In mining operations, the efficient fragmentation and breaking of rock by means of explosive charges demands considerable skill and expertise. In most mining operations explosive charges are planted in appropriate quantities at calculated positions in the rock. The explosive charges are then actuated via detonators with predetermined time delays, thereby providing the desired pattern of blasting and rock fragmentation. Typically, signals are transmitted to the detonators via non-electric systems employing low energy detonating cord (LEDC) or shock tube. Alternatively, electrical wires may be used to transmit signals to electric detonators. More recently, the use of electronic detonators has permitted the use of programmable time delays with an accuracy of 1 ms or less.
The establishment of the blasting arrangement, and the positioning of explosive charges, is often labour intensive and highly dependent upon the accuracy and conscientiousness of the blast operator. The blast operator must correctly position explosive charges for example within boreholes in the rock, and ensure that detonators (and optionally boosters) are brought into proper association with the explosive charges. Importantly, the blast operator must ensure that the detonators are in proper signal transmission relationship with a blasting machine, in such a manner that the blasting machine can transmit a FIRE signal to actuate each detonator, and in turn actuate each explosive charge.
Electronic blasting systems that involve direct electrical communication between the blasting machine and the detonators may permit the use of more sophisticated signaling. For example, such signaling may include ARM, DISARM, and delay time instructions for remote programming of the detonator firing sequence. Moreover, as a security feature, detonators may store firing codes and respond to ARM and FIRE signals only upon receipt of matching firing codes from the blasting machine.
To respond to such command signals, electronic detonator systems may comprise programmable circuitry that enables receipt, memory storage, and processing of the incoming signals. However, this programmable circuitry can itself present safety issues. For example, the power supply for the programmable circuitry may inadvertently trigger the firing circuitry of the detonator, resulting in unintentional actuation of the detonator base charge.
Systems and methods have been developed to help avoid the possibility of inadvertent detonator actuation by command signals received by the detonator, thereby improving the safety of the blasting arrangement. For example, U.S. Pat. No. 6,644,202 issued Nov. 11, 2003 discloses a method of establishing a blasting arrangement by loading at least one detonator into each of a plurality of blast holes, placing explosive material in each blast hole, connecting to a trunk line a control unit that has a power source incapable of firing the detonators, sequentially connecting the detonators, by means of respective branch lines, to the trunk line and leaving each detonator connected to the trunk line. In a preