_Ldoc-23/09/2013 -10 In this embodiment the explosive cartridge may include one or more inlets (apertures) or water-degradable pathways to allow environmental water to flow into the cartridge and into contact with the (dehydrated) deactivating agent. The membrane may define a cavity 5 or cavities that separate(s) the (dehydrated) deactivating agent and explosive composition with environmental water entering these cavities when the explosive cartridge is used. As a further variation of this embodiment water may be supplied into the explosive cartridge immediately prior to use. For example, an explosive cartridge could be suitably submerged in water prior to being positioned in a blasthole or the like, so that the water 10 enters the explosive cartridge as desired. Water may also be delivered into the explosive cartridge through a feed line. In an embodiment of the present invention the explosive composition may be deactivated by the combined activity of the deactivating agent (that is separated from the explosive 15 composition by the barrier element) as described herein and an additional deactivating agent that enters the explosive cartridge during use thereof. For example, the additional deactivating agent may be at least one microorganism that is present in the environment in which the explosive cartridge is being used and that is capable of acting on the explosive composition in order to convert it into by-products that are at least less detonable, and 20 preferably non-detonable, when compared with the explosive composition in its original form in the explosive cartridge. In an embodiment of the invention the additional deactivating agent acts on the explosive composition to render it more environmentally friendly (non-toxic), as might be useful in practice. 25 In this embodiment the at least one microorganism may be carried into the explosive cartridge in water present in the surroundings in which the cartridge is positioned (blastholes are typically wet environments). The cartridge may be designed to include apertures or inlets to allow ingress of environmental water, and thus microorganisms, into the body of the cartridge and into contact with the explosive composition. Channels may 30 be provided in and/or around the explosive composition to ensure a suitably high surface area of contact between incoming water/microorganisms and the explosive composition.

H:\kxg\ntemoven\NRPortbl\DCC\KXG\5412077_ I.doc-23/09/2013 - 11 In one embodiment the cartridge may include a water-permeable or water-degradable outer shell (membrane) surrounding the explosive composition, possibly with channels or passages extending into the explosive composition. In use water permeates or degrades the 5 shell (and channels/passages when present) thereby allowing the water and microorganisms to come into contact with the explosive composition. At that time the microorganisms begin to act on the explosive composition as intended. In another related embodiment the cartridge includes a shell and optionally 10 channels/passages formed of a material that will be dissolved by water and/or consumed by microorganisms present in the environment in which the cartridge is used. In this embodiment the microorganisms also have the ability to act on the explosive composition as described above. Desirably the microorganisms have a greater affinity for the material of the shell (and where present channels/passages) so that once the material is breached the 15 microorganism acts preferentially on the explosive composition. In these embodiments the time taken for the microorganism to come into contact with the explosive composition and the rate at which the microorganism acts on the explosive composition as desired (under prevailing conditions of use) is such that deactivation of the 20 cartridge will not be achieved until a predetermined amount of time has elapsed, prior to which the cartridge would normally have been detonated. In another embodiment the deactivating agent may be coated with a barrier element that is water-degradable or water-soluble. In this embodiment it is intended that on use of the 25 cartridge water will enter the cartridge, via one or more mechanisms described herein, and dissolve or degrade the barrier element thereby rendering active the deactivating agent. In this case the deactivating agent may take the form of particles coated with a suitable barrier element. By way of example, the deactivating agent may be iron powder. 30 In a slight variation of this the deactivating agent may require another agent in order to be active with this other agent being released for contact with the deactivation agent in H:\kxg\Interwoven\NRPortbi\DCC\KXG\5412077_1.doc-23/09/2013 - 12 accordance with the embodiments of the invention. For example, iron in dry form has some degrading effect on PETN and TNT but this effect is dramatically increased when the iron is in an aqueous (wet) environment. In this case removal of the barrier element results in contact of a reagent with the deactivating agent, and wherein the reagent renders 5 the deactivating active or potentiates the activating of the deactivating agent with respect to the explosive composition. In both of these latter embodiments the deactivating agent may be distributed throughout the explosive composition. 10 The explosive composition used in the explosive cartridge of the invention is conventional in nature and will be selected based on its ability to be desensitised by the deactivation agent or agents to be used. Examples of explosive materials that may be considered for use in the present invention include trinitrotoluene (TNT), pentaerythritol tetranitrate 15 (PETN), cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX). The explosive composition may be an emulsion explosive, a water-gel explosive composition or an ANFO or other nitrate-based composition. Other less conventional explosives may also be used such as liquid or gel compositions which are aqueous or non aqueous and possibly containing other explosive components such as perchlorates. 20 Combinations of explosive materials may also be used. For example, the explosive composition may be Pentolite, a mixture of PETN and TNT. In one embodiment of the present invention the explosive composition may be a water-in oil emulsion. Emulsion explosive compositions typically includes a discontinuous phase 25 comprising a supersaturated aqueous solution of an oxidiser salt (usually ammonium nitrate) dispersed in a continuous oil (fuel) phase. Such emulsions are usually formed by mixing the components in the presence of a suitable emulsifier. In the context of emulsion explosive compositions, the deactivating agent may include any reagent that is capable of breaking or rendering unstable the emulsion, thereby causing it to be insensitive to 30 detonation. Usually, the deactivating agent will have the effect of causing crystallisation of the supersaturated emulsion component (the oxidiser salt in the type of emulsions H:\kxg\Intenoven\NRPortbl\DCC\KXG\5412077_I.doc-23/09/2013 - 13 described). Accordingly, one skilled in the art may select suitable reagents for use as deactivating agent, at least for initial screening, based on a general knowledge of emulsion chemistry and of reagents that are known to cause unwanted crystallisation of (supersaturated) emulsion explosive compositions. Here it is important to note that the 5 present invention seeks to make positive use of reagents that might previously have been regarded as being detrimental in the context of emulsion explosive compositions. The type of deactivating agent used will usually be selected on the basis of the emulsion explosive composition being used rather than vice versa. 10 The present invention has particular utility in seismic survey applications and in this case the explosive cartridge takes the form of a seismic charge. One skilled in the art will be familiar with the type of explosives in this context. In an embodiment of the present invention the deactivating agent is a chemical. In this 15 context the term "chemical" refers to a non-biological reagent that is capable of desensitising the explosive composition in order to render it insensitive to detonation. The exact mechanism by which this is achieved is not believed to be critical. The deactivating agent may cause structural changes in the explosive composition leading to a reduction or loss of detonation sensitivity. The deactivating agent may vary as between different types 20 of explosive composition and as between different formulations of the same type of explosive composition. The effectiveness of a deactivating agent with respect to any given explosive composition may be determined experimentally. It will be appreciated from this definition that the chemical does not embrace biological 25 based deactivating agents as will be described below. It will also be appreciated that the effect of the chemical with respect to the explosive composition is more than as a simple solvent, although it is possible that the chemical poison may have the effect of dissolving one or more components of the explosive composition. It will be noted that in US 3,948,177 deactivation of the explosive charge results due to dissolution of the explosive 30 charge and, possibly due to the explosive charge being carried out of the explosive cartridge as a result of dissolution. It is to be appreciated that the use of water (alone) as H:\kxg\Intenvoven\NRPortbl\DCC\KXG\5412077_1.doc-23/09/2013 - 14 chemical poison is not within the context of the present invention. Under the conditions of intended use the chemical is usually a liquid. Chemicals useful in the present invention for remediating explosives are known in the art. 5 For example, it is known that TNT, RDX and HMX may be remediated in contaminated soil by alkaline hydrolysis using suitable chemical reagents. It is also known to remediate RDX-contaminated soil using zero-valent iron. It is also known to degrade nitro containing explosives such as TNT, RDX, HMX and PETN by contact with a solution comprising a superoxide salt, such as potassium superoxide and sodium superoxide. 10 Useful chemicals for any given explosives material may be determined experimentally. The examples included in the present specification describe this and identify chemical poisons that may be used to desensitise water-in-oil emulsion explosive compositions. In an embodiment of the present invention the deactivating agent relies on the use of one 15 or more types of microorganism to desensitise the explosive composition by degrading the explosive composition into less explosive materials or non-explosive materials. The microorganisms may further comprise a type of microorganism that further bioremediates any intermediate chemicals resulting from the bioremediation action of the first type of microorganisms to fully bioremediate the explosive material into non-explosive materials. 