Deactivating an explosive composition using a chemical

Abstract

A method of deactivating an explosive composition provided in an explosive cartridge, which method comprises exposing the explosive composition to a deactivating agent that renders the explosive composition insensitive to detonation, wherein the deactivating agent is a chemical.

Claims

1. A method of deactivating an explosive cartridge in a blasting operation during mining, quarrying, or seismic exploration in which an explosive composition provided in an explosive cartridge is rendered insensitive to detonation after a predetermined amount of time, comprising the following steps: (a) positioning the explosive cartridge in a borehole and priming the explosive cartridge with an initiating device; (b) contacting the explosive composition with a chemical deactivating agent that is contained in the explosive cartridge and that is capable of reacting with the explosive composition to render the explosive composition insensitive to detonation; and (c) allowing the chemical deactivating agent to react with the explosive composition so that the explosive composition is rendered insensitive to detonation by the initiation device, wherein the explosive composition remains sensitive to detonation by the initiating device for a controlled amount of time after the explosive cartridge has been positioned in the borehole and primed with the initiation device, the controlled amount of time being less than the predetermined amount of time, and wherein steps (b) and (c) take place so that the explosive composition is rendered insensitive to detonation following the predetermined amount of time, and wherein the chemical deactivating agent and explosive composition are separated by a barrier element and wherein the barrier element is ruptured or removed by (i) insertion of the initiating device into the cartridge, thereby causing the chemical deactivating agent and explosive composition to come into contact with each other, or (ii) connecting one of the explosive cartridges to another of the explosive cartridges.

2. A method according to claim 1, wherein the explosive composition is TNT, RDX or HMX, and the chemical deactivating agent causes alkaline hydrolysis of the explosive composition.

3. A method according to claim 1, wherein the explosive composition comprises RDX and the chemical deactivating agent comprises zero-valent iron.

4. A method according to claim 1, wherein the explosive composition is a nitro-containing explosive and the chemical deactivating agent is a solution comprising a superoxide salt.

5. A method according to claim 1, wherein the explosive composition is desensitised through the combined activity of the chemical deactivating agent and another reagent useful in deactivating the explosive composition.

6. A method according to claim 5, wherein the another reagent is a reagent external to the explosive cartridge that enters the cartridge, or is introduced into the cartridge during use thereof and that can contribute to desensitisation of the explosive composition.

7. A method according to claim 6, wherein the explosive cartridge is adapted to allow the another reagent to be introduced into or enter the explosive cartridge as required.

8. The method according to claim 1, wherein the explosive cartridge is a seismic charge.

9. The method according to claim 1, wherein the barrier element is ruptured or removed by insertion of the initiating device into the cartridge, thereby causing the chemical deactivating agent and explosive composition to come into contact with each other.

10. The method according to claim 1, wherein the barrier element is ruptured or removed by connecting one of the explosive cartridges to another of the explosive cartridges.

11. A method of deactivating an explosive cartridge in a blasting operation during mining, quarrying, or seismic exploration in which an emulsion explosive composition provided in an explosive cartridge is rendered insensitive to detonation after a predetermined amount of time, comprising the following steps: (a) positioning the explosive cartridge in a borehole and priming the explosive cartridge with an initiating device; (b) contacting the emulsion explosive composition with a chemical deactivating agent that is contained in the explosive cartridge and that is capable of rendering the emulsion explosive composition unstable thereby causing the emulsion explosive composition to be insensitive to detonation; and (c) allowing the chemical deactivating agent to act on the emulsion explosive composition so that the emulsion explosive composition is rendered insensitive to detonation by the initiation device, wherein the emulsion explosive composition remains sensitive to detonation by the initiating device for a controlled amount of time after the explosive cartridge has been positioned in the borehole and primed with the initiation device, the controlled amount of time being less than the predetermined amount of time, and wherein steps (b) and (c) take place so that the emulsion explosive composition is rendered insensitive to detonation following the predetermined amount of time and wherein the chemical deactivating agent and emulsion explosive composition are separated by a barrier element and wherein the barrier element is ruptured or removed by (i) insertion of the initiating device into the cartridge, thereby causing the chemical deactivating agent and emulsion explosive composition to come into contact with each other, or (ii) connecting one of the explosive cartridges to another of the explosive cartridges.

