WO2003071219A2

WO2003071219A2 - Method of blasting coal

Info

Publication number: WO2003071219A2
Application number: PCT/IB2003/000629
Authority: WO
Inventors: Mark Rodney Davis
Original assignee: Van Der Walt, Louis, Stephanus
Priority date: 2002-02-21
Filing date: 2003-02-21
Publication date: 2003-08-28
Also published as: WO2003071219A3; AU2003207373A1; AU2003207373A8

Abstract

This invention relates to a method of blasting coal. The invention extends to an explosive for use in a method of blasting coal and, more particularly, to an explosive composition (14) which includes an explosive constituent (17) and a non-explosive inhibitor material (19). The invention further relates to a method of preparing an explosive charge and to a cartridge 10 for an explosive.

Description

AN EXPLOSIVE COMPOSITION AND A METHOD OF BLASTING COAL

THIS INVENTION relates to the control of explosive charge. More particularly, it relates to a method of blasting coal, to an explosive composition, to a method of preparing an explosive charge, to a cartridge for an explosive and to a cartridge casing.

According to one aspect of the invention, there is provided a method of blasting coal, which method includes the step of making use of an explosive which has a Relative Weight Strength of less than one hundred relative to fueled porous prilled ammonium nitrate (ANFO), at a density of 0.8 g/cm³, and an Absolute Strength Value (ASV) of less than ANFO, that is, of less than 3.8 MJ/kg.

Preferably, the explosive has a density of at least 1 g/cm³.

According to another aspect of the invention, there is provided a method of blasting coal, which method includes the step of making use of an explosive having a velocity of detonation (VOD) of less than 3 000 m/s.

The explosive may include a high explosive material. By "high explosive" is to be understood an explosive having a reaction rate sufficiently fast to generate and sustain a supersonic shock wave, i.e. an explosive which detonates, rather than deflagrates, and including, for example TNT, ANFO, heavy ANFO and emulsions.

According to still another aspect of the invention, there is provided an explosive for use in a method as hereinbefore described.

According to another aspect of the invention, there is provided an explosive composition which includes an explosive constituent; and a non-explosive inhibitor material.

By "inhibitor material" is to be understood a material which, upon detonation of the explosive constituent, serves to decrease a velocity of detonation and/or to reduce an energy of explosion of the explosive constituent, for example, by absorption of energy released during the explosion.

The composition may have a density of at least 1 g/cm ³.

The explosive constituent may have a density of less than 1 g/cm³. The non-explosive inhibitor material may have a density of greater than 1 g/cm³.

The inhibitor material may include a metal or metallic oxide or hydroxide . The inhibitor material may include an oxide or hydroxide of iron or tin. In a preferred embodiment of the invention, the inhibitor material is haematite. More particularly, the inhibitor material is in the form of crushed haematite ore. Typically, the crushed ore particles will have a diameter of not more than about 40 mm.

The explosive constituent may include an inorganic nitrogen-oxygen salt. The explosive constituent may include ammonium nitrate. More particularly, the explosive constituent may include a porous prilled ammonium nitrate (PPAN), such as, for example, that available from SASOL SMX under the trade mark "EXPAN 100". In this embodiment of the invention, the explosive constituent typically includes a fuel oil.

In another embodiment of the invention, the explosive constituent may include a fueled porous prilled ammonium nitrate. The explosive constituent may include a fueled porous prilled ammonium nitrate having a bulk density of between about 0.61 kgΛ! and about 0.70 kg/{, such as, for example, that available from SASOL SMX under the trade mark "EXPANFO".

The explosive composition may include between about 1 6 % by mass and about 89 % by mass explosive constituent. The explosive composition may include between about 1 1 % by mass and about 84 % by mass inhibitor material.

Where the explosive constituent is the fueled porous prilled ammonium nitrate available from SASOL SMX under the trade mark "EXPANFO" and the inhibitor material is haematite, the explosive composition may include about 53.6 % by mass fueled porous prilled ammonium nitrate (i.e. "EXPANFO") and about 46.4 % haematite.

According to another aspect of the invention, there is provided a method of preparing an explosive charge, which method includes the step of charging at least one cartridge casing with a mixture comprising an explosive and an inhibitor material.

The method may include the prior step of blending the explosive and the inhibitor material.

The method may include providing a plug of explosive material in at least one end of the or each cartridge casing. The method may include providing a plug of explosive material in each end of the or each cartridge casing. The or each plug of explosive material may taper inwardly away from the end of the cartridge casing. The explosive material may be an emulsion-type explosive.

The explosive may comprise ammonium nitrate and the inhibitor material may be a high density inert material.

The high density inert material may be an oxide or hydroxide of lead or tin.

According to yet another aspect of the invention, there is provided a cartridge for an explosive, which cartridge includes a tubular body defining a bore within which an explosive composition is receivable ; and at least one operatively inwardly tapering packing plug insertable into an end of the body.

The cartridge may include an explosive composition as hereinbefore described, received in the bore.

The cartridge may include at least one closure cap for closing an end of the body.

The at least one closure cap may be adhered to an outer surface of the body.

The or each plug may be generally conical and define an internal hollow. The cartridge may include an explosive contained within the hollow of the or each plug. The explosive contained in the hollow of the or each plug may be an emulsion-type explosive. Preferably, the cartridge includes two plugs, a plug being insertable into each end of the body.

The body may be of a synthetic plastics material, such as, for example, polyvinyl chloride (PVC) .

The body may be circular cylindrical and have an outer diameter of between about 50mm and about 1 50mm. More particularly, the body may have an outer diameter of about 75mm. The body may have a length of between about 300mm and about 2000mm. In a preferred embodiment of the invention, the body has a length of about 600mm. The body may have a wall thickness of between about 0.5mm and about 3.0mm. More particularly, the body may have a wall thickness of about 1 .5mm.

According to a further aspect of the invention, there is provided a cartridge for an explosive, which cartridge includes a tubular casing; an explosive composition contained within the casing; and at least one inwardly tapering packing plug inserted into an end of the casing.

The cartridge may include at least one closure cap for closing an end of the casing.

The or each plug may be generally conical and define an internal hollow. Preferably, the cartridge includes two packing plugs, a packing plug being inserted into each end of the casing. The cartridge may include an explosive contained within the hollow of the or each plug. The explosive contained in the or each plug may be an emulsion- type explosive.

The or each closure cap may be adhered to an outer surface of the casing.

The explosive composition may include an explosive constituent, and a non-explosive inhibitor material. The explosive constituent may include an inorganic nitrogen-oxygen salt, such as, for example, ammonium nitrate. More particularly, the explosive constituent may include a porous prilled ammonium nitrate (PPAN) . Typically, the explosive constituent will further include a fuel oil. In another embodiment of the invention, the explosive constituent may include a fueled porous prilled ammonium nitrate. The explosive constituent may include a fueled porous prilled ammonium nitrate having a bulk density of between about 0.61 kg/H and about 0.70 kg/ϋ, such as, for example, that available from SASOL SMX under the trade mark "EXPANFO".

Each cartridge may include about 48.4 % by mass explosive constituent. Each cartridge may include about 41 .9 % by mass inhibitor material.

According to still another aspect of the invention, there is provided a method of blasting coal, which method includes interconnecting a plurality of rigid explosive-containing cartridges thereby to form a continuous assembly of cartridges.

The method may include inserting the assembly into a blasting hole such that the assembly extends for at least part of the length of the hole. Preferably, the assembly extends for a greater part of the length of the hole.

Interconnecting the cartridges may include coupling complementary coupling formations defined at opposed ends of adjacent cartridges.

The cartridges may be as hereinbefore described. The explosive may be provided by an explosive composition as hereinbefore described.

The invention provides also a cartridge for an explosive, which cartridge includes a casing and at least one coupling formation defined on the casing for coupling the casing to another like cartridge casing.

The casing may include a priming aperture defined therein.

The cartridge may include at least one complementary coupling formation defined on the casing at a position spaced from the at least one coupling formation for coupling with the at least one coupling formation defined on another like cartridge casing to facilitate interconnection of the cartridge casings.

Preferably the cartridge casing and the coupling formations are configured to permit coupling of the cartridge casings in a stacked configuration. To this end, the coupling formation and complementary coupling formation may be provided on opposed surfaces of the cartridge casing.

The casing may include a tubular body defining a bore within which an explosive composition is receivable and at least one closure cap for closing an end of the body, the coupling formation being defined on the closure cap. The cartridge casing may include a plurality of complementary coupling formations located at spaced apart positions.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings.

