AU5200900A - Method of manufacturing an explosive composition - Google Patents

Description

WO 00/78695 PCT/AUOO/00681 METHOD OF MANUFACTURING AN EXPLOSIVE COMPOSITION The present invention relates to a non-detonable fluid composition and to a method of manufacturing said composition. The invention further relates to an explosives 5 composition based on the non-detonable fluid composition and to a method of manufacturing such an explosives composition. The invention relates yet further to a method of loading a blasthole and to a method of blasting. Explosives compositions, such as emulsion explosives compositions, are typically formed 10 by sensitising otherwise non-detonable fluid compositions comprising fluid energetic materials. However, the transportation of sensitised explosives is subject to considerable regulatory restriction and cost and the provision of a non-detonable fluid composition requiring little explosive sensitisation at the mining site would therefore be desirable. It would be of particular advantage to provide a non-detonable composition which requires 15 the minimum amount of processing at the blast site in order to sensitise it. In one aspect, the present invention seeks to provide such a non-detonable fluid composition. When a mass of earthen material is blasted, all the external dynamic loads are supplied by pressurised gas which is produced in the blastholes by the detonation of explosive charges. 20 Lateral gas pressure, acting progressively on fresh parts of a blasthole wall, creates waves which propagate away from the blasthole and reflect from nearby free faces. The complex wave fields damage, fracture and fragment the earthen material. Eventually the gas vents from the blasthole, increasing the fracturing and fragmentation, and heaving fragments through the air. The explosive must release enough energy to carry out these tasks 25 satisfactorily. Modern blast practice demands explosives with high energy density as one means of expanding blasthole patterns for greater efficiency. High-energy density explosives are potentially cheaper than the alternative of drilling blastholes with bigger diameters or drilling a large number of more closely spaced blastholes. 30 In soft media such as overburden or coal, efficient blasting also requires that the energy should be released relatively slowly, implying low velocities of detonation. If the WO 00/78695 PCT/AUOO/00681 -2 detonation proceeds too fast, energy will be wasted in creating excessive fines close to the blasthole. The desired explosive for blasting soft media therefore combines high energy density with a low velocity of detonation. 5 Conventional explosives compositions tend to exhibit moderate energy density, relatively low density and high velocities of detonation. The present invention seeks to provide explosives compositions which exhibit high energy density, relatively high density and low velocity of detonation. Further, the invention provides explosives compositions in which the velocity of detonation may be controlled with negligible or minimal influence on 10 energy density. Accordingly, the present invention provides a fluid composition which comprises a fluid energetic material and a multiplicity of cavities dispersed therein, wherein the cavities have an average particle size of at least 3.5mm and wherein the total volume occupied by the 15 cavities is such that the fluid composition is non-detonable. As used herein, the term "non-detonable" means that the fluid composition of the present invention gives a negative result in the Koenen test, the Time/Pressure test and the UN Gap test for solids and liquids. These tests are well-known in the art and are, for instance, 20 described in United Nations, 1995, Recommendations on the Transport of Dangerous Goods - Manual of Tests and Criteria, second revised edition, United Nations Publication, New York. The Koenen test is intended to determine the sensitivity of solid and liquid substances to the effect of intense heat under high confinement. The Time/Pressure test is used to determine the effects of igniting a substance under confinement in order to 25 determine if ignition leads to a deflagration with explosive violence at pressures which can be attained with substances in normal commercial packages. The UN Gap test is intended to measure the ability of a substance, under confinement in a steel tube, to detonate by subjecting it to detonation from a booster charge. 30 In these tests a negative (or fail) result, where the substance under test fails to respond to application of the prescribed stimuli is indicative that the substance is non-detonable. The WO 00/78695 PCT/AUOO/00681 -3 tests are recognised internationally as the standard tests for classification of explosive materials by all national competent authorities. The cavities present in the non-detonable fluid composition of the present invention have 5 an average particle size of at least 3.5 mm. Mixtures of cavities having different sizes may be used provided the average particle size satisfies this requirement. The cavities usually have an average particle size in the range of from 3.5 to 12mm, more preferably 4 to 8 mm. In practice of the invention cavities having an average particle size of 4, 6 or 8 mm are conveniently used. 10 The shape of the cavities is not critical, although essentially spherical cavities are convenient. The definition of the particle size of irregularly shaped cavities is difficult. However, a cavity may be considered to have an effective size for compression by considering various elements of the cavity. The cavity will be understood to have a 15 particle size of at least 3.5mm where at least a part of the cavity has a minimum dimension in every direction of at least 3.5 mm. It is preferred that the at least part of the cavity has a minimum dimension in every direction in the range of from 3.5 mm to 12 mm, more preferably from 4 to 8 mm. 20 The multiplicity of cavities having a dimension of at least 3.5 mm may be provided by multivoid particles. Multivoid particles may comprise cellular voids within plastic, carbonaceous, cellulosic or mineral materials. The cavity provided by the multivoid particles shall be considered to be the volume from which the fluid composition is excluded. 25 It is preferred that the multivoid particles comprise a fuel as the materials of construction thereof. Such multivoid particles which comprise a fuel include material such as cork, balsa wood, coke or the like. It is particularly preferred that the multivoid particles comprise expanded polymeric foams, such as polystyrene, polyurethane, polyethylene, 30 polypropylene, polyvinylchloride, polybutadiene rubber, or copolymers of these materials. Most preferably the multivoid particles are expanded polystyrene or polyurethane foam.