12. A method according to claim 11, wherein the emulsion explosive composition is desensitised through the combined activity of the chemical deactivating agent and another reagent useful in deactivating the emulsion explosive composition.

13. A method according to claim 12, wherein the another reagent is a reagent external to the explosive cartridge that enters the cartridge, or is introduced into the cartridge during use thereof and that can contribute to desensitisation of the emulsion explosive composition.

14. A method according to claim 13, wherein the explosive cartridge is adapted to allow the another reagent to be introduced into or enter the explosive cartridge as required.

15. The method according to claim 11, wherein the explosive cartridge is a seismic charge.

16. The method according to claim 11, wherein the barrier element is ruptured or removed by insertion of the initiating device into the cartridge, thereby causing the chemical deactivating agent and emulsion explosive composition to come into contact with each other.

17. The method according to claim 11, wherein the barrier element is ruptured or removed by connecting one of the explosive cartridges to another of the explosive cartridges.

Description

(1) Embodiments of the present invention are illustrated in the accompanying non-limiting figures, in which:

(2) FIGS. 1-3 shows a cross-section of explosive cartridges in accordance with the present invention, with FIGS. 2 and 3 illustrating the same design;

(3) FIGS. 4-6 are graphs illustrating experimental results obtained in certain examples described herein;

(4) FIGS. 7-10, are photographs illustrating experimental results obtained in certain examples described herein; and

(5) FIGS. 11 and 12 are perspective views of explosive cartridges in accordance with the present invention.

(6) FIG. 13 is a cross-section of an explosives cartridge in accordance with the present invention; and

(7) FIGS. 14 and 15 are perspective views showing a component of the explosives cartridge depicted in FIG. 13.

(8) Thus, FIG. 1 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). Therefore, subject to the stability of the emulsion explosive composition, the cartridge (1) is a storage stable product.

(9) The cartridge also includes a small diameter axial channel (4) extending down within the body of the cartridge (1) from the deactivating agent chamber (3) through the explosive composition. This channel (4) is defined by a wall formed from a polymeric material that is degradable on contact with the deactivating agent. In the arrangement shown in FIG. 1 the channel (4) is empty since the deactivating agent has not been released from the chamber (3). A seal (not shown in detail) is provided between the deactivating agent chamber (3) and the channel (4), this seal being designed so that breakage of it will cause release of deactivating agent from chamber (3) into channel (4) extending through the explosive composition.

(10) The upper end of the cartridge (1) is adapted to receive a cylindrical detonator (5). When the cartridge (1) is to be used in the field, this detonator (5) is inserted into a detonator-receiving channel (6) extending into the body of the cartridge (1). In the embodiment shown the detonator-receiving channel (6) is provided as an extension of the channel (4). The action of inserting the detonator into the detonator-receiving channel (6) causes the seal between the deactivating agent chamber (3) and the channel (4) to be broken thereby releasing deactivating agent into the channel (4). However, contact between the deactivating agent and the explosive composition is prevented by the walls of the channel (4) and the deactivating agent must first penetrate these walls before contacting explosive composition.

(11) Although not shown, it may be necessary for the design to include some kind of air inlet (or breather tube) to allow air into the deactivating agent chamber (3) as deactivating agent flows out. In the absence of an air inlet, flow of deactivating agent may be restricted. Generally, air will only be allowed into the deactivating agent chamber (3) when the cartridge is being used, thereby preventing leakage of the deactivating agent.

