AU2018100464A4 - Misfire Marker. A device for increasing the visibility of misfired blast holes in tunnel blasting - Google Patents

Abstract

Patents Act 1990 INNOVATION PATENT MISFIRE MARKER The following statement is a list of the claims of this invention,: MISFIRE MARKER 1. When blasting tunnels for construction and mining it is not uncommon for blast holes to fail and leave remnant explosives in the rock mass. 2. These remnant explosives may be impact sensitive and provide a hazard to persons engaging in subsequent operations such as drilling and excavation. 3. Where misfires are identified they are able to be made safe. 4. Misfires may be difficult to identify owing to damage to the remnant explosives. Unidentified misfires are a significant hazard. 5. This invention relates to a visible marker that is loaded into every hole and, should the hole fail to detonate, provides a highly visible marker. 6. In the current embodiment the Misfire Marker consists of a highly visible tube loaded into the base of the hole. 7. Where the hole misfires the robust Misfire marker remains protruding from the remnant blast hole providing a highly visible indicator of a misfire. 8. The Misfire marker may also facilitate the removal of remnant explosives by providing an encapsulation of the remnant explosives. Figure 4. Section through a typical tunnel blast hole containing a Misfire Marker. Misfire Marker Hole Toe Hole Collar Explosives Primer (Explosives) Detonator

Description

MISFIRE MARKER 1. In tunnel blasting it is common for an array of blast holes to be drilled, charged with explosives and blasted in a defined sequence in order to increase the length of the tunnel. One common form of tunnelling is underground mine development where access tunnels are blasted to enable men and machinery to access the various parts of the mine. A typical mine development blast consists of between 30 and 60 drill holes in a defined array. (Figure 1 shows a typical arrangement of drill holes for a 5m high x 5m wide mine development tunnel). 2. A typical loaded blast hole in a tunnel is shown in Figure 2. This consists of a collar where the hole starts, a toe where the hole ends, a primer containing a detonator which is typically loaded near the toe of the hole and a charge of explosives. 3. After a tunnel blast is fired the broken material is excavated by machinery and the freshly excavated tunnel surface are supported using a variety of means to make the area safe for access by men and machinery. Common methods to support freshly excavated rock surfaces include rock bolts, steel mesh pinned to the rock mass and sprayed on shotcrete lining. 4. A significant issue when excavating a tunnel blast is the presence of misfired or undetonated explosives remaining in drill holes in the face. (Figure 3 shows an example of a misfire remaining after a tunnel blast has fired) Remaining misfires can contain impact sensitive explosives such as detonators and primers that can cause unplanned detonation during subsequent drilling, and other, activities. An unplanned detonation in the vicinity of men and machinery can cause serious injury and damage. 5. Where misfires are identified by personnel inspecting the area after a blast they are able to be recovered and made safe prior to any subsequent activity that may cause an unplanned detonation. Where misfires are hidden and are not able to be visibly identified they pose a significant risk as they are not recovered and remain the rock in a position that may be subject to impact from subsequent operations and cause an unplanned detonation. 6. This invention has been specifically designed to increase the visibility of misfired holes in order to ensure that undetonated explosives in tunnel blasts are identified and made safe prior to any subsequent activity being undertaken. 7. This invention, referred to as a 'Misfire Marker' consists of a highly visible tube, rod or tape which is attached to the primer at the base of the hole and extending towards the collar of the hole (Figure 4 shows typical examples of the arrange for placing a misfire marker in a tunnel blast hole). 8. Where a blast hole detonates properly the misfire marker is destroyed by the detonating explosives. Where the blast hole misfires and the explosives fail to detonate the misfire marker is not destroyed. In this situation either the misfire marker remains in the blast hole and provides a visible indication of the presence of misfired explosives or the misfire marker is dragged out of the hole by the movement of the blasted material and, owing to the misfire marker being attached to the primer, causes the primer to be drawn from the misfired blast hole. (Figure 5 shows the condition of a misfire marker in a misfired blast hole and Figure 6 shows a hole where the misfire marker has facilitated the extraction the impact sensitive primer). 9. In the current embodiment the Misfire Marker consists of a highly visible tube of a diameter slightly larger than the primer and of a length of between 300mm and 2,000mm. The tube is both fluted and slotted to provide a highly visible marker and to allow explosives to be loaded in and around the tube. The tube has one blind end to ensure the explosives primer is retained in the Misfire Marker 10. In other embodiments the Misfire Marker may consist of a flat tape, a rod or any variation of a linear marker extending from the primer toward the collar of the hole with the objective of providing a visible indicator of a misfire.

Claims (4)

1. MISFIRE MARKER CLAIMS

   1. A Misfire Marker consisting of linear device loaded into a blast hole designed to provide a visible indication of a blast hole that has failed to detonate.
2. 2. A Misfire Marker as claimed in claim 1 which is attached to the blast hole primer by means of a retention device that facilitates the retention of the Misfire Marker and the removal of any misfired primer.
3. 3. A Misfire Marker as claimed in claim 2 which extends from the toe of the blast hole or from the primer toward the collar of the blast hole
4. 4. A Misfire Marker as claimed in claim 3 consisting of a tube, flat or solid section extending from the toe toward the collar and being constructed of a material that is destroyed by contact with detonating explosives and is not completely destroyed when located in a blast hole which fails to detonate.