WO 00/78695 PCT/AUOO/00681 -4 Other multivoid particles which comprise a fuel include carbohydrate expanded organic fuels such as popcorn, puffed rice and puffed wheat. Multivoid materials which employ non-fuel materials may also be used in the present 5 invention and include expanded porous rock or other expanded salicaceous materials. Such materials include pearlite, vermiculite and fly ash. The cellular structure of the multivoid materials is preferably such that the multivoid material has a high proportion of closed cells. The thickness of the walls of the cellular 10 structure is preferably sufficient to prevent the collapse of the cellular structure prior to and during the incorporation of the multivoid materials into the fluid composition. However, the walls should be sufficiently thin to so as to enable the cells to be ruptured during the detonation of the fluid blasting agent. 15 The cavities typically have a density of 0.3 g/cc or less, for instance, 0.1 g/cc or less. In an embodiment of the invention, the density of the cavity is 0.02 g/cc or less, for instance about 0.009 g/cc. Foamed materials such as polystyrene typically have densities as low as this. The density of such materials will in part depend upon the extent to which the foamed material is expanded. 20 As noted above, the total volume (voidage) occupied by the cavities, based on the total volume of the fluid composition, is such that the material is non-detonable. Amongst others things this critical volume will depend upon the average particle size and the density of the individual cavities. The critical volume for a given type or types of cavity may be 25 determined by reference to the tests mentioned above. The volume occupied by the cavities is usually less than about 10% by volume based on the volume of the fluid composition. Thus, the fluid composition of the invention usually includes a small volume of relatively large sized cavities. For instance, the voidage may 30 be from 3 to 8% by volume.