(12) Surface tension effects of the deactivating agent may also influence design or the characteristics of the deactivating agent to be used. Although also not shown it may be useful to allow the deactivating agent once released to come into contact with a wick or open cell foam that extends down into the channel (4) and that has the effect of conducting/drawing deactivating agent down into the channel (4).

(13) The walls of the channel (4) are made of a degradable (polymeric) material that may be hydrolysed by water present in the aqueous deactivating agent. On contact of the deactivating agent and the walls of the channel (4) the deactivating agent therefore (slowly) degrades the walls. Whilst the walls remain intact no contact of the deactivating agent and explosive composition takes place and this delay allows a user of the cartridge (1) sufficient time to load the cartridge into a blasthole and attempt detonation of the cartridge (1) as intended. Thus, the functionality of the cartridge (1) remains intact even though the deactivating agent has been released from the chamber (3) originally containing it.

(14) After a predetermined period of time (usually selected to be a number of months) the walls of the channel (4) will have been dissolved/consumed/weakened by the deactivating agent. The integrity of the walls is therefore lost and the deactivating agent comes into contact with the explosive composition. The deactivating agent then causes crystallisation of the emulsion explosive composition thereby rendering it safe. Tests in a typical chart configuration (10 mm diameter cavity in a 57 mm diameter charge) indicate that a commercially available seismic emulsion explosive (Magnagel; Orica) can become insensitive to a No. 8 detonator 1 g PETN based charge within a month of exposure to a deactivating agent (Petra AG Special Liquid; Akzo Nobel).

(15) Although not shown in FIG. 1 the lower end of the cartridge (1) may also be shaped in order to be inserted into the detonator-receiving channel of an adjacent cartridge. Thus, forming like cartridges into a train of cartridges can also result in release of deactivating agent from the chamber (3) in which it is originally contained. The upper and lower ends of the cartridge (1) may also contain cooperating features, such as screw threads, to enable cartridges to be secured together.

(16) In the embodiment described when released the deactivating agent flows into channel (4) running essentially the entire length of the explosive composition included in the cartridge (1). This is a preferred arrangement and the volume of the cavity is configured to be such that in use it will contain sufficient deactivating agent to deactivate the entirety of the explosive composition (over time). After the wall of the channel (4) has been broken down by action of the deactivating agent, explosive composition adjacent to the deactivating agent and thus adjacent to the detonator when positioned in the cartridge will be first exposed to the deactivating agent. This region of the explosive composition therefore comes into contact with the highest concentration of deactivating agent thereby promoting the fastest and most effective deactivation of the explosive composition. Other arrangements are of course possible.

(17) In an alternative arrangement the deactivating agent flows into an annular cavity provided in the outer periphery of the cartridge body. In this embodiment it will be appreciated that the degradable material is provided on the outer surface of the emulsion preventing contact between the explosive composition and the deactivating agent (when released). When the material is degraded by the deactivating agent, the deactivating agent will contact outer regions of the explosive charge first. However, assuming the cartridge is used with a detonator in a central detonator-receiving passage, this embodiment suffers the potential drawback that explosive composition far removed from the location of the detonator will be deactivating agented first. There is therefore a greater risk of failure to deactivate the explosive composition if the deactivating agent action does not penetrate radially into the explosive composition (towards the location of the detonator). This embodiment does however have the advantage of a high surface area of contact between the deactivating agent and explosive composition.

(18) As a further alternative, the deactivating agent may flow into a cavity provided over the top of the body of explosive composition provided in the cartridge. However, this embodiment suffers the potential disadvantage of low surface area of contact between the deactivating agent and explosive composition and this can lead to slow and/or incomplete deactivation of the explosive composition. Other alternatives are of course possible within the context of the present invention.

(19) FIGS. 2 and 3 illustrate another embodiment of the present invention. FIG. 2 illustrates an arrangement before release of the deactivating agent and FIG. 3 an arrangement when the deactivating agent is released. The Figures show an exploded view of only a portion of the cartridge.