In the drawings,

Figure 1 shows an axial section through a cartridge for an explosive in accordance with the invention;

Figure 2 shows an exploded plan view of the cartridge for an explosive of Figure 1 ; Figure 3 shows a perspective view of an apparatus for use in the preparation of an explosive composition forming part of the cartridge of Figure 1 ;

Figure 4A shows a side view of two interconnected cartridge casings in accordance with the invention; Figures 4B to 4D each show a bottom plan view of another cartridge casing of the invention and a side view of a top end of a complementary cartridge casing of the invention; and

Figure 5 shows a side view of a cartridge assembly of a method of blasting coal of the invention.

In Figure 1 of the drawings, reference numeral 10 refers generally to a cartridge for an explosive in accordance with the invention. The cartridge 10 includes a tubular circular cylindrical casing 1 2 manufactured from PVC piping. It will be appreciated, that the casing 1 2 may be of any suitable material, including, for example, other plastics materials or paper. An explosive composition 14 is contained within the casing 1 2. Each casing 1 2 has an inner diameter D of about 75mm and has a length L of about 600mm. Each casing has a wall thickness of about 1 .5mm.

The explosive composition 14 includes an explosive constituent as well as a non-explosive inhibitor material. The inhibitor material includes the oxide of iron, Fe₂O₃, in the form of haematite which has been pre-crushed into particles of not greater than about 40 mm in diameter. Other metals or metallic oxides or hydroxides may be used as the inhibitor material, such as, for example, lead, cassiterite, limonite and pyrite.

In one embodiment of the invention, the explosive constituent includes the inorganic nitrogen-oxygen salt of ammonium nitrate. In this embodiment of the invention, the explosive constituent may be the fueled porous prilled ammonium nitrate available from SASOL SMX under the trade mark "EXPANFO", which has a bulk density of between about 0.61 kg/0 and about 0.70 kg/{, a minimum of about 99.4% by mass ammonium nitrate, and a particle size distribution as follows: at most about 5% of the particles having a diameter of greater than 2.5mm and at most about 1 % of the particles having a diameter of less than 0.1 mm. Instead, the explosive constituent may include a porous pilled ammonium nitrate (PPAN) together with a fuel oil.

To prepare the explosive composition 14 for use, the porous prilled ammonium nitrate or fueled porous prilled ammonium nitrate 1 7, as the case may be, is placed in a first holding hopper 1 6 (Figure 3). The crushed haematite ore 1 9 is placed in a second holding hopper 1 8, the first and second holding hoppers 1 6, 1 8 having discharge ends which open into a common chute 20. A speed of rotation of an auger (not shown) of each hopper 1 6, 1 8 is preset to permit a blending of the ammonium nitrate constituent 1 7 and the haematite ore 19 in a desired ratio, and the augers are run so as to mix the constituents together thereby to form the explosive composition. Typically, the explosive composition includes between about 1 6% by mass and about 89% by mass explosive constituent (that is, PPAN or fueled porous prilled ammonium nitrate) and between about 1 1 % by mass and about 84% by mass inhibitor material. For blasting of coal the Inventor has found that an explosive composition including about 53.6% by mass fueled porous prilled ammonium nitrate available from SASOL SMX under the trade mark "EXPANFO" and about 46.4% by mass crushed haematite ore works particularly well.

Preparing the explosive composition may include sampling the density of the composition product 14 of the mixing and, if necessary, adjusting the auger speeds to change the ratio of mixing of the explosive and inhibitor components 1 7, 1 9, respectively, thereby to vary a density of the composition 14.

In the embodiment of the invention in which the explosive constituent is in the form of porous prilled ammonium nitrate, fuel oil is added to the explosive composition 14 in a quantity of about 6% by mass of the PPAN.

The explosive composition 14 is conveyed to a charging station (not shown) where a plurality of cartridge casings 1 2 (see Figure 1 ) are charged with the mixture comprising the explosive and the inhibitor material. About 2800g of explosive composition 14 may be accommodated within each cartridge casing 1 2.