WO 00/78695 PCT/AUOO/00681 -5 The % voidage provided by the cavities may be calculated using the following equation: V =d, -d x 100 where V is the voidage of the cavities based on the total volume of the composition, di is the density of the fluid composition prior to addition of the cavities and d 2 is the density of 5 the fluid composition when the cavities are present. In other words, the voidage is calculated based on the theoretical maximum density of the fluid composition. Although linked to cavity density and the volume occupied by the cavities, the cavities usually make up less than 0.15% w/w of the non-detonable fluid composition, for instance, 10 the amount may be less than 0.1% w/w, preferably from 0.05 to 0.1% w/w of the non detonable fluid composition. With low density cavities (density of about 0.009 g/cc or less) the amount of cavities is usually about 0.075% w/w. The most commonly used cavities are expanded (foamed) polystyrene particles having an 15 average particle size of from 4 to 8 mm and a particle density of less than about 0.009 g/cc. It is then typical that the quantity of such multivoid particles present in the composition is about 0.075% w/w based on the total weight thereof. The fluid energetic material used in the present invention is itself non-detonable and may 20 be any material which when appropriately sensitised may be detonated thereby causing an explosive blast. The fluid energetic material may be a liquid energetic material comprising oxidiser and fuel molecules homogeneously mixed, forming a non-detonable matrix. For instance, it may be a liquid material produced by molecular scale mixing of known oxygen releasing agents with organic fuel materials in a common aqueous/non-aqueous solvent. 25 This means it may be a concentrated aqueous or non-aqueous liquid. It may be a solvent diluted explosive material forming a non-detonable energetic liquid. Furthermore, it may be an eutectic material of oxidisers with fuels or their melts. It may also be an emulsion matrix comprising discontinuous an oxygen releasing salt component dispersed in an organic medium forming a continuous phase, or vice versa, stabilised by emulsifier. This 30 may embrace compositions of water-in-oil or oil-in-water emulsions. Preferably, the fluid WO 00/78695 PCT/AUOO/00681 -6 energetic material is in the form of a water-in-oil emulsion, melt-in-oil emulsion or melt in-fuel emulsion. For the sake of convenience the invention will now be described with reference to water-in-oil type emulsions although it will be apparent that the advantages described will be applicable to the other fluid energetic materials. 5 Suitable oxygen releasing salts for use in the aqueous phase of the emulsion include the alkali and alkaline earth metal nitrates, chlorates and perchlorates, ammonium nitrate, ammonium chlorate, ammonium perchlorate and mixtures thereof. The preferred oxygen releasing salts include ammonium nitrate, sodium nitrate and calcium nitrate. More 10 preferably the oxygen releasing salt comprises ammonium nitrate or a mixture of ammonium nitrate and sodium or calcium nitrates. Typically the oxygen releasing salt component of the emulsion comprises from 45 to 95 % w/w, and preferably from 60 to 90 % w/w, of the total emulsion composition. In 15 compositions in which the oxygen releasing salt comprises a mixture of ammonium nitrate and sodium nitrate the preferred composition is from 5 to 80 parts of sodium nitrate for every 100 parts of ammonium nitrate. Therefore, in the preferred composition the oxygen releasing salt component comprises from 45 to 90 % w/w (of the total emulsion composition) ammonium nitrate or mixtures of from 0 to 40 % w/w, sodium or calcium 20 nitrates and from 50 to 90 % w/w ammonium nitrate. Typically the amount of water employed in the emulsion is in the range of from 0 to 30 % w/w of the total emulsion composition. Preferably the amount employed is from 4 to 25 % w/w and more preferably from 6 to 20 % w/w. 25 The water immiscible organic phase of the emulsion comprises the continuous "oil" phase of the emulsion composition and is the fuel. Suitable organic fuels include aliphatic, alicyclic and aromatic compounds and mixtures thereof which are in the liquid state at the formulation temperature. Suitable organic fuels may be chosen from fuel oil, diesel oil, 30 distillate, furnace oil, kerosene, naphtha, waxes such as microcrystalline wax, paraffin wax and slack wax, paraffin oils, benzene, toluene, xylenes, asphaltic materials, polymeric oils WO 00/78695 PCT/AUOO/00681 -7 such as the low molecular weight polymers of olefines, animal oils, vegetable oils, fish oils and other mineral, hydrocarbon or fatty oils and mixtures thereof. Preferred organic fuels are liquid hydrocarbons generally referred to as petroleum distillates such as gasoline, kerosene, fuel oils and paraffin oils. 5 Typically, the emulsifier of the emulsion comprises up to 5 % w/w of the emulsion. Higher proportions of the emulsifying agent may be used and may serve as supplemental fuel for the composition but in general it is not necessary to add more than 5 % w/w of emulsifying agent to achieve the desired effect. Stable emulsions can be formed using relatively low 10 levels of emulsifier and for reasons of economy it is preferable to keep the amount of emulsifying agent used to the minimum required to form the emulsion. The preferred level of emulsifying agent used is in the range of from 0.1 to 3.0 % w/w of the water-in-oil emulsion. 