(20) FIGS. 2 and 3 show an explosive cartridge (1) in the form of an elongate cylinder made of a suitably rigid plastic. The cartridge includes a sealed chamber (2) containing an explosive composition and a further sealed chamber (3) containing a deactivating agent. During storage and transport of the cartridge (1) the deactivating agent and explosive composition remain sealed in their respective chamber (2,3).

(21) The cartridge (1) also includes a small diameter axial channel (4) extending down within the body of the cartridge (1) from the deactivating agent chamber (3) through the explosive composition. This channel is provided off-centre and is distinct from the channel into which a detonator (5) is provided. The walls of the channel (4) may be formed of a porous material that in use will allow deactivating agent to be communicated to the explosive composition and that has sufficient structural rigidity to define a channel adjacent or through the explosive composition.

(22) At the top (entrance) to the channel (4) there is an arrangement that is designed to cause release of deactivating agent from chamber (3) into the channel (4) when the cartridge (1) is to be used. This arrangement includes an elongate element (7) projecting upwardly from the top of the channel (4). This element (7) may be a tube that is adapted at one end to pierce a correspondingly located (rubber) seal (8) provided on the lower end of the deactivating agent chamber (3). The element (7) communicates at its lower end with a seal (9) provided over the entrance to the channel (4). This seal (9) is made of a material that is degradable on contact with the deactivating agent.

(23) Prior to use the seal (8) is in tact and the seal (8) and element (7) are in close proximity to each other. This arrangement is shown in FIG. 2. In use of the cartridge, the deactivating agent chamber (3) is displaced downwards relative to the element (7) and this occurs as a result of engagement of the upper end of the cartridge (1) with an engagement member (10). In the embodiment shown the inner surface of the upper end of the cartridge (1) includes screw threads adapted to engage corresponding screw threads provided on the outer surface of the engagement member (10). The member (10) may be a specially designed cartridge cap or the lower end of another cartridge (1). The action of screwing the member (10) into the top of the cartridge (1) causes the deactivating agent chamber (3) to be displaced downwards. In turn this causes the piercing element (7) to pierce the (rubber) seal (8). Deactivating agent then flows down through the element (7) thereby coming into contact with the degradable seal (9). This is shown in FIG. 3. As already noted, an air inlet or breather tube may be required to ensure flow of the deactivating agent, and surface tension effects may need to be taken into account too. Preferably, the air inlet/breather tube is activated only when the member (10) is screwed into the top of the cartridge (1) in order to release the deactivating agent. This prevents leakage of deactivating agent prior to use.

(24) After a predetermined period of time the seal (9) will be dissolved/consumed/weakened by the action of the deactivating agent. The integrity of the seal is lost thereby allowing deactivating agent to drain into the channel (4). The deactivating agent then flows through the porous/permeable walls of the channel and into contact with the explosive composition. The deactivating agent goes on to desensitise the explosive composition thereby rendering it safe.

(25) FIG. 11 shows an explosive cartridge (1) useful in implementation of the invention. The cartridge 1 includes explosive composition (11) which typically is in a solid (cast) form, such as Pentolite (typically a PETN/TNT and/or RDX mix). The explosive composition (11) includes detonator receiving channels (6) that enable the cartridge to be initiated by different sized (diameter) detonators. The cartridge (1) includes an outer shell (12) that is made of a water-permeable or water-degradable material. In the field environmental water may permeate or degrade the shell. The shell (12) also defines passages (13) extending into the explosive composition (11). The use of this configuration and type of shell allows environmental water to come into contact with the explosive composition (11), and is thus useful in embodiments of the invention where this is intended/required. The explosive composition (11) includes a chemical deactivating agent. For example, the chemical deactivating agent may be distributed throughout the explosive composition (11) in the form of pellets or granules. the pellets/granules may be mixed with the explosives composition (11) before the composition (11) is poured (cast) into the outer shell (12).

(26) Additionally or alternatively the chemical deactivating agent may be provided within the material making up the outer shell (12).

(27) FIG. 12 shows another form of an explosive cartridge (1) useful in implementation of the invention. The cartridge (1) includes an explosive composition (11), such as a cast Pentolite explosive, surrounded by a shell (12). Chemical deactivating agent may be provided as described in relation to FIG. 1. The shell (12) is water-permeable or water-degradable, as for the shell discussed in FIG. 11. In FIG. 12 the shell (12) includes radial members (14) extending into the bulk of the explosive composition. The intention here is that when the cartridge (1) comes into contact with water, water dissolves the shell (12) so that water is then conveyed into contact with and through the explosive composition, as required by certain embodiments of the invention described herein. The rate at which the shell (12) dissolves may be controlled by suitable selection of material used to form the shell (12).

(28) The material making up the shell (12), passages 13 and/or radial members 14 may be formed of a material that may be degraded by the action of microorganisms. As the shell (12) is degraded this allows water present in the environment to contact the chemical deactivating agent provided in the explosive composition (11) or shell (12). In turn this renders the chemical deactivating agent suitably mobile and/or active so that the chemical deactivating agent can commence desensitisation of the explosive composition. The microorganisms may also have the effect of acting on the explosive composition to convert it into less detonable or non-detonable by-products and/or by-products that are more environmentally friendly.

(29) FIG. 13 shows and explosive cartridge (1) suitable for use in seismic exploration. The cartridge (1) includes an explosive composition (a) and deactivating agent (b) in respective chambers (2,3). The chamber for the explosive composition (a) is in the form of a cylindrical shell comprising wall portions (2) sealed by a base (2). The explosive composition (a) may be Pentolite, possibly in mixture with RDX and/or aluminium particles.

(30) The explosive composition (a) and deactivating agent (b) are separated in their respective chambers by a base plate (14) that is loosely fitted at the lower end of the chamber (3) for the deactivating agent (b). The plate (14) may be formed of any suitable material such as a polyester or polycarbonate. The plate (14) may be provided with a double-sided adhesive to allow it to be positioned and retained in placethe purpose of the plate is to prevent contact between the deactivating agent (a) and explosive composition (b). That said, depending upon the nature of the deactivating agent and explosive composition it may be possible to dispense with the plate (14) altogether.

(31) The cartridge (1) also includes two detonator receiving channels (5) extending into the explosive composition (a). The cartridge (1) also includes a cap (15) at one end. This cap (15) is sized and shaped to fit, for example by interference fit, into the shell housing the explosive composition.

(32) In practice the cartridge (1) may be provided as separate components that are assembled during loading of respective components and when used in the field. With respect to FIG. 13, one component may be integrally formed (by injection moulding of a plastics material) to include and define, the cap (15), the detonator receiving channels (5) and the chamber (3) for the deactivating agent (b) as illustrated in FIGS. 14 and 15. The base plate (14) and chamber/shell (2) for the explosive composition (a) are separate components. The chamber (2) is made up of a cylindrical tube comprising wall portions (2) and a base (2) that is attached at a lower end of the tube thereby sealing it.

(33) FIGS. 14 and 15 illustrate certain components shown in FIG. 13. Thus, FIGS. 14 and 15 show the cap (15), detonating receiving channels (5) and chamber (3) for the deactivating agent formed as a one-piece construction, for example by injection moulding of a suitable plastics material. The chamber (3) for the deactivating agent is sealed by a separate plate (14). The cap (15) comprises a circular wall portion (15a) with a lip (15b) that enables the cap (15) to be secured (by interference fit) into a suitably sized and shaped chamber in which an explosive composition is provided (not shown in FIGS. 14 and 15).

