AU2006235772B2 - Explosive composition - Google Patents

Abstract

P.\0PERUCC\SPECIFICATIONS\12851470 EXPLOSIVE COMPOSITION.doc-31/10/2006 An explosive composition comprising: at least 90% by weight of a particulate oxidiser salt; and 5 10% by weight or less of an emulsified fuel, wherein the emulsified fuel comprises from 8-35% by weight of a discontinuous aqueous phase, at least 60% by weight of a water immiscible organic fuel as continuous phase, and an emulsifier, wherein the emulsified fuel does not contain an oxidiser salt, 10 and wherein the discontinuous aqueous phase is present in the emulisified fuel as droplets having an average droplet size of 0.5-20jm.

Description

P/00/0 I I Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT (ORIGINAL) Name of Applicant: Orica Explosives Technology Pty Ltd, of I Nicholson Street, Melbourne, Victoria 3000, Australia Actual Inventor: Vladimir Sujansky Address for Service: DAVIES COLLISON CAVE, Patent & Trademark Attorneys, of 1 Nicholson Street, Melbourne, 3000, Victoria, Australia Ph: 03 9254 2777 Fax: 03 9254 2770 Attorney Code: DM Invention Title: "Explosive composition" The following statement is a full description of this invention, including the best method of performing it known to us:- P:\OPERUCC\SPECIFICATIONSUI285470 EXPLOSIVE COMPOSITION doc.31/10/2006 EXPLOSIVE COMPOSITION The present invention relates to explosive compositions and to the manufacture thereof. The invention also relates to the use of explosive compositions in accordance with the 5 invention in blasting operations with the intention of achieving a reduction in after-blast fumes. Blends of ammonium nitrate (AN) and fuel oil (FO) have been used for many years in the explosives industry. Such ANFO blends usually include prilled (particulate) ammonium 10 nitrate and diesel fuel in a weight ratio of approximately 94:6. ANFO is cheap and generally effective. However, its use has a number of shortcomings. One problem with the use of ANFO in blasting operations is that under certain conditions it can produce large amounts of yellow/orange fumes in the gases produced on detonation. 15 These fumes contain nitrogen oxides (NOX) as a result of incomplete reactions during detonation of the ANFO. Herein these fumes are termed "after-blast" fumes. These fumes are very undesirable from an environmental perspective and it would be advantageous to carry our blasting operations that are "clean" with respect to the products of detonation. 20 A variety of factors are believed to influence the production of after-blast fumes, including mining method, blast design and explosive formulation. The presence of weak overburden that reduces appreciably confinement of the explosive has in fact been identified as a primary factor affecting generation of after-blast fumes. Thus, cast-blasting using conventional ANFO explosive compositions is notorious in generating large quantities of 25 undesirable after-blast fumes. The use of long explosive columns that result in high hydrostatic pressures and shock pre-compression from adjacent blastholes will also decrease the likelihood of ideal detonation of ANFO explosive compositions due to a reduction in critical charge diameter. Water ingress into the explosive charge from the formation being blasted may also occur when there is a significant delay between loading 30 of a blasthole and firing of the charge. This can also result in non-ideal detonation and thus the production of after-blast fumes.