A plug 24 (Figure 1 ) of an explosive material, such as, for example, an emulsion explosive (e.g . that available under the trademark "EXPLOGEL" from SASOL) or a molecular explosive, is inserted into each end 26 of the tubular cartridge casing 1 2. Each plug 24 tapers inwardly away from the end 26 of the cartridge casing 1 2. To this end, each plug includes a housing 28 which is generally conical and defines an internal hollow, which housing 28 is receivable in an end 26 of the casing 12 and within the hollow of which housing 28 the explosive material is receivable (see Figure 2). Each conical housing 28 typically has a length S of about 50 mm and can contain between about 140g and about 1 50g of explosive material. The Inventor believes that the plugs 24 of explosive material will, in use, ensure propagation of explosion from one cartridge 10 to another, when a cartridge 10 is set off in proximity to another cartridge 10. Furthermore, it is believed that the plugs 24, being of inwardly tapering form, will reduce the migration of particles of which the explosive composition 14 is comprised by virtue of different sizes, shapes and densities thereof, which migration arises as a result of vibrations acting on the cartridge 10 and its contents during packing and transportation of the cartridge 10.

The cartridge casing 1 2 includes two closure caps 30, 31 of a plastics material, each closure cap 30, 31 being snugly receivable over an end 26 of the casing 1 2 so as to seal off the contents of the casing 12 from an exterior of the casing 1 2/atmosphere. Each closure cap 30, 31 is adhered to an outer surface 32 of the casing 12 by use of a suitable adhesive. Each cap 30, 31 includes a central disc portion 70 and a circumferentially extending skirt portion 72 which depends therefrom and has a length of about 1 9 mm. The closure cap 31 further includes a circular cylindrical wall 74 which extends from the disc portion 70 from an opposed end thereof to the skirt portion 72 and which defines a seat in which a closure cap 30 of an adjacent cartridge casing 12 is removably receivable.

Closure caps 30, 31 define complementary coupling formations by which a casing 1 2 can be coupled to another adjacent casing 1 2. In a preferred embodiment of the invention, the cap 31 includes diametrically opposed radially outwardly projecting key formations 76 (see Figure 1 ) and wall 74 of cap 30 defines complementary opposed recesses 78 on an internal surface 80 thereof. It will be appreciated that the cap 31 is slidably receivable in the cap 30 when the key formations 76 are in register with the recesses 78, the two caps being relatively angularly displaceable in order to interlock two adjacent cartridge casings 12 bayonet-fashion. In another embodiment, three key formations 76 and recesses 78 are defined in the caps 31 , 30, respectively.

The cartridge for an explosive 10 is typically used during the blasting of coal in open-cast coal mining. The Inventor is aware, in the conventional blasting of coal, of the production of very fine coal (so- called "coal fines") as well as of large lumps of coal. In order to facilitate use of the latter in power stations, these large lumps of coal are to be crushed after blasting. Both unusable/unsaleable fines and larger lumps of coal requiring post-blasting crushing increase mining costs. The Inventor believes that the use of the explosive composition of the cartridge for an explosive 10 of the invention in the blasting of coal will improve fragmentation in blasting and permit controlled sizing of coal during blasting.

One of the most critical parameters in blasting is the so- called "powder factor", that is the ratio of explosive mass to rock volume. It is believed that the explosive composition of the invention will permit more optimized blasting of coal in that it provides an explosive which has a Relative Weight Strength of less than 100 (relative to fueled porous prilled ammonium nitrate (ANFO)) and an Absolute Strength Value of less than that of ANFO (i.e. of less than 3.8 MJ/kg) . The explosive composition 14 further has a velocity of detonation (VOD) of less than 3 000 m/s.

The haematite component of the explosive composition 14, having a density of greater than 1 g/cm³, provides a high density material which, when mixed with the fueled porous prilled ammonium nitrate "EXPANFO" (of density less than 1 g/cm³), renders the explosive composition 14 of average density greater than 1 kg/fi (or 1 g/cm³). It will be appreciated that a cartridge 10 containing the composition 14 will therefore sink in water where placed in a blasting hole which contains water.

The Inventor believes that the explosive composition 14 of the invention containing, as it does, an inhibitor material for dampening of explosion will provide an explosive of reduced power which, it is believed, in turn will yield coal fragments of more uniform size. Furthermore, it is believed that the cartridge form of the explosive of the invention will permit a user to control the sizing of blasted coal yielded by a reduction or enlargement of the size of the cartridge 10. Furthermore, controlled sizing of blasted particles may occur by varying the ratio of explosive to non-explosive constituent in the explosive composition 14. The Inventor believes that the explosive composition 14 forming part of the cartridge 10 of the invention will yield, in use, a dampened explosion whilst providing an explosive with a density of greater than 1 g/cm³ and thereby not compromising the ability of the cartridge 10 to sink in water. Furthermore, it is believed that the fueled porous prilled ammonium nitrate constituent of the explosive composition 14 of the cartridge 10 of the invention will serve to render the explosive composition 14 sensitive to initiation. The Inventor believes that the haematite constituent of the explosive composition 14 will reduce a velocity of detonation of the fueled porous prilled ammonium nitrate "EXPANFO" from about 3500m/s to about 2000m/s and hence reduce an energy of explosion of the explosive composition 14.