(34) The cap (15) is typically inserted into a tube forming. The wall portions (2) extend above and below the cap (15) once inserted and are adapted to allow attachment of other cartridges or a nose cone, for example by thread fitting. The internal surface of the wall portion (2) may include a lug or tab to engage the lip (15b) so as to maintain the cap (15) in position. The upper end of the cap (15) is open to allow for insertion of at least one detonator into respective detonator receiving channels (5). The end of the cap (15c) may be sealed with a suitably sized and shaped lid (not shown) or be formed in an injection moulding process. The cap (15) and/or wall portions (2) may include apertures to allow water to enter the explosive cartridge. As noted the wall portion (2) extending above the position of the cap (15) may receive the lower end of another explosive cartridge to form a train of cartridges. In this regard a surface (15c) of the wall portion (2) may be threaded to mate with corresponding threads provided on the outer surface and at the base of another cartridge. Cartridges may also be coupled by interference fit or by clip fasteners. The cap (15) may include apertures or grooves (not shown) in the side wall thereof extending through the circular wall portion (15a) and lip (15b) through which detonator leads may be passed after a detonator loading.

(35) The embodiment illustrated in FIGS. 13-15 may be implemented as follows. In the orientation shown in FIG. 15 the plate (14) is removed and deactivating agent inserted into the chamber (3). The plate (14) is then replaced thereby sealing the chamber (3). The seal is loose in the sense that the chamber (3) is not liquid tight. Still in the orientation shown in FIG. 15, a cylindrical tube defining the wall portions (2) of the chamber (2) for the explosive composition (a) is inserted over the cap (15) with the cap (15) being retained in place by interference fit between the wall portion (2) and cap lip (15b).

(36) An explosive composition, such as Pentolite, can then be poured into the open end of the tube, thereby surrounding the chamber (3) and detonator receiving channels (5). If Pentolite is used it is cast above its melting point and allowed to solidify. Solidification may result in the formation of cracks and fissures extending through the bulk of the explosive composition. This may be desirable as such cracks and fissures allow water to travel through the explosive composition, as may be desired. Once the tube has been suitably filled with explosive composition, and the composition solidified as might be necessary, a base (2) is attached to the open end of the tube. The base (2) and wall portions (2) may form a seal by interference fit, male-female screw threading or by clip fastening.

(37) In use the component so-formed is loaded with one or more detonators with the detonator leads being passed out of the cap (15) or upper part of wall portions (2) as noted. The top end of the cap (15) may itself be sealed using a lid made of water-degradable material (not shown).

(38) In the embodiment described it is intended that the deactivating agent is rendered mobile by water entering the chamber (3) around the edges of the plate (14). The plate may additionally or alternatively include apertures to allow water entry into the chamber (3). Additionally or alternatively, the wall portions of the chamber (3) may also include structures to allow water to enter the chamber (3) (the chamber (3) may itself be made of water-degradable material to facilitate water ingress). Water mobilises the deactivating agent and the mobilised deactivating agent may exit the chamber (3) for contact with explosive composition via the same (or different) route through which water entered the chamber (3).

(39) Water may find its way into the chamber (3) in one or a combination of more than one way, as follows.

(40) Where respective components are joined together, for example the wall portions (2) forming the chamber (2) and the cap (15) or the wall portions (2) and base (2), the joint may allow water ingress. In this case water would enter the chamber (3) around the plate (14) by migration through the bulk of the explosive composition. The composition must therefore allow water transport by the presence of artificial and/or intrinsic water transport structures.

(41) Additionally or alternatively, water may enter the explosive composition through the walls (2) and/or base (2) of the chamber (2). One or both of these components may include channels/apertures to allow water entry and/or one or both may be water-permeable or water-degradable. The exact configuration will depend upon the form of, and thus the containment needs, of the explosive composition.

(42) Additionally or alternatively, water may enter the chamber (3) via the cap (15). Thus, the cap (15) may include channels/apertures extending through the cap (15) and into the chamber (3), for example through an aperture between the inner surface (15c) and the chamber (3). The aperture may itself be sealed by a water-degradable material. Water may enter the cap (15) through loose fitting seals (between the cap (15) and cap lid or between the wall portion (2) and an adjacent cartridge when a train of multiple cartridges is assembled). The apertures/grooves for the detonator leads may also allow water to enter the cap. Apertures/grooves in the upper part of the wall portions (2) may also allow water ingress.