15 In accordance with the present invention, the non-detonable fluid composition may be sensitised to form a detonable explosives composition. This is achieved by inclusion of a sensitising agent. It is believed that the sensitising reactions depend on the number of relatively small size hotspots. Adiabatic compression of the hotspots by shockwaves causes sensitising reactions to occur. The interactions between numerous thermal 20 explosions enable the propagation of the detonation wave by supplying the necessary chemical energy to the shock wave. In accordance with the present invention it is desirable that the non-detonable fluid composition is sensitised by the addition of the minimum amount of sensitising agent. The 25 minimum amount of sensitising agent which is used is that which has the effect of just sensitising the fluid composition. In other words, the volume of cavities present in the composition is advantageously very close to the critical volume at which the cavities would themselves sensitise the non-detonable composition. The use of small amounts of sensitising agent is beneficial in terms of cost and ease of preparation of the explosives 30 compositions and has implications in terms of achieving a low velocity of detonation. As a general rule, the inclusion of higher volumes of sensitising agent will increase the observed WO 00/78695 PCT/AUOO/00681 velocity of detonation. By varying the relative proportion of cavities and sensitising agent, the velocity of detonation may be controlled and tailored. Usually, the volume ratio of cavities to sensitising agent is about 70:30 to 55:45, more typically about 65:35. 5 In the sensitised explosives compositions, the total voidage, i.e. the voidage provided by the relatively large cavities and the voidage provided by the sensitising agent usually does not exceed about 15% by volume. Typically, the total voidage will be from 7 to 12% by volume. In practice, the total voidage provided by the sensitising agent is usually less than about 5% by volume, for instance less than 3% by volume. It is preferable to sensitise the 10 non-detonable fluid composition to form an explosive composition with (void) agents having a size of 30 to 300 microns, preferably 100 to 200 microns, more preferably 150 to 200 microns. Suitable sensitising agents include self explosives but preferably include a discontinuous 15 phase of small void agents. Suitable small void agents include glass or plastic microballoons, expanded polymeric (e.g. polystyrene) beads and gas bubbles, including bubbles of nitrogen generated in situ by chemical gassing agents and entrained air. Mixtures of these agents may be used. Chemical gassing is the most preferred means of sensitizing the non-detonable fluid energetic material. 20 The resultant sensitised explosives compositions in accordance with the present invention may have high energy densities but relatively low velocity of detonation. The velocity of detonation of the compositions is usually in the range 40 to 70%, for instance 50 to 60%, of the ideal (theoretically calculated) velocity for a given explosives composition. It is 25 believed that the voidage and nature of the voidage in the explosives compositions of the present invention is influential on the velocity of detonation observed. The volume strength of the explosives composition is usually greater than that of straight ANFO. A further interesting aspect of the compositions of the invention is that relatively low 30 velocities of detonation may be observed even when the compositions are detonated under strong confinement. Usually with emulsion explosives there is a relationship between WO 00/78695 PCT/AUOO/00681 -9 charge diameter and velocity of detonation. Smaller charge diameters tend to provide lower velocities of detonation. As charge diameter increases, so does the velocity of detonation. At infinite charge diameter, the maximum velocity of detonation would be observed. Explosives which have a velocity of detonation that varies with confinement are 5 said to exhibit non-ideal detonation behaviour. Steel pipe of 60-70 mm diameter and 5mm thick is considered to be strong confinement and detonation velocities obtained under such confinement conditions may be taken as representative of ideal, maximum values. It has been found that explosives compositions 10 in accordance with the present invention exhibit surprisingly low velocity of detonation under such strong confinement. Furthermore, it has been found that the velocity of detonation observed may be independent of charge confinement. The non-detonable fluid composition of the present invention may be formed conveniently 15 at a central manufacturing facility and, in the case of ammonium nitrate based materials, at or adjacent to an ammonium nitrate plant. Other facilities, such as mobile manufacturing units may also be employed with advantage to form the fluid energetic material. In general terms the composition is formed by dispersing the cavities in a fluid energetic material until a suitable voidage is achieved. The non-detonable fluid composition is usually 20 prepared in advance and then transported to on-site where it is sensitised before blast-hole loading takes place. The multiplicity of cavities may be dispersed in the fluid energetic material at the site at which the fluid energetic material is formed and then, as the resulting composition is non 25 detonable, be transported to the blast sites. The fluid composition may transported by any convenient and permissible means. Suitable means for transport include standard tankers for the transport of fluids, rubber bladders and the like. Preferably the transport includes a suitable pump for the transfer of the non-detonable fluid composition. The fluid energetic material used in the composition may be manufactured by any convenient means, either 30 before or during the dispersing of the multiplicity of cavities therein.

WO 00/78695 PCT/AUOO/00681 - 10 For mixing light, porous cavities in a relatively high viscosity fluid, the equipment which may be used includes: 1. High Speed Pin Blenders or Mills 5 2. Single or Duplex Paddle Blenders 3. Various Ribbon Blenders 4. Stirring Pots 5. Stationary Mixing Devices 10 The feeding of the light, porous cavities into mixing equipment may be achieved by augers or other volumetric feeders. In many instances it is advantageous to utilise the weighing belts mass feeding. Pneumatic air conveying methods are also possible. The explosives compositions of the present invention may be formed by a dispersal of 15 sensitising agent in the non-detonable fluids composition. This may be achieved by any of the conventional means. In a particularly preferred embodiment, the fluid energetic material, fluid composition or subsequently sensitised explosives composition may have incorporated therein additional 20 energetic materials to control the energy output of the ultimate explosive composition. It is preferred that the incorporation of additional energetic materials be at the blast site, at or about the time at which the non-detonable fluid composition is sensitised. The energetic material may have an impact on the energy density of the explosives composition and on the velocity of detonation observed. The energy density will typically increase and the 25 velocity of detonation typically decrease. This should be taken into account when an additional energetic material is included. It is preferred that the fluid energetic material or fluid composition and, in particular, water-in-oil emulsions are mixed with substances which are oxygen releasing salts or 30 which are themselves suitable as explosive materials. For example, a water-in-oil emulsion may be mixed with prilled or particulate ammonium nitrate and/or ammonium nitrate/fuel WO 00/78695 PCT/AUOO/00681 - 11 oil mixtures and/or finely divided aluminium. It is preferred that prilled ammonium nitrate having a particle size in the range of from 2 to 12 mm, preferably 2 to 5 mm in diameter be used. When ammonium nitrate is used the amount present is usually less than 40% by weight, for instance, from 10 to 30% by weight, based on the total weight of the 5 formulated explosives composition. In another aspect the present invention provides a method of loading a blasthole comprising the steps of: a) sensitising a non-detonable fluid composition, as described herein, to form an explosives 10 composition; and b) loading the explosives composition into the blasthole. The method of loading a blasthole in accordance with the present invention permits the mixing and delivery of the blasting agent by providing rapid and efficient mixing of the 15 sensitising agent (e.g. gassing solution) and, when required, energising materials into the non-detonable fluid composition. Sensitisation, when by in situ generation of gas, may be completed after the product is loaded into the blasthole. The sensitised explosives composition may be loaded into the blasthole by any convenient 20 means. Sufficiently fluid blends may be pumped by pumps such as progressive cavity pumps, rotary lobe pumps (rubber rotor) through plastic or rubber hoses of various diameter/length depending on type of boreholes or applications. The thicker and drier blends may be augured into the boreholes. It may also be possible to load by gravity utilising the concrete mixer type trucks. 25 The present invention provides an explosives composition whereby the rate of energy release may be controlled by the incorporation of the multiplicity of cavities and voids as described above. It is particularly advantageous that the rate of energy release be controlled so that the explosives composition may be tailored to suit the particular 30 geological environment in which the blast is to occur. This enables the explosives WO 00/78695 PCT/AUOO/00681 - 12 composition to be manufactured to more particularly meet the geological blast pattern design and customer requirements. Advantageously, the non-detonable fluid composition of the present invention has a predisposition to detonate at very low velocities of detonation. This may be achieved by inclusion of a small voidage of relatively large 5 volume cavities and subsequent sensitisation with a small voidage of relatively small sensitising agent. Additionally, it is possible to vary the total energy output of the explosives composition of the present invention whilst maintaining a low velocity of detonation. This may be 10 achieved by varying the proportion of energising solids which are incorporated prior to sensitisation. The solid energising materials such as ammonium nitrate and/or ANFO and/or aluminium as described above may be employed to increase the total energy. It has been found that the use of larger, porous particles of ammonium nitrate may obtain further reductions in velocity of detonation. 15 The present invention further provides a method of blasting which comprises detonating an explosives composition described herein. The composition may be detonated by conventional means. 20 The present invention will now be described with reference to the following non-limiting examples. Examples 1 and 2 25 A water-in-oil emulsion was prepared by blending components in the weight percentages shown below. Oxidiser Solution: Ammonium nitrate 74.82 Water 18.80 Acetic acid 0.28 WO 00/78695 PCT/AUOO/00681 - 13 Thiourea 0.05 Soda ash 0.05 Fuel Blend: Emulsifier 1.46 Paraffin oil 4.54 The emulsion formed had a density of 1.35 g/cc. 5 Non-detonable fluid compositions in accordance with the present invention were then prepared by dispersing cavities in the emulsion. In Example 1 the cavities were expanded polystyrene particles having an average particle size of 7 mm. The density of the resulting composition was 1.28 g/cc which corresponds to a voidage of 5.19%. In Example 2 the 10 expanded polystyrene particles had an average particle size of 4 mm. The density of the resulting composition was 1.26 g/cc corresponding to a voidage of 6.67%. The fluid compositions were then subjected to the Koenen, Time/Pressure and UN Gap tests. The results are given below. 15 Example 1 Example 2 Koenen Test Negative. Negative. No reaction. (Series 2) No reaction (Series 1) Time/Pressure Negative. Negative. Test No bursting of disc. No disc bursting UN Gap Test Negative. Negative. 260 mm pipe unfragmented. 290 mm pipe unfragmented. Witness plate domed. (Series 1) Witness plate domed. (Series 1) [The Series 1 and 2 tests include minor variations in test apparatus. These variations are documented].