In use, a plurality of cartridges 10 are typically interconnected to form a continuous assembly of cartridges 10 (Figure 5) which is inserted into a blasting hole 90 so as to extend for a greater part of the length L of the hole 90. The explosive composition contents 14 of the cartridges 10 are therefore distributed along the length L of the hole 90, which, it is believed, further facilitates controlled sizing of blasted coal. A stemming material 93 (e.g . soil, stones, or the like) is typically placed in a mouth of the blast hole 90 to plug/stem the hole 90. As will be appreciated from Figure 5, an air cushion 92 may be inflated near a mouth of the hole 90 to plug the blast hole 90 and stemming material 93 may be placed on top of the cushion 92.

Reference is now made to Figures 4A to 4D of the drawings in which reference numeral 50 refers to a cartridge casing in accordance with the invention. The cartridge casing 50 includes a coupling formation 52 defined on a surface thereof for coupling the casing 50 to another cartridge casing 54. The cartridge casing 50 further includes a complementary coupling formation 56 defined on an opposed surface of the casing 50 to the coupling formation 52 for permitting coupling of the cartridge casing 50 to a casing 54 having a similar coupling formation 52, i.e. to facilitate interconnection of the cartridge casings 50, 54. The cartridge 50 includes a priming aperture (not shown) defined in a surface thereof, via which aperture initiation of the explosive material may take place. It will be appreciated that the coupling formations 52, 56 may be defined on closure caps of the cartridge casing 54.

In one embodiment of the cartridge casing 50 of the invention (Fig . 4A), the coupling formation 52 is in the form of a male dove tail formation, the complementary coupling formation 56 being in the form of a complementary dove tail-shaped recess, in which the coupling formation 52 of another casing 54 is slidably receivable. In the embodiment of the invention shown in Figure 4B, the coupling formation 52 is in the form of an arrow head shaped projection, the complementary coupling formation 56 being in the form of a slot of width slightly greater than a length of a tailing edge 59 of the arrow head formation 52, in which the slot 56, the projection 52 is snap- fittingly receivable. In the embodiment of the invention shown in Figure 4C of the drawings, the coupling formation 52 is in the form of a projection having a semi-spherical head 60 attached to a neck 62, an opposite end of which neck 62 is attached to the casing 50. In this embodiment of the invention, the complementary coupling formation 56 is in the form of a circular aperture defined in a surface of the casing 50, in which the head 60 is snap-fittingly receivable. In the embodiment of the cartridge casing 50 shown in Figure 4D, the coupling formation 52 is in the form of a frusto-conical projection, the complementary coupling formation 56 being in the form of circular inwardly-tapering recess in which the coupling formation 52 is press-fittingly receivable. It will be appreciated that the coupling formation and complementary coupling formation may take any suitable form and may provide, for example, a key-in-hole type arrangement, the coupling formation being slidably receivable in the complementary coupling formation in one orientation and being retained in the complementary coupling formation in another angularly displaced orientation.

If desired, complementary coupling formations 56 may also be provided at other positions on the cartridge casing.

In mining operations, a quantity of explosives required for blasting will vary with the magnitude of size of the rock/mineral to be blasted, for example, during secondary blasting of large rock pieces yielded by the primary (main ore) blast. Accordingly, it is desirable to provide a means of varying a quantity of explosive with relative ease. The Inventor believes that the inter-connectable cartridge casings 50, 54 of the invention will facilitate the building up of a series of cartridge casings 50, 54 which cumulatively contain a required quantity of explosives. Furthermore, interconnection of the cartridges 50, 54 will provide a linkage of explosive both horizontally in two dimensions and vertically to achieve a desired surface cover, shape and/or height. It is believed that the cartridges 50, 54 will provide shaped charges which permit a priming of the explosive from a top thereof, thereby to yield a more effective explosion/blast. The cartridges 50, 54 of the invention provide for flexibility of use. It is believed that the cartridges 50, 54 of the invention will provide a safe means of packaging explosives and will lend themselves to a safe method of providing a desired quantity of explosive, dispensing with a need for the cutting of explosives to desired size.