20 Any type of microorganism capable of desensitising explosive material is considered to be useful within the context of the present invention. Examples of microorganisms that are known to exhibit that ability include Pseudomonas spp., Escherichia coli, Morganella morganii, Rhodococcus spp., Comamanos spp., and denitrifying bacteria. Suitable 25 Pseudomonas spp. microorganisms include microorganisms in the group aeruginosa, fluorescens, acidovorans, mendocina, cepacia. The present invention may utilise any of numerous different selections of microorganisms capable of degrading explosive materials in any of various relative quantities. Each of 30 these various selections of microorganisms will hereinafter be referred to as a "microorganism consortium". In such a microorganism consortium, one type of H:\xg\ itenv n\NRPorbl\DCC\KXG\541207 7-.doc-23/09/2013 - 15 microorganism can advantageously reduce the explosive material to a particular intermediate chemical, while that type or another type of microorganism may further the reduce the benzene to carbon chains or to individual carbon atoms. In one embodiment, a microorganism consortium may be utilised based on various of the microorganisms 5 belonging to Pseudomonas spp., Escherichia coli, Morganella morganii, Rhodococcus spp., comamonas spp., and denitrifying bacteria. The microorganism(s) used in accordance with this embodiment must be viable under the conditions of intended use. If aerobic microorganisms are being used it will obviously be 10 necessary for oxygen to be available to the microorganism(s). It may also be necessary to provide nutrients for the microorganism in order for the microorganism to function as intended to desensitise explosive material. One skilled in the art would be aware of such things. 15 The microorganism may be provided in the explosive cartridge in a ready to use form so that upon contact with the explosive composition the microorganism commences desensitisation of the explosive composition by degradation of it. In an embodiment of the invention the microorganism(s) are provided in dehydrated form and must be hydrated before they exhibit the request activity. Hydration may take place using water when the 20 barrier element in the explosive cartridge is at least partially removed, as described. As well as deactivating the explosive composition, desirably the deactivating agent also converts the explosive composition (or components thereof) into one or more compounds that are more environmentally acceptable. 25 A combination of the same or different type of deactivating agents may be used in practice of the present invention. The present invention also relates to a blasting system that comprises an explosive 30 cartridge in accordance with the present invention, and to the use of such explosive H:\kxg\lntenvoven\NRPoitbl\DCC\KXG\5412077_ .doc-23/09/2013 - 16 cartridge in a blasting operation. As has been explained, the present invention is likely to find particular utility in the context of seismic exploration. Embodiments of the present invention are illustrated in the accompanying non-limiting 5 figures, in which: Figures 1-3 are graphs illustrating experimental results obtained in certain examples described herein; 10 Figures 4-7, are photographs illustrating experimental results obtained in certain examples described herein; Figures 8-12 are cross-sections of an explosive cartridge in accordance with the present invention. These figures represent various cross-sectional views of the same explosive 15 cartridge; Figure 8 shows an explosive cartridge (1) suitable for use in seismic exploration. The explosive composition and deactivating agent remain sealed in their respective chambers (2, 3). The deactivation agent is confined by a flexible membrane that is in the form of an 20 elongate plastic or rubber sheath (11). The sheath (11) is closed at one end at the base of the cartridge (1) and sealed at the other end by a cap (12). A support member in the form of a helical spring (13) is provided internal to the sheath (11). The helical spring (13) is anchored at its lower end to an internal wall of the 25 cartridge (1). At its upper end the helical spring (13) is attached to the cap (12) that seals the sheath (11). The helical spring (13) supports the sheath (11) and in the embodiment shown the flexible membrane is in an extended position. In this position the deactivating agent is prevented from contacting the explosive composition. The cap (12) engages a release mechanism and this is more clearly illustrated in Figures 9-11. 