(43) One or more components of the cartridge may be water-degradable, and the degradability may be selective in order to provide enhanced control with respect to intended deactivation of the explosive composition.

(44) Irrespective of the way in which water enters the chamber (3), when the deactivating agent is mobilised it will exit the chamber (3) and contact the explosive composition, thereby commencing deactivation of the explosive composition.

(45) Embodiments of the present invention are now illustrated in the following non-limiting examples.

EXAMPLE 1

(46) This example was undertaken to assess the effect as deactivating agent of a number of 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.

(47) TABLE-US-00001 TABLE 1 Class Material Details Water Water (test control) soluble 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 Propar 32 paraffin oil (test control) soluble Galoryl 626 10% solution in Propar 32 Galoryl 640 10% solution in Propar 32 Polar Ethane-1,2-diol Pure liquid organic Polyethylene glycol 600 Pure liquid liquids 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

(48) Teric GN8 is a 10% solution of nonylphenol ethoxylate oligomer with 8 ethoxylate units, commercially available from Orica.

(49) Petro AG Special Liquid is a 50% solution of sodium alkylnaphthalene sulphonate, commercially available from Akzo Nobel.

(50) The screening test involved providing a 20 ml layer of the reagent under test on top of 30 g of a typical emulsion explosive composition provided in a 100 ml glass beaker. The composition of the emulsion explosive composition is given in Table 2 below.

(51) TABLE-US-00002 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.

(52) 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 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 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).

(53) 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 illustrated in FIGS. 2, 3 and 4, respectively.

(54) 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 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

(55) 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 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).

(56) As further indication of the efficacy of the using Petro AG Special Liquid, FIGS. 5 and 6 are photographs showing the effect of Petro AG Special Liquid on an emulsion explosive composition of the type identified in Table 2. In FIG. 5 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 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 3 cm in depth and the Petro AG Special Liquid approximately 1.5 cm. FIG. 6 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 Special Liquid is believed to be immediately apparent when one compares FIGS. 5 and 6 side-by-side. It will be noted that the level of emulsion composition has dropped by approximately 1 cm (effectively 33%). This shows that the Petro AG Special Liquid has had a significant impact on the integrity of the emulsion explosive composition.

(57) For comparison, the experiment was repeated using a commercially available detergent (Teric GN8). The results are shown in FIG. 7 at the commencement of the test and FIG. 8 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 FIGS. 7 and 8. 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 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 centimeters away from the interface and within the body of the emulsion explosive composition. The exact mechanism by which this crystallisation occurs is not well understood but this is not material to the invention.

EXAMPLE 3

(58) When actively mixed into an emulsion explosive composition (as per Table 2), as opposed to simple surface contact, about 3% by weight of Petro AG Special Liquid was required to cause enough crystallisation to render a 63 mm 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 shown in FIG. 9. This figure shows that 3% is the theoretical minimum amount of Petro AG Special Liquid that would need to available in a self-deactivating cartridge in accordance with the present invention.

EXAMPLE 4

(59) In the proposed explosive cartridge in accordance with the present invention there is no 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 sufficient to deactivate an emulsion explosive composition, paper-walled axial cavities (10 mm and 12 mm in diameter, respectively) were created inside 57 mm 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 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 10 mm cavity equates to 3% w/w of the charge while the 12 mm cavity equates to 5% w/w of the charge.

(60) 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. The results are shown in FIG. 10. This figure also shows a control in which no cavity/deactivating agent was used.

EXAMPLE 5

(61) 500 ml water was heated to 45 C. in a water bath. Pentolite was added to 200 ppm (200 mg/L), consisting of 70 ppm PETN and 130 ppm TNT. Sodium hydroxide solution (0.004 M) was added in an amount of 0.2 ml 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.