Claims

CLAIMS:

1 . A method of blasting coal, which method includes the step of making use of an explosive which has a Relative Weight Strength of less than one hundred relative to fueled porous prilled ammonium nitrate (ANFO), at a density of 0.8 g/cm³, and an Absolute Strength Value (ASV) of less than ANFO, that is, of less than 3.8 MJ/kg.

2. A method as claimed in Claim 1 , in which the explosive has a density of at least 1 g/cm³.

3. A method of blasting coal, which method includes the step of making use of an explosive having a velocity of detonation (VOD) of less than 3 000 m/s.

4. A method as claimed in Claim 3, in which the explosive includes a high explosive material.

5. An explosive for use in a method as claimed in any one of

Claims 1 to 4, inclusive.

6. An explosive composition which includes an explosive constituent; and a non-explosive inhibitor material.

7. An explosive composition as claimed in Claim 6, which has a density of at least 1 g/cm³.

8. An explosive composition as claimed in Claim 6 or Claim 7, in which the explosive constituent has a density of less than 1 g/cm ³.

9. An explosive composition as claimed in any one of Claims 6 to 8, inclusive, in which the non-explosive inhibitor material has a density of greater than 1 g/cm ³.

10. An explosive composition as claimed in any one of Claims 6 to 9, inclusive, which includes between 16 % by mass and 89 % by mass explosive constituent and between 1 1 % by mass and 84 % by mass inhibitor material.

1 1 . An explosive composition as claimed in any one of Claims

6 to 10, inclusive, in which the inhibitor material includes a metal or metallic oxide or hydroxide .

12. An explosive composition as claimed in Claim 1 1 , in which the inhibitor material includes an oxide or hydroxide of iron or tin.

13. An explosive composition as claimed in Claim 12, in which the inhibitor material is haematite.

14. An explosive composition as claimed in Claim 1 3, in which the inhibitor material is in the form of crushed haematite ore.

1 5. An explosive composition as claimed in Claim 14, in which the crushed ore includes particles having a diameter of not more than 40 mm.

1 6. An explosive composition as claimed in any one of Claims

6 to 1 5, inclusive, in which the explosive constituent includes an inorganic nitrogen-oxygen salt.

1 7. An explosive composition as claimed in Claim 1 6, in which the explosive constituent includes ammonium nitrate.

1 8. An explosive composition as claimed in Claim 1 7, in which the explosive constituent includes a porous prilled ammonium nitrate.

1 9. An explosive composition as claimed in Claim 1 8, in which the explosive constituent includes a fuel oil.

20. An explosive composition as claimed in Claim 1 7, in which the explosive constituent includes a fueled porous prilled ammonium nitrate.

21 . An explosive composition as claimed in Claim 20, in which the fueled porous prilled ammonium nitrate has a bulk density of between 0.61 kg/ϋ and 0.70 kg/fi.

22. An explosive composition as claimed in Claim 20 or Claim 21 , which includes 53.6 % by mass fueled porous prilled ammonium nitrate and 46.4 % haematite.

23. A method of preparing an explosive charge, which method includes the step of charging at least one cartridge casing with a mixture comprising an explosive and an inhibitor material.

24. A method as claimed in Claim 23, which includes the prior step of blending the explosive and the inhibitor material.

25. A method as claimed in Claim 23 or Claim 24, which includes providing a plug of explosive material in at least one end of the or each cartridge casing.

26. A method as claimed in Claim 25, which includes providing a plug of explosive material in each end of the or each cartridge casing.

27. A method as claimed in Claim 25 or Claim 26, in which the or each plug of explosive material tapers inwardly away from the end of the cartridge casing.

28. A method as claimed in any one of Claims 25 to 27, inclusive, in which the explosive material is an emulsion-type explosive.

29. A method as claimed in any one of Claims 23 to 28, inclusive, in which the explosive comprises ammonium nitrate and the inhibitor material is a high density inert material.