30 H:\kxg\Intenvoven\NRPortbl\DCC\KXG\5412077_l.doc-23/09/2013 - 17 Figures 9-12 show the cap (12) being gripped by a pair of retaining arms (14). These arms (14) are hinged towards their upper ends and themselves extend from a fitting (15). The cap (12) is configured to be gripped by the arms (14) and in the embodiment shown the cap (12) has shoulder portions under which the arms (14) are initially positioned. Towards its 5 upper end the fitting (15) is in contact with a creep member (16) in the form of a plastic rod having known creep properties. In the extended position the helical spring (13) will exert a withdrawing force against the creep member (16) through the cap/fitting (12, 15) assembly. Prior to use of the cartridge (1) this force is prevented from deforming the creep member (16) by a sliding member (17) that engages the upper end of the fitting such that 10 downward movement of the fitting (15) and thus of the creep member (16) are prevented. In the extended position the arms (14) are prevented from splaying outwards about their hinges due to the configuration of adjacent internal wall portions of the cartridge (1). Prior to use the sliding member (16) engages the fitting (15) and covers a detonator 15 receiving passage (18) provided in the cartridge (1). When the cartridge (1) is used in the field the sliding member (17) is moved across to reveal the detonator receiving passage (18) allowing a detonator (5) to be inserted into the body of the cartridge (1). The detonator wires (5A) are guided and retained by wall portions (1 7A) provided on the sliding member (17). It will be appreciated that in the embodiment shown the detonator 20 (5) cannot be inserted into the detonator receiving passage (18) until the sliding member (17) has been moved across from the position in which it engages the upper end of the fitting (15). When the fitting (15) is no longer engaged by the sliding member (17) the withdrawing 25 force exerted by the helical spring (13) will be communicated to the creep member (16). In turn this will initiate creep (and downward deflection) in the creep member (16). Figure 10 shows the initial situation on release of the fitting (15) from engagement with the sliding member (17). The fitting (15) has been withdrawn slightly into the body of the cartridge (1) but further downward movement of it is prevented by suitably positioned 30 retaining legs (19) provided on an internal wall of the cartridge (1). At this point the withdrawing force exerted by the helical spring (13) is experienced by the creep member H:\kxg\Intenvovn\NRPortb\DCC\KXG\5412077_I.doc-23/09/2013 - 18 (16). The creep member (16) will be deformed under load of the helical spring (13) causing deflection of the creep member (16). This is shown more clearly in Figure 11. Downward deflection of the creep member (16) will allow the cap/fitting (12,15) assembly 5 to move downwards into the body of the cartridge (1). When the cap/fitting (12,15) assembly has travelled a predetermined distance the retaining arms (14) are allowed to splay out by virtue of shape of the relevant internal wall portions of the cartridge (1). The shoulders of the cap (12) have the effect of forcing the arms (14) outwardly but this movement is initially constrained by suitably shaped internal wall portions of the cartridge 10 (1). When the arms (14) are splayed out the fitting (15) no longer engages the cap (12) and the cap (12) is suddenly released. Residual tension in the helical spring (13) continues to act on the cap (12) however so it is withdrawn further into the body of the cartridge (1). As the helical spring (13) travels from its extended position to retracted position the sheath 15 (11) will collapse forcing deactivating agent out through holes provided in the cap (12). The deactivation agent is then free to contact the explosive composition so that desensitisation is commenced. Embodiments of the present invention are now illustrated in the following non-limiting 20 examples. Example 1 This example was undertaken to assess the effect as deactivating agent of a number of 25 different reagents. The reagents selected for initial screening were chosen based on a general knowledge of emulsion chemistry and of reagents that had caused unwanted crystallisation of emulsion explosive compositions. All reagents were used as liquids and can be categorised as water soluble, oil soluble or polar organic. Water was used as a control liquid. The following table details the various liquids used in this experiment. 30 H:\kxg\Interwoven\NRPortbl\DCC\KXG\5412077_1.doc-23/09/2013 - 19 Table 1 Class Material Details Water soluble Water (test control) Ferric chloride 42% solution Ferrous sulphate 10% solution Magnesium nitrate 10% solution Teric GN8 detergent 10% solution Petro AG Special Liquid 50% solution in water Oil soluble Propar 32 paraffin oil (test control) Galoryl 626 10% solution in Propar 32 Galoryl 640 10% solution in Propar 32 Polar organic liquids Ethane-1,2-diol Pure liquid Polyethylene glycol 600 Pure liquid Propan- 1,2-diol Pure liquid Propan-2-ol Pure liquid iso-Amyl alcohol Pure liquid n-Hexylamine Pure liquid Cyclo-Hexylamine Pure liquid Octylamine Pure liquid Acetone Pure liquid Teric GN8 is a 10% solution of nonylphenol ethoxylate oligomer with 8 ethoxylate units, 5 commercially available from Orica. Petro AG Special Liquid is a 50% solution of sodium alkylnaphthalene sulphonate, commercially available from Akzo Nobel. 10 The screening test involved providing a 20ml layer of the reagent under test on top of 30g of a typical emulsion explosive composition provided in a 100ml glass beaker. The composition of the emulsion explosive composition is given in Table 2 below.