P.\OPERUJCC\SPECIFICATIONSIl2851470 EXPLOSIVE COMPOSITION doc-3 110/2006 -2 A variety of attempts have been made to remedy the problem of after-blast fume generation associated with the use of ANFO explosive compositions in blasting operations. Some efforts have involved manipulating the oxygen balance of the explosive 5 compositions, reducing the size of the prill component, improving the intimacy between the components of the composition and/or including specific additives aimed at reducing after-blast fumes (see US 4,907,368, US 5,608,185 and US 6,539,870, for example). Other efforts have focussed on improving the conditions in the blasthole, e.g. dewatering, or enhancing the water-resistance of the explosive composition. Efforts have also 10 concentrated on manipulation of blast design (see US 6,684,791, for example). Some attention has also focussed on the use of nitrogen-free explosives (see US 5,920,030, for example). There remains however the need to provide an alternate solution to the problem of after 15 blast fume generation associated with ANFO explosive compositions. In particular there remains the need to provide a solution that is simple and economical to apply. Surprisingly, in accordance with the present invention, it has been found that replacement of standard fuels typically used in ANFO formulations with fuels containing water results 20 in explosive compositions that have significantly reduced tendency to generate after-blast fumes on detonation. It has also been found that the use of water-containing fuels may result in explosive compositions that exhibit increased detonability. Accordingly, the present invention provides an explosive composition comprising: 25 at least 90% by weight of a particulate oxidiser salt; and 10% by weight or less of an emulsified fuel, wherein the emulsified fuel comprises from 8-35% by weight of a discontinuous aqueous phase, at least 60% by weight of a water immiscible organic fuel as continuous phase, and an emulsifier, 30 wherein the emulsified fuel does not contain an oxidiser salt, and wherein the discontinuous aqueous phase is present in the emulisified fuel as droplets P:\OPERUCC\SPECIFICATIONSI 2831470 EXPLOSIVE COMPOSITION dc.31/10/2006 -3 having an average droplet size of 0.5-20 m. In principle, the oxidiser salt used in the compositions of the invention may be any salt that provides oxygen during detonation of the composition. The salt may be selected form 5 ammonium nitrate, potassium nitrate and sodium nitrate, as are widely used in blasting compositions. Such compounds are readily available in particulate form. Invariably, however, the present invention uses ammonium nitrate prill as the particulate oxidiser salt, and the invention will be described in more detail with particular reference to this salt (abbreviated to AN). 10 Central to the present invention is the use of an emulsified fuel (water-fuel emulsion) having the characteristics described above. Without wishing to be bound by theory, it is believed that the presence of water in the fuel is critical to achieving a reduction in after blast fumes when the explosive composition is detonated. With conventional ANFO 15 compositions, in order to produce clean (non-NO, containing) detonation gases, the reactions occurring on detonation between the particulate AN and the fuel component must take place at relatively precise stoichiometric ratios, usually about 94:6 w/w (AN:FO). If the oxidiser salt to fuel ratio is less than stoichiometric, reactions occurring on detonation will favour production of CO. On the other hand, if the ratio is greater than stoichiometric, 20 the detonation reactions favour NO, generation. However, due to the natural repulsive tendencies between the hydrophilic (AN) and hydrophobic (FO) components it is difficult to achieve homogeneity and thus stoichiometry at a molecular level. Thus, even if very well mixed, it is not possible to guarantee that the detonation reactions will proceed in an ideal manner as required for generation of NOX to be avoided. The key to production of 25 clean detonation gases is believed to be chemical reduction of nitrate ions with consequential and associated oxidation of hydrocarbons. Decomposition of AN without (adequate) oxidation of fuel hydrocarbons leads to the formation of polluting NOX gases. The use of the emulsified fuel as described herein is believed to play a significant role in 30 positively influencing the detonation efficiency and speed of reaction in the detonation process. In other words, it is believed that the emulsified fuel promotes reaction between P :OPER\JCC\SPECIFICATIONSUI2851470 EXPLOSIVE COMPOSITIONdc-31/10/2006 -4 nitrate ions and the fuel component. Without wishing to be bound by theory, it is believed that under the influence of a detonation shock wave, there is rapid heating at the AN/emulsified fuel interface due to adiabatic compression of the void space present between AN particles. This dynamic loading causes fracturing of the AN particles and the 5 generation of high surface temperatures. In turn this results in rapid vaporisation of water in the fuel into steam, with correspondingly rapid volume expansion. This results in disintegration of the fuel phase into a large number of fuel-emulsifier fragments, and this leads to a multiplication of reaction sites at the surface of the AN. The fuel-emulsifier fragments created by vaporisation of the water are thought to exist-as clusters of fuel and 10 emulsifier, the surface of the clusters being covered with micelles of emulsifier that effectively reduce the hydrophobic character of the fuel component. In turn, this allows intimate contact between the clusters and the oxidiser salt, thereby enhancing reaction between these species. 15 Multiplication of ignition sites is believed to be responsible for easing of shock wave initiation associated with detonation. The effective increase in the surface area of AN in contact with the fuel phase is also believed to be responsible for an increase in the rate of detonation and thus a reduction in reaction zone length (critical diameter). This is also believed to contribute to the production of clean detonation gases. 20 Furthermore, the detonation reactions are believed to proceed at a rate that is limited by diffusion of reactive species between the AN and fuel. The presence of water (droplets) is believed to promote diffusion of these species by providing intimate contact between oxidiser and fuel molecules. 25 The emulsified fuel component of the explosive composition of the present invention is essentially a water-in-fuel emulsion, and the characteristics of this emulsion are important. Thus, the emulsified fuel contains from 8-35% by weight discontinuous aqueous phase. Usually, this is simply water. Preferably, the amount of discontinuous aqueous phase is 30 from 10-20%, more preferably from 12-18%, by weight based on the total weight of the emulsion component. The aqueous phase is present in the fuel as discrete droplets P3\OPER\CCISPECIFICATIONS\1 2851470 EXPLOSIVE COMPOSITION do.-3WjIM/26 -5 stabilised by an emulsifier. The relative proportions of oxidiser salt and emulsified fuel will vary depending upon the amount of aqueous phase present in the emulsified fuel. It is important to achieve a 5 suitable oxygen/fuel balance for the composition to have suitable detonation efficiency, and the amount of emulsified fuel to be used should be determined with reference to the amount of fuel component that will be contributed to the composition. Thus, a particular oxygen/fuel balance may be achieved using a relatively small amount of a high fuel content emulsified fuel or by using a larger amount of a lower fuel content emulsified fuel. 10 Typically, the weight ratio of oxidiser salt: fuel will be about 94:6. The amount of emulsified fuel to be used can be determined accordingly based on the aqueous content of the emulsified fuel. All of this said, the stoichiometric ratio for the components of the composition may be less critical with respect to achieving a desired blast outcome in terms of after-blast fumes due to the beneficial inclusion in the emulsion of water. 15 In the case of an emulsified fuel with a relatively high aqueous phase content (say 12% by weight or more), it may advantageous to compensate for the dilution effect on the fuel component by increasing the amount of emulsified fuel in the composition to more than 6% by weight. Alternatively, or additionally, the composition may be dosed with one or 20 more additives that will contribute to achieving the appropriate oxygen/fuel balance. By way of example, wood meal may be added to the composition, usually in an amount of about 2% by weight based on the total weight of the composition. It is also a requirement that the emulsified fuel does not contain any oxidiser salt. Water 25 in-oil emulsions that contain oxidiser salt dissolved in the discontinuous aqueous phase are well known. However, these tend to be highly viscous when compared with the oil (fuel) component of the emulsion. One consequence of this is that special handling equipment needs to be used. Such conventional water-in-oil emulsions are also relatively expensive substitutes for the fuel component. In contrast, the present invention uses emulsified fuels 30 that are free from oxidiser salts and that are therefore advantageous, at least in terms of viscosity. The relatively low viscosity allows easy penetration of the emulsified fuel into P:\OPERVJCC\SPECIFICATIONS\I2851470 EXPLOSIVE COMPOSITION doc-31/10/2006 -6 the internal spaces of the AN prill (prill porosity) and hence, more efficient mixing between oxidiser and fuel. This is very important from the point of view of achieving equimolar mixing of the oxidiser and fuel components. 5 The continuous phase of the emulsified fuel includes at least 60% of a water immiscible organic fuel. Any fuel conventionally used in formulating ANFO type explosive compositions may be used in practice of the invention provided that an emulsified fuel having the characteristics described herein may be prepared. The nature of the emulsifier that is used will also be influential in this regard and one skilled in the art would readily 10 appreciate this. Usually, the fuel is a petroleum distillate. Preferably, the fuel is diesel fuel oil. Beside fossil fuels such as diesel oil, it is also possible to utilise oils that are derived from plants. In particular, the use of oils of vegetable origin may be considered when other 15 factors, like availability of supply and economy are taken into account. The use of vegetable oils, such as canola, palm, soya bean, sunflower, peanut and olive oil as alternative fuels to fossil fuels dates back many years. Due to their chemical composition in regard to the content of mono-saturated oleic acid, 20 low level of saturated fatty acid and acceptable level of linoleic acid canola oil may be considered as an ideal substitute for the diesel oil. This is the main substitute for diesel oil in Europe. Other fuel materials suitable for substitution are palm, sunflower and soybean oils, which are economic and the major source of supply in other parts of the world. 25 In terms of substitution, depending on the factors as availability of supply, economy, material handling, manufacturing and the effect on ecology, the extent of substitution of diesel fuel may vary from a partial to complete replacement in the formulation. The major advantages of natural vegetable oils are their high calorific value and hence, 30 high energy density. The fuels are neither harmful, nor toxic to humans, animals, soils or water and are also easy to store, handle and transport. From the point of view of this P:\OPERUCC\SPECIFICATIONS\l2851470 EXPLOSIVE COMPOSITION do.31/10/206 -7 invention it further improves the positive effect on the environment. The viscosity of the vegetable oils varies with temperature and hence selection of the fuel will be determined on the basis of their melting points. In regard to petroleum-based 5 diesel, the viscosity also varies between summer and winter versions and the values of melting points are between - 5 to - 200 C. Table below shows melting points of vegetable oils that are suitable for the substitution of the diesel fuel. 10 Vegetable Oils Approx. melting point *C Coconut oil 25 Palm kernel oil 24 Palm oil 35 Olive oil -6 Castor oil -18 Peanut oil 3 Canola (Rapeseed) oil -10 Cottonseed oil -1 Sunflower oil -17 Soybean oil -16 Tung oil -2.5 Linseed oil -24 The emulsified fuel used in accordance with the present invention may be formulated by mixing the aqueous phase (usually water) and the fuel phase with a suitable emulsifier. As noted, conventional emulsifiers may be used in this regard. Typically, the emulsifier is an 15 ionic or non-ionic surfactant. The amount of emulsifier used will vary depending upon, amongst other things, the amount of aqueous phase to be included in the emulsified fuel and the average droplet size of the aqueous phase to be achieved. Typically, the amount of emulsifier will be 2% by weight or less, based on the weight of the emulsified fuel.

P.\OPERUCC\SPECIFICATIONS\12851470 EXPLOSIVE COMPOSITION doc-31/10/2006 -8 However, if necessary, the amount of emulsifier may as high as 5% by weight. Conventional techniques may be applied for emulsion manufacture. It should be noted however that there are a number of requirements that may influence formulation of the emulsion. 5 One requirement is that in the emulsified fuel the average droplet size of the discontinuous aqueous phase is from 0.5-20ptm. Preferably, the average droplet size is from 0.5-10tm, more preferably from 0.5-5 tm. The average droplet size may be determined by standard techniques, such as microscopic examination (direct or with photography), light scattering 10 techniques, light transmission methods, and instrumental techniques, such as counting using a Coulter counter instrument. In this regard it will be appreciated that the emulsified fuel used in practice of the present invention is different from so-called "microemulsions" that are characterised as having a 15 lower average droplet size (typically 0.lpm or less). Microemulsions generally require relatively large amounts of emulsifier (and additional co-emulsifier) in order to form a stable emulsion. It is also a requirement that the emulsified fuel has suitably low viscosity to ensure 20 handleability and most importantly, mobility to allow efficient penetration of the internal spaces of the AN prill. Generally, speaking the emulsion viscosity will be from 2-10 mm 2 /s at 40'C. Typically, the density of the emulsion will be 0.8-0.9 kg/l. The emulsified fuel used in practice of the invention must also be suitably stable. By this 25 is meant that the emulsified fuel must substantially maintain its integrity from production through to use. Obviously, this may depend upon the context of intended use. It is preferred however that the emulsified fuel is stable for a period of weeks or preferably months so that it may be stored and used as necessary. The stability of an emulsion may be assessed by reference to a parameter such as droplet size. If the initial average droplet 30 size changes significantly (by, say, 20% or so), it is reasonable to assume that emulsion breakdown is occurring.

P:\OPERIJCC\SPECIFICATIONSUl28$470 EXPLOSIVE COMPOSITION dc-31/I0/ -9 In a preferred embodiment of the invention the emulsion being used is a commercially available diesel fuel. Products of this type have been available since around the end of 2003 for use in diesel engines. Commercially available examples include Aquazole T M and 5 Aquadyn TM (both TotalFinaElf), PuriNOx TM (Lubrizol), and Aquadiesel TM (Shell). These are emulsified blends of diesel fuel, water and various proprietary additives to enhance stability and engine performance. Such additives tend to be included in trace (ppm) amounts and do not have any detrimental effect on performance of explosive compositions of the present invention. The use of such commercially available products is advantageous 10 since the products are stable and readily available. A reduction in NOx may be associated with use of these fuels in a diesel engine. However, the mechanism by which NOx is produced on combustion of the fuel in this context is fundamentally different from the mechanism by which after-blast fumes are generated on detonation of an ANFO-type blasting agent. The fact that such fuels are known to result in reduced NOx in a diesel 15 engine is therefore believed to be irrelevant in the context of the present invention. The explosive compositions of the invention may be manufactured by simple mixing of particulate oxidiser salt (invariably AN, as noted) with the emulsified fuel component. Mixing of the components may be undertaken using conventional equipment. Simple 20 auger mixing in a continuous or batch process may be employed, for example in a concrete/cement mixer. It is possible for the emulsified fuel to contain additional components to achieve a reduction in NOx, such as urea or silicon powder, as described in US 5,608,185 and US 25 6,539,870, respectively. It may also be beneficial to include aluminium powder, used alone or in combination. Such additives may lead to unexpected advantages in terms of reduction of after-blast fumes. If such components are to be included, they may be added to the emulsion during manufacture or added to a pre-formulated emulsion. 30 The explosive compositions of the invention are used in a conventional manner in blasting operations. That is the composition is loaded into a blasthole and initiated using P:XOPERUCC\SPECIFICATIONSII2851470 EXPLOSIVE COMPOSITION doc-3 I/10/206 - 10 conventional initiation means, for instance using a length of detonating cord and an explosives booster or primer means. In relation to manufacture and use of explosive compositions, it is important that the 5 mechanical action involved with these processes does not result in detonation. Explosive compositions in accordance with the present invention have been found to be insensitive when formulated and used based on conventional manufacturing and blasthole loading methodology and equipment. 10 The present invention also provides a method of blasting, which comprises loading a blasthole with an explosive composition as described herein and detonating the composition. The method may be especially well suited to a cast blasting operations where the overburden and thus the level of confinement of the explosive are likely to be weak. 15 The method may also be advantageously applied in porous, weathered and well-fractured rocks of the type where it is generally well-known to observe problems with after-blast fumes. There are also many different geological formations, such as those containing sandstone, soft rock, mud seams and water-locked boreholes, that will be prime candidates for application of the method of the invention. 20 In another embodiment the present invention provides a method of reducing after-blast fumes in a blasting operation which comprises using an explosive composition as described herein as explosive material. 25 The present invention may also be applied to blends of normal (water-in-oil) emulsion explosives with standard ANFO formulations (so-called heavy ANFOs). In this case the standard ANFO component would be replaced with an explosive composition of the present invention. In this case the amount of explosive composition of the invention is usually about 60-95% w/w with the remainder being conventional water-in-oil emulsion. 30 A reduction in after-blast fumes and an enhancement in detonation properties is also likely to be observed in this context.