30. A method as claimed in Claim 29, in which the high density inert material is an oxide or hydroxide of lead or tin.

31 . A cartridge for an explosive, which cartridge includes a tubular body defining a bore within which an explosive composition is receivable ; and at least one operatively inwardly tapering packing plug insertable into an end of the body.

32. A cartridge as claimed in Claim 31 , which includes an explosive composition as claimed in any one of Claims 6 to 22, inclusive, received in the bore.

33. A cartridge as claimed in Claim 31 or Claim 32, which includes at least one closure cap for closing an end of the body.

34. A cartridge as claimed in Claim 33, in which the at least one closure cap is adhered to an outer surface of the body.

35. A cartridge as claimed in any one of Claims 31 to 34, inclusive, in which the or each plug is generally conical and defines an internal hollow.

36. A cartridge as claimed in Claim 35, which includes an explosive contained within the hollow of the or each plug.

37. A cartridge as claimed in Claim 36, in which the explosive contained within the hollow of the or each plug is an emulsion-type explosive.

38. A cartridge as claimed in any one of Claims 31 to 37, inclusive, which includes two plugs, a plug being insertable into each end of the body.

39. A cartridge as claimed in any one of Claims 31 to 38, inclusive, in which the body is of a synthetic plastics material.

40. A cartridge as claimed in any one of Claims 31 to 39, inclusive, in which the body is circular cylindrical and has an outer diameter of between 50mm and 1 50mm.

41 . A cartridge as claimed in Claim 40, in which the body has an outer diameter of 75mm.

42. A cartridge as claimed in any one of Claims 31 to 41 , inclusive, in which the body has a length of between 300mm and 2000mm.

43. A cartridge as claimed in Claim 42, in which the body has a length of 600mm.

44. A cartridge as claimed in any one of Claims 31 to 43, inclusive, in which the body has a wall thickness of between 0.5mm and 3.0mm.

45. A cartridge as claimed in Claim 44, in which the body has a wall thickness of 1 .5mm.

46. A method of blasting coal, which method includes interconnecting a plurality of rigid explosive-containing cartridges thereby to form a continuous assembly of cartridges.

47. A method as claimed in Claim 46, which includes inserting the assembly into a blasting hole such that the assembly extends for at least part of the length of the hole.

48. A method as claimed in Claim 46 or Claim 47, in which interconnecting the cartridges includes coupling complementary coupling formations defined at opposed ends of adjacent cartridges.

49. A method as claimed in any one of Claims 46 to 48, inclusive, in which the cartridges are cartridges as claimed in any one of Claims 31 to 45, inclusive.

50. A method as claimed in any one of Claims 46 to 49, inclusive, in which the explosive is provided by an explosive composition as claimed in any one of Claims 6 to 22, inclusive.

51 . A cartridge for an explosive, which cartridge includes a casing and at least one coupling formation defined on the casing for coupling the casing to another like cartridge casing.

52. A cartridge as claimed in Claim 51 , in which the casing includes a priming aperture defined therein.

53. A cartridge as claimed in Claim 51 or Claim 52, which includes at least one complementary coupling formation defined on the casing at a position spaced from the at least one coupling formation for coupling with the at least one coupling formation defined on another like cartridge casing to facilitate interconnection of the cartridge casings.

54. A cartridge as claimed in Claim 53, in which the at least one coupling formation and at least one complementary coupling formation are provided on opposed surfaces of the cartridge casing.

55. A cartridge as claimed in any one of Claims 51 to 55, in which the casing includes a tubular body defining a bore within which an explosive composition is receivable and at least one closure cap for closing an end of the body, the at least one coupling formation being defined on the closure cap.

56. A cartridge as claimed in any one of Claims 51 to 55, which includes a plurality of complementary coupling formations located at spaced apart positions.

57. A method of blasting coal as claimed in Claim 1 or Claim 3, substantially as herein described and illustrated.

58. An explosive as claimed in Claim 5, substantially as herein described and illustrated.

59. An explosive composition as claimed in Claim 6, substantially as herein described and illustrated.

60. A method of preparing an explosive charge as claimed in Claim 23, substantially as herein described and illustrated.

61 . A cartridge for an explosive as claimed in Claim 31 or Claim 51 , substantially as herein described and illustrated.

62. A method of blasting coal as claimed in Claim 46, substantially as herein described and illustrated.

63. A new method of blasting coal, a new explosive/explosive composition, a new method of preparing an explosive charge or a new cartridge for an explosive, substantially as herein described.