H:\kxg\Initeroven\NRPortbl\DCC\KXG\5412077 1.doc-23/09/2013 - 20 Table 2 Component wt.% Ammonium nitrate 67.99 Sodium nitrate 3.01 Sodium perchlorate 10.45 pH buffer 0.34 Water 12.31 Emulsifier* 2.76 Sorbitan mono-oleate 0.56 Paraffin oil 2.58 100.00 *Adduct of polyisobutylene succinic anhydride with diethanolamine, diluted to approximately 50% solution in paraffin oil. 5 Batches of the emulsion were prepared by as follows. Ingredients sufficient for a total emulsion mass of 3.0 kg were weighed out. Ammonium nitrate, sodium nitrate, sodium perchlorate (anhydrous), 30% lactic acid solution (neutralised to pH = 4 with sodium carbonate) and water were heated and stirred in a water-jacketed tank to form a solution 10 with a temperature of 90'C. In the bowl of a 3 speed Hobart model N-50 planetary mixer (water-jacketed and heated to 90'C), the components, paraffin oil, sorbitan mono-oleate and PiBSA-DEA were stirred with a wire whisk attachment at Speed setting 2 to form an oil/emulsifier solution at 90'C. With the Hobart mixer stirring at Speed 2, the nitrate/perchlorate solution was added evenly to the oil/emulsifier solution over the course 15 of 5 minutes, forming an emulsion of the water-in-oil type. The mixer speed was increased to Speed 3 for a further 5 minutes, giving a final emulsion product with viscosity 70,000 centipoise at 70'C (as measured using a Brookfield RVT viscometer with spindle 1 at 50 rpm). 20 After the layer of reagent was provided on top of the emulsion explosive composition the condition of the emulsion was monitored. Reagents were rated according to how fast they penetrated and damaged the emulsion. This was assessed based on visual colour and texture changes of the emulsion and this was taken as being representative of the degree of crystallisation. The results for the water soluble, oil soluble and polar organic, liquids are 25 illustrated in Figures 1, 2 and 3, respectively.

H:\kxg\Intenvoven\NRPo nbl\DCC\KXG\54120?77 1.doc-23/09/2013 -21 The chemistry of Petro AG Special Liquid is obviously important but reference to this, or any other, commercial product should not be regarded as limiting the present invention. Reference to commercial products in the present specification is intended to show that the 5 invention may be implemented on the basis of existing products. Materials for use in practice of the invention may of course be prepared, rather than purchased, by the application or adaptation of known techniques. Example 2 10 While some of the polar organic liquids tested provided relatively rapid and effective penetration of the emulsion explosive composition, Petro AG Special Liquid was selected as the reagent with the best overall performance. Petro AG Special Liquid is a 50% strength solution of sodium alkyl naphthalene sulphonate in water and is commercially 15 available from Akzo Nobel. This reagent is also useful in practice of the present invention from a number of other perspectives (it is water based non-flammable, has relatively low toxicity and odour, is non-volatile, may be manufactured in a non-hazardous and easy manner and is commercially available). 20 As further indication of the efficacy of the using Petro AG Special Liquid, Figure 4 and 5 are photographs showing the effect of Petro AG Special Liquid on an emulsion explosive composition of the type identified in Table 2. In Figure 4 the layer of Petro AG Special Liquid has just been provided on top of the emulsion explosive composition. The layer of Petro AG Special Liquid appears as a darker layer provided over the top of the lighter 25 emulsion explosive composition provided in the bottom of the beaker. From the scale included in the photograph it can be seen that the emulsion explosive composition initially was approximately 3cm in depth and the Petro AG Special Liquid approximately 1.5cm. Figure 5 shows the same beaker after the Petro AG Special Liquid has been in contact with the emulsion explosive composition for a period of two days. The effect of the Petro AG 30 