P.\OPER\UCC\SPECIFICATIONS\l 2851470 EXPLOSIVE COMPOSITION doc-31/10/2006 Embodiments of the present invention are illustrated with reference to the following non limiting table and examples. 5 Table 1 below illustrates the typical components that will be present in a composition of the invention together with typical components present in comparative (conventional) explosives compositions. The compositions are formulated by mixing the components in a concrete mixer. The AN prill is added first and then followed up with the additional ingredients. Those ingredients are added in small proportions while the mixer was 10 operated. In the case of Comparative Example 2, the nitromethane was added first and then followed up with the addition of the Diesel Oil No2.

P.\OPER'JCC\SPECIFICATIONS\12851470 EXPLOSIVE COMPOSITION doc.31/0/2006 - 12 Table 1 INDREDIENTS ANFO- ANFO- ANFO Emulsified Fuel Standard Nitromethane Example 1 Comparative Example 1 Comparative Example 2 (%w/w) (%w/w) (%w/w) Ammonium 93.5 94.0 93.5 Nitrate Prill Emulsified Fuel* 6.5 - Diesel Oil No2** 6.0 4.5 Nitromethane -_- 2.0 TOTAL 100.0 100.0 100.0 *Emulsified Fuel Shell AquadieselTM 85%w/w Diesel Fuel, 13%w/w Water & 2% 5 proprietary additive **Diesel Oil No2 - BP Oil Australia Ltd ***Nitromethane (racing nitrofuel, Angus Chemical Co.) After allowing the blends to stand for a short time, the explosive compositions were loaded 10 into waxed cardboard cylinders of various diameters and lengths (of between 965 - 988 mm). The free flowing density of the examples was measured by weighing the cylinders and calculating the volumes. The bulk density of the charges varied between 0.83- 0.87 g/cc. (0.85 +-0.02 g/cc). 15 Example 1 Compositions prepared according to Table 1 above were submitted for a detonation test in various unconfined diameters. Charges were detonated using Pentolite primers that were initiated with a No8 industrial strength detonator. The velocity of detonation (VOD) of the 20 charges was measured by utilising a micro-timer unit and optical fibres. A comparison between the compositions of Example 1 and of Comparative Examples 1 and 2 are included in Table 2. This shows that the composition of Example I is fully detonable when loaded into relatively small-unconfined diameters.

P:\OPERIJCC\SPECIFICATIONSl 2851470 EXPLOSIVE COMPOSITION.do-31/10/2006 - 13 Table 2 Charge Initiation Diameter Charge ANFO ANFO ANFO (mm) Emulsified Fuel Standard Nitromethane Detonator & VOD (km/s) VOD (km/s) VOD (km/s) Pentolite Example 1 Comparative Comparative Primer _ r Example 1 Example 2 60 No8 & 250 1.48 / Failed Failed Failed 70 No8 & 390 1.68 Failed 1.43 / Failed 90 No8 & 390 2.37 1.46 / Failed 2.43 100 No8 & 390 2.66 1.64 /Failed 2.66 128 No8 & 390 3.03 2.78 3.16 167 No8 & 390 3.21 3.20 198 No8 & 390 - 3.27 3.43 250 No8 & 390 - 3.55 5 The ANFO Standard of Comparative Example I is not detonatable in unconfined diameters below 128 mm, while the nitromethane sensitised composition in Comparative Example 2 would not detonate below 90 mm respectively, as demonstrated in the following table. 10 Table 3 Shot Explosive Type Initiation Detonation Detonation @ VOD No Charge Failure @ Diameter (km/s) Detonator! Diameter (mm) _________________Primer (gr) (mm 1 ANFO- 60 70 2.37 EMULSIFIED FUEL No8&390 example 1 ____________ 2 ANFO- 100 128 2.78 STANDARD No8&390 comparative example _ 3 ANFO- 70 90 2.43 NITROMETHANE No8&390 Comparative example 2 The results clearly show that the composition in accordance with the present invention P \OPERUCCISPECIFICATIONSl 2851470 EXPLOSIVE COMPOSITION doc-31/10/2006 -14 (Example 1) detonates more efficiently without the need for confinement or a larger diameter loading. This is important in blasting operations where there is a poor and/or weathered ground and/or accidental loss of confinement. It is known that the loss of confinement is the greatest factor in the formation of unwanted nitrogen oxides. 5 To the contrary, the compositions of Comparative Examples 1 and 2 are not able to support detonation under poor confinement, and when there is an accidental loss of confinement they will lead to deflagration or failure. These processes are known to produce large quantities of nitrogen oxides. 10 Example 2 Compositions prepared according to Table 1 above were submitted for a detonation test in Waxed 100-mm diameter cardboard tubes. The charges were detonated using of Pentolite 15 primers and No8 detonators. In tests 3, 4 and 5 a number of detonators were grouped together in order to determine the minimum number of detonators that are capable of initiating the experimental samples. The results are summarised below. Table 4 20 Tes Charge Initiation Charge t Diameter Detonator/Primer ANFO ANFO ANFO No (mm) Emulsified Fuel Standard Nitromethane VOD (km/s) VOD (kns) VOD (km/s) Example 1 Comparative Comparative Example 1 Example 2 1 100 N8&250 2.66 1.84 Partial det* 2.66 2 100 N8& 120 2.71 Detonation 2.67 ____ __________ ailure 3 100 10x No8 2.50 - Detonation failure 4 100 6 x No8 2.33 - 5 100 3 x No8 Detonation I _failure * Part of the cartridge left undetonated P:IOPERUCC\SPECIFICATIONS1l2851470 EXPLOSIVE COMPOSITION doc.3 IIIO0 - 15 The results indicate that the ANFO Emulsified Fuel in Example 1 is initiated by 6x No8 industrial strength detonators, while the ANFO Standard (Comparative Example 1) failed to be initiated by a 250 gr Pentolite primer. The nitromethane sensitised ANFO, in Comparative Example 2, was initiated by a 120 gr of Pentolite. 5 The results in Tables 3 and 4 show that ANFO-Emulsified fuel in accordance with the present invention exhibits superior initiation sensitivity and detonability in comparison with a Standard ANFO formulation and even with nitromethane sensitised ANFO. 10 These results indicate that poor confinement, which is usually reflection of a weak over burden, porous, weathered and fractured rock, is not going to affect the propagation of detonation of the ANFO-Emulsified Fuel in accordance with the present invention in the boreholes. 15 Example 3 Table 5 below compares the detonation and after-blast fume results of Comparative Examples I and 2 with that of ANFO Emulsified Fuel in accordance with the invention, i.e. Example 1, when detonated in unconfined shots of various diameters. A qualitative 20 fume rating based on the colour of the fumes was given.