WO 00/78695 PCT/AUOO/00681 - 14 These results show that the fluid compositions in accordance with the present invention are non-detonable. They may therefore be categorised as "not UN Dangerous Goods Class 1" Example 3 5 Compositions in accordance with the following table were prepared. The composition of sample no. 1 was a water-in-oil emulsion having the composition shown above. To this formulation was blended cavities of expanded polystyrene having an average particle size of 4 mm and/or sensitising agent in the form of glass microspheres or gas bubbles of 0.03 10 0.20 mm diameter. Detonation of each composition was attempted by use of a commercial primer (400g Anzomex) and the velocity of detonation (VOD) recorded where detonation was observed. The velocity of detonation of the compositions was measured utilising an optical fibre 15 method. In this method two lengths of optical fibre with clean cut ends were inserted a known distance apart (typically 100mm) into the explosive under test in a steel pipe. The other ends of the optical fibres were connected to the terminals of an electric timer which is capable of timing light pulses which are generated at the detonation front of the tested explosive, from a start and stop signal. The optical fibre located in the explosive charge 20 closest to the detonator provides the start signal for the timer. The second optical fibre at a known distance (100mm) stops the timer. The timer times the light pulse from the detonation front as it passes the start and stop optical fibres and displays the time in milliseconds. The velocity of detonation is calculated form the time taken for the detonation front to pass from the first to the second fibre. 25 The density of the formulations, voidage, confinement conditions and detonation results are shown in the following table. Sample No. Density Voidage (%vol) Charge diameter VOD (g/cc) 4mm 0.03 - 0.20 mm steel confinement (km/s) (mm) 1 1.35 - - 60 fail 2 1.28 - 5.2 60 6.00 WO 00/78695 PCT/AU00/00681 - 15 3 1.30 3.7 - 70 fail 4 1.29 4.4 - 70 fail 5 1.27 5.9 - 70 fail 6 1.25 7.4 - 70 fail 7 1.26 3.7 3.0 70 3.33 8 1.25 4.4 2.3 70 4.08 9 1.24 5.9 3.0 70 4.35 10 1.21 7.4 3.0 70 4.20 The same experiments were repeated using expanded polystyrene particles having an average particle size of 7 mm. The results are shown in the following table. Sample No. Density Voidage (%vol) Charge diameter VOD (g/cc) 7mm 0.03 - 0.20 mm steel confinement (km/s) (mm) 11 1.28 - 5.2 60 6.00 12 1.32 2.2 - 60 fail 13 1.31 3.0 - 60 fail 14 1.29 4.4 - 60 fail 15 1.26 6.7 - 60 fail 16 1.28 2.2 3.0 60 3.03 17 1.25 3.0 4.4 60 3.77 18 1.26 4.4 2.3 60 3.60 19 1.22 6.7 2.9 60 4.60 5 The unadditised (voidless) material fails to detonate even when initiated by strong primer (Sample no. 1). 10 Fluid energetic materials which include a relatively low voidage of small voids (0.03 0.20 mm), but which do not include any expanded polystyrene particles, detonate at relatively high velocity of detonation (Sample nos. 2 and 11).