Special Liquid is believed to be immediately apparent when one compares Figures 4 and 5 side-by-side. It will be noted that the "level" of emulsion composition has dropped by H:\kxg\nterwoven\NRPortbl\DCC\KXG\5412077 l.doc-23/09/2013 - 22 approximately lcm (effectively 33%). This shows that the Petro AG Special Liquid has had a significant impact on the integrity of the emulsion explosive composition. For comparison, the experiment was repeated using a commercially available detergent 5 (Teric GN8). The results are shown in Figure 6 at the commencement of the test and Figure 7 after five days. The Teric GN8 and the emulsion explosive composition are not of sufficiently different colours for the interface between the two to be seen clearly in Figures 6 and 7. However, a marker has been included on the outside surface of the beaker to show the position of the interface between the two. It is immediately apparent that, even 10 after five days, the detergent has had little effect on the emulsion explosive composition. It is possible that the detergent causes some crystallisation at the interface with the emulsion explosive composition but it is evident that Petro AG Special Liquid causes massive crystallisation several centimetres away from the interface and within the body of the emulsion explosive composition. The exact mechanism by which this crystallisation 15 occurs is not well understood but this is not material to the invention. Example 3 When actively mixed into an emulsion explosive composition (as per Table 2), as opposed 20 to simple surface contact, about 3% by weight of Petro AG Special Liquid was required to cause enough crystallisation to render a 63mm diameter charge insensitive to a No. 8 detonator. The relationship between the amount of reagent (deactivating agent) used, the degree of crystallisation and the detonation performance is that 3% is the theoretical minimum amount of Petro AG Special Liquid that would need to be available in a 25 self-deactivating cartridge in accordance with the present invention. Example 4 In the proposed explosive cartridge in accordance with the present invention there is no 30 active mixing of the deactivating agent and emulsion explosive composition. Indeed, there is only a static surface exposure of these two components. To examine whether this is H:\kxg\Interoven\NRPortbl\DCC\KXG\5412077_I.doc-23/09/2013 -23 sufficient to deactivate an emulsion explosive composition, paper-walled axial cavities (10mm and 12 mm in diameter, respectively) were created inside 57mm diameter emulsion charges. Each cavity was filled with Petro AG Special Liquid. Being porous, the paper allowed the Petro AG Special Liquid to instantly contact the emulsion explosive 5 composition. This may be regarded as simulating the end of the period at which time a wall of material degradable by the deactivating agent loses its integrity and exposes the emulsion explosive composition to the deactivating agent. In this example the amount of Petro AG Special Liquid in a 10mm cavity equates to 3% w/w of the charge while the 12mm cavity equates to 5% w/w of the charge. 10 For both cavity sizes it was observed that crystallisation of the emulsion proceeded slowly radially outward from the axis of the cavity. The charges became highly crystallised and were found to be detonator-insensitive within one month, as confirmed by velocity-of detonation (VOD) tests. 15 Example 5 500 ml water was heated to 45'C in a water bath. Pentolite was added to 200ppm (200mg/L), consisting of 70ppm PETN and 130ppm TNT. Sodium hydroxide solution 20 (0.004 M) was added in an amount of 0.2ml from a stock solution of 10M. The resultant solution was then removed from the water bath and allowed to sit at room temperature (21 C) overnight in the dark. Samples were taken and analysed for PETN and TNT levels. The experiment was repeated using water as control. The results are presented in Table 3 below. 