P:\OPER\JCCISPECIFICATIONS\Il2851470 EXPLOSIVE COMPOSITIONdoc-31/10/2006 -16 Table 5 Charge Initiation ANFO- ANFO- ANFO Diameter Charge Standard Emulsified Fuel Nitromethane (mm) Pentolite Comparative Example 1 Comparative (gr) Example I Example 2 VOD(km/s) Blasting VOD(km/s) Blasting VOD(km/s) Blasting Fumes Fumes Fumes 60 250 Failed v. heavy 1.48/Failed slight Failed medium 70 390 Failed v. heavy 1.68 v. slight 1.43/Failed medium 90 390 1.46/ Failed heavy 2.37 v. slight 2.43 slight 100 390 1.64/Failed heavy 2.66 v. slight 2.66 slight 128 390 2.78 medium 3.03 Clean 3.16 v. slight 167 390 3.20 slight 3.21 Clean - In general significant generation of nitrogen oxides fumes is observed in the Standard 5 ANFO (Comparative Example 1) when the charge fails to detonate properly or when there is a partial detonation, sometime referred to as deflagration. The detonating charges produced after blast fumes that were rated as somewhere between medium to slight with respect to nitrogen oxide generation. 10 With regard to the ANFO-Emulsified Fuel in accordance with the invention, there is a very slight evolution of after blast fumes in unconfined diameters below 100 mm. However, the rating is "clean" in diameters above 100 mm unconfined diameter. The nitromethane sensitised example composition (Comparative Example 2) produced improved after blast fumes when comparison is made with the Standard ANFO (Comparative Example 1). 15 Example 4 Further comparative examples using unconfined charges demonstrate that the ANFO Emulsified fuel in accordance with the invention (Example 1) performs very well in terms 20 of after-blast fumes. Under heavy initiation by a Pentolite primer, the after blast fumes are "clean" in terms of nitrogen oxides. Even under extremely weak initiation the fume P:\OPERUCC\SPECIFICATIONS\I2851470 EXPLOSIVE COMPOSITION.doc.31110/2006 - 17 evolution of nitrogen oxides is only very slight. The ANFO Standard, Comparative Example 1, produces heavy after blast fumes during deflagration and detonation failure when initiated by Pentolite primer. The nitromethane ANFO, Comparative Example 2, produces slight yellow colour in the after-blast fumes when initiated by a Pentolite primer. 5 Table 6 Charge Initiation ANFO- ANFO- ANFO Diameter Charge Standard Emulsified Fuel Nitromethane (mm) Comparative Example I Comparative Example ) Example 2 VOD Blasting VOD Blasting VOD Blasting (km/s) Fumes (km/s) Fumes (km/s) Fumes 100 250 1.84 partial heavy 2.66 clean 2.66 slight 100 120 Failed v. heavy 2.71 clean 2.67 slight 100 10x No8 - - 2.50 v. slight Failed slig ht 100 6xNo8 - - 2.33 v. slight - 100 3 x No8 - - Failed slight - 10 The qualitative rating of after-blast fume ranges is: Clean - no colour, light white-grey fume background Very slight - very slight tinge of yellow in parts of the white-grey fume background Slight - slight yellow-orange tinge in parts of grey fume background 15 Medium - yellow-orange colour spread through parts of the dark fume Heavy - distinct orange- brown fumes spread in many parts of the dark fumes Very heavy - very distinct red- brown fumes in most parts of the dark fumes P :OPERUCCISPECIFICATIONSl2851470 EXPLOSIVE COMPOSITIONdoc-31/0/2006 - 18 Example 5 In order to determine the behaviour of various explosive compositions (ANFO blends) under accidental metal-to-metal impact conditions the following experiments were carried 5 out in a drop weight test apparatus. The drop weight test is based on impacting a small sample of the composition under test by a 2.5 kg drop weight. The weight is dropped from a known height onto 12.7 mm diameter roller bearings. About 50 mg of the composition under test is inserted between two steel 10 bearings and 100-c alumina sand paper. The parameter to be determined is the height of fall at which a sufficient amount of impact energy is transmitted to the composition for it to initiate. The criterion for positive initiation is based on a visual observation of spark and smoke emanating from the test 15 composition. The impact test value is the minimum height at which there are 10 positive ignitions from 10 trial results. 20 The following table shows comparative results between an explosive composition of the invention and a standard ANFO blend. Table 7 Sample Number of tests Number of Drop height weight Ignitions (cm) (mg) ANFO 50 10 10 72.5 standard ANFO 50 10 10 80.5 emulsified fuel (invention) 25 P \OPER\JCC\SPECIFICATIONS\2851470 EXPLOSIVE COMPOSITION do.-31/102006 - 19 The results show that the explosive composition in accordance with the present invention is slightly less sensitive to impact than the ANFO Standard. The lower drop height value indicates greater sensitivity, while the higher drop value signifies less impact sensitivity. 5 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. 10 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.