(62) TABLE-US-00003 TABLE 3 PETN TNT (mg/L) (mg/L) NaOH (0.004M) 40 1.0 Water 45 110

(63) 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.

(64) 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.

(65) The action of alkali on TNT is well established in the art for destruction of TNT. It has, 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.

(66) This demonstration of the conversion of TNT in a Pentolite solution confirms that an alkali can be used to enhance the degradation of explosive devices, including Pentolite based devices.

EXAMPLE 7

Iron Degradation Control

(67) 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 particles may be maintained in a non-functional state until NaCl is released, thus initiating degradation of the Pentolite.

(68) Experimental

(69) Iron powder (Cat. no. 00631, Fluka, Australia) (150 mg) was added to 3 ml RNW buffer (1 mM KHCO.sub.3, 0.5 mM CaCl.sub.2, 0.206 mM MgSO.sub.4, 8.95 M FeSO.sub.4, 0.25 mM HCl, pH 7.8). To one set of iron containing tubes NaCl was added at 3 mM whilst a non-iron containing control was established with only RNW and 3 mM NaCl. The reaction commenced with the addition of Pentolite (acetone) solution to a final concentration of 100 ppm. Sacrificial sampling was performed for analysis after 1, 15 or 51 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.

(70) 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 increases in a time-dependent manner and is initiated by the presence of a corrosion enhancer.

(71) TABLE-US-00004 NaCl mediated degradation of Pentolite by Iron powder Time PETN TNT PETN % TNT % Sample (days) (mg/L) (mg/L) degradation degradation Control RNW 1 31.2 64 0% 0% 15 33.2 68 0% 0% 51 35.2 59.6 0% 0% Iron 1 31.2 64 0% 0% 15 52 68 0% 0% 51 36 60 0% 0% Iron + NaCl 1 31.2 64 0% 0% 15 32 21.2 3.6%.sup. 68.8% 51 15.2 <0.4 56.8% >97%

EXAMPLE 7

Iron Degradation Control

(72) 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.

(73) Experimental

(74) Iron powder (Cat. no. 12311Reidel-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.sub.3, 0.5 mM CaCl.sub.2, 0.206 mM MgSO.sub.4, 8.95 M FeSO.sub.4, 0.25 mM HCl, pH 7.8) to make a 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.

(75) 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.

(76) TABLE-US-00005 Degradation of Pentolite by iron wet form, but not dry form Time PETN TNT PETN TNT Sample (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 37.6 77.2 0% 0% 10 34.8 65.2 0% 0% Wet iron 3 2.8 0.4 92% 99% 10 1.2 <0.4 96% >99%

EXAMPLE 8

Degradation of PETN (SPC)

(77) 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 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).

(78) Experimental

(79) 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 alkalinity (1 mM KHCO.sub.3, 0.5 mM CaCl.sub.2, 0.206 mM MgSO.sub.4, 8.95 mM FeSO.sub.4, 0.25 mM HCl, pH 7.8). Two ten-fold serial dilutions were made of this solution into the same buffer, representing 10 mM and 1 mM SPC. A Pentolite (acetone) solution was added to 200 ppm in a volume of 3 mL per reaction and incubated at room temperature overnight in the dark. Samples were sacrificed by addition of 9 mL acetonitrile and TNT/PETN were analysed by HPLC-UV using standard methods.

(80) TABLE-US-00006 Degradation of Pentolite by sodium percarbonate PETN TNT PETN % TNT % Sample (mg/L) (mg/L) Degradation degradation Control 59.2 119.6 .sup.0% 0% 1 mM SPC 57.6 102.8 2.7% .sup.14% 10 mM SPC 53.6 2.8 9.5% 97.7% 100 mM SPC 10 <0.4 83.1% >99.7%

(81) 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.

(82) 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.