25 Table 3 PETN TNT (mg/L) (mg/L) NaOH (0.004M) 40 1.0 Water 45 110 H:\kxg\nenmoven\NRPobl\DCC\KXG\5412077_1.doc-23/09/2013 - 24 Table 3 demonstrates the conversion of TNT by the action of the strong alkali sodium hydroxide. Surprisingly, little or no detectable activity is present on the PETN molecule. 5 Conversion of TNT by alkali is well established in the art and is known to proceed via mechanisms including, but not limited to, chemical reduction of the nitrate groups and/or removal of the nitrate groups. The action of alkali on TNT is well established in the art for destruction of TNT. It has, 10 however, to the authors knowledge, never been incorporated into an explosive device for purposes including, but not limited to, rendering the device less prone to initiation and more amenable to biodegradation. This demonstration of the conversion of TNT in a Pentolite solution confirms that an alkali 15 can be used to enhance the degradation of explosive devices, including Pentolite based devices. Example 6 20 Iron degradation control In this example, coated iron particles are used to demonstrate the effect of NaCl addition in enhancing the degradation of Pentolite, presumably by effecting either, degradation of the barrier or, 'de-passivation' of the iron particles. This example has broad application as iron 25 particles may be maintained in a non-functional state until NaCl is released, thus initiating degradation of the Pentolite. Experimental 30 Iron powder (Cat.no. 00631, Fluka, Australia)(150 mg) was added to 3ml RNW buffer (1 mM KHCO3, 0.5 mM CaCl2, 0.206 mM MgSO4, 8.95 ptM FeSO4, 0.25 mM HCl, pH H:\kxg\Intenvoven\NRPonbt\DCC\KXG\5412077_l.doc-23/09/2013 -25 -7.8). To one set of iron containing tubes NaCl was added at 3mM whilst a non-iron containing control was established with only RNW and 3mM NaCl. The reaction commenced with the addition of Pentolite (acetone) solution to a final concentration of 100ppm. Sacrificial sampling was performed for analysis after 1, 15 or 51 days' incubation 5 at room temperature in the dark. Samples were processed for analysis by addition of 9 mL of acetonitrile and subsequently analysed by HPLC-UV using standard methods. Results of analysis are shown in the following table, demonstrating control of iron degradation of Pentolite by the use of a corrosion enhancer. Degradation of Pentolite 10 increases in a time-dependent manner and is initiated by the presence of a corrosion enhancer. NaCl mediated degradation of Pentolite by Iron powder PETN %TNT / Sample Time (days) PETN (mg/L)TNT (mg/L) degradation degradation 1 31.2 64 0% 0% Control RNW 15 33.2 68 0% 0% 51 35.2 59.6 0% 0% 1 31.2 64 0% 0% Iron 15 52 68 0% 0% 51 36 60 0% 0% 1 31.2 64 0% 0% Iron + NaCl 15 32 21.2 3.6% 68.8% 51 15.2 <0.4 56.8% >97% H:\kxg\Intenvoven\NRPortbl\DCC\KXG\5412077_ I.doc-23/09/2013 - 26 Example 7 Iron degradation control 5 A control mechanism to maintain iron in an 'inactive' state for a predetermined period (shelf-life) is of key relevance to it's successful application. This control mechanism can be provided by coating the iron in a degradable barrier, preferably a water soluble barrier. Experimental 10 Iron powder (Cat.no. 12311 - Reidel-deHaen, Australia) (30 mg) was added to two sets of tubes and Pentolite stock solution was added directly to the iron powder and the acetone allowed to evaporate (dry). Alternatively, iron was added to RNW buffer (1 mM KHCO 3 , 0.5 mM CaCl 2 , 0.206 mM MgSO 4 , 8.95 tM FeSO 4 , 0.25 mM HCl, pH -7.8) to make a 15 100 ppm Pentolite solution and thus suspending the iron powder (wet). Control tubes contained Pentolite stock solution only. Tubes were sacrificed for analysis after 3 days and 10 days incubation at room temperature in the dark. Samples were processed for analysis by addition of 9 mL of acetonitrile and subsequently analysed by HPLC-UV using standard methods. 20 Results are shown in the following table, demonstrating control of iron degradation of Pentolite. Degradation of Pentolite was accompanied by corrosion of the iron powder with an orange oxide layer forming above the grey iron powder.