Claims (14)

1. An explosive composition comprising: at least 90% by weight of a particulate oxidiser salt; and 10% by weight or less of an emulsified fuel, wherein the emulsified fuel comprises from 8-35% by weight of a discontinuous aqueous phase, at least 60% by weight of a water immiscible organic fuel as continuous phase, and an emulsifier, wherein the emulsified fuel does not contain an oxidiser salt, and wherein the discontinuous aqueous phase is present in the emulsified fuel as droplets having an average droplet size of 0.5-20pm.

2. The explosive composition of claim 1, which comprises from 10-20% by weight of the discontinuous aqueous phase.

3. The explosive composition of claim 2, which comprises 12-18% by weight of the discontinuous aqueous phase.

4, The explosive composition of any one of the preceding claims, wherein the discontinuous aqueous phase is water,

5. The explosive composition of the any one of the preceding claims, wherein the water immiscible organic fuel is a vegetable oil.

6. The explosive composition of claim 5, wherein the water immiscible organic fuel is canola oil.

7. The explosive composition of any one of the preceding claims, wherein the water immiscible fuel is diesel oil.

8. The explosive composition of any one of the preceding claims, which comprises - 21 5% by weight or less of the emulsifier.

9. The explosive composition of any one of the preceding claims, wherein the average droplet size is 0.5-10p±m.

10. The explosive composition of claim 9, wherein the average droplet size is 0.5-5.m.

11. The explosive composition of claim 1, substantially as hereinbefore described.

12. A method of blasting, which comprises loading an explosive composition as claimed in any one of claims I to 11 in a blasthole and detonating the explosive composition.

13. A method of reducing after-blast fumes in a blasting operation which comprises using an explosive composition as claimed in any one of claims 1 to 11 as explosive material,

14. The method of claim 12 or 13, substantially as hereinbefore described.