WO 00/78695 PCT/AUOO/00681 - 16 Fluid energetic materials with a relatively low voidage of large multivoid polystyrene particles failed to detonate when initiated by strong primer (Sample nos. 3-6 and 12-15). Fluid energetic materials with a low voidage of large multivoid polystyrene particles which 5 previously failed to detonate become detonable when a low voidage of small (0.03 - 0.20 mm) voids are added. The velocity of detonation then observed was relatively low (Sample nos. 7-10 and 16-19). This experimental work utilised charges in 60-70 mm diameter, 5 mm thick steel pipes. It 10 is generally accepted that such pipes are classified as ideal confinement, which affords the theoretical maximum velocity of detonation. Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood 15 that the invention includes all such variations and modifications which fall within its spirit and scope. The invention also includes all of the steps; features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features. 20 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 (17)

1. A fluid composition comprising a fluid energetic material and a multiplicity of cavities dispersed therein, wherein the cavities have an average particle size of at 5 least 3.5 mm and wherein the total volume occupied by the cavities is such that the fluid composition is non-detonable.

2. A composition according to claim 1, wherein the average particle size is 3.5 to 12 mm.

3. A composition according to claim 1 or claim 2, wherein the average particle size is 10 4 to 8 mm.

4. A composition according to any one of claims 1 to 3, wherein the cavities are in the form of multivoid materials.

5. A composition according to claim 4, wherein the cavities are formed of a foamed polymeric material. 15

6. A composition according to claim 5, wherein the polymeric material is polystyrene or polyurethane.

7. A composition according to any of the preceding claims, wherein the volume occupied by the cavities is less than about 10% by volume based on the volume of the composition. 20

8. A composition according to any of the preceding claims, wherein the fluid energetic material is a water-in-oil emulsion.

9. A composition according to claim 8, wherein the aqueous phase of the emulsion comprises an oxygen releasing salt and the oil phase comprises a fuel.

10. A method of manufacturing a fluid composition as defined in claim 1, which 25 comprises dispersing in a fluid energetic material a multiplicity of cavities which WO 00/78695 PCT/AUOO/00681 - 18 have an average particle size of at least 3.5 mm, wherein the total volume occupied by the cavities is such that the resultant fluid composition is non-detonable.

11. An explosives composition comprising a non-detonable fluid composition as defined in any one of claims 1 to 9 and a sensitising amount of a sensitising agent. 5

12. A composition according to claim 11, wherein the average size of the sensitising agent is 30 to 300microns.

13. A composition according to claim 11 or 12, wherein the sensitising agent is a glass or plastic microballoon, an expanded polymeric bead, a gas bubble or a mixture thereof 10

14. A composition according to any one of claims 11 to 13, wherein the total volume occupied by the sensitising agent is about 5% by volume based on the total volume of the composition.

15. A method of manufacturing an explosives composition as defined in claim 11, which comprises dispersing a sensitising agent in a non-detonable fluid 15 composition as defined in any one of claims I to 9.

16. A method of loading a blasthole, which comprises the steps of: a) forming an explosives composition by sensitising a non-detonable fluid composition to as defined in any one of claims 1 to 9; and b) loading the explosives composition into the blasthole. 20

17. A method of blasting which comprises detonating an explosives composition as defined in any one of claims 11 to 14.