H:\kxg\Intenvovn\N RPortb1\DCC\KXG\5412077_l-doc-23/09/2013 - 27 Degradation of Pentolite by iron wet form, but not dry form Sample Time PETN TNT PETN TNT (days) (mg/L) (mg/L) degradation degradation Control 3 35.2 72.4 0% 0% 10 33.6 60.8 0% 0% Dry iron 3 7.6 77.2 0% 0% 10 34.8 65.2 0% 0% Wet iron 2.8 0.4 92% 99% 10 1.2 <0.4 96% 99% Example 8 5 Degradation of PETN (SPC) Sodium percarbonate (SPC) has been used in the present example as it is a stable solid complex of Sodium Carbonate and Hydrogen Peroxide. This compound thus combines 10 oxidative power, which, once exhausted, leaves an alkaline environment to degrade alkali sensitive compounds eg. TNT. In addition to these 'simple' reactions, peroxide can establish catalytic cascades, particularly, but not exclusively, in the presence of metals (eg. Iron). 15 Experimental Sodium Percabonate (SPC) was purchased from Sigma-Aldrich, Australia (Cat# 371432) and solutions, once prepared, were used immediately. A 100 mM SPC solution was made in RNW buffer, which is a water-based buffer exhibiting moderate general hardness and 20 alkalinity (1 mM KHCO 3 , 0.5 mM CaC1 2 , 0.206 mM MgSO 4 , 8.95 pM FeSO 4 , 0.25 mM HCl, pH -7.8). Two ten-fold serial dilutions were made of this solution into the same buffer, representing 10mM and 1mM SPC. A Pentolite (acetone) solution was added to 2 00ppm in a volume of 3mL per reaction and incubated at room temperature overnight in H:\kxg\lntevoven\NRPontbl\DCC\KXG\5412077_I.doc-23/09/2013 -28 the dark. Samples were sacrificed by addition of 9 mL acetonitrile and TNT/PETN were analysed by HPLC-UV using standard methods. Degradation of Pentolite by sodium percarbonate PETN %TNT % Sample PETN (mg/L) TNT (mg/L) degradation degradation Control 59.2 119.6 0% 0% 1 mM SPC 57.6 102.8 2.7% 14% 10 mM SPC 53.6 2.8 9.5% 97.7% 100 mM SPC 10 <0.4 83.1% 99.7% 5 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia. 10 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (8)

1. An explosive cartridge comprising: an explosive composition; a deactivating agent that is capable of desensitising the explosive composition; and a barrier element that prevents contact between the explosive composition and the deactivating agent and that is adapted to be at least partially removed on use of the explosive cartridge, wherein the barrier element takes the form of flexible membrane attached to a support member, the support member being resiliently extendable between a retracted position in which the flexible membrane does not prevent contact between the deactivating agent and the explosive composition and an extended position in which the flexible membrane prevents contact between the deactivating agent and the explosive composition, one end of the support member being attached to an internal wall of the explosive cartridge and the other end of the support member being attached in the extended position to a release mechanism, wherein the release mechanism prevents movement of the support member between extended and retracted positions for a predetermined period of time.

2. An explosive cartridge according to claim 1, wherein the flexible membrane takes the form of an elongate impermeable sheath in which deactivating agent is housed.

3. An explosive cartridge according to claim 2, wherein the support member takes the form of an elongate helical spring to which the sheath is suitably attached along the axis of the spring.

4. An explosive cartridge according to claim 1, wherein the release mechanism comprises a creep member to which one end of the support member is attached either directly or indirectly, the creep member comprising a length of material that has been selected based on its creep properties so that a withdrawing force exerted by the support member is applied to the creep member thereby causing plastic deformation of the creep H:\kxg\Interoven\NRPortbl\DCC\KXG\5412077 _.doc-23/09/2013 - 30 member, and the support member is released when the creep member has undergone a predetermined amount of creep.

5. An explosive cartridge according to claim 4, wherein the support member is attached indirectly to the creep members via a cap provided at the end of the support member that is adapted to be releasably received by a corresponding fitting that is attached to or in contact with the creep member, the cap being released from the fitting only after the creep member has undergone a particular amount of creep.

6. Use of an explosive cartridge according to claim 1 in a seismic survey application, wherein the explosive cartridge takes the form of a seismic charge.

7. An explosive cartridge according to claim 1, substantially as hereinbefore described.

8. Use according to claim 6, substantially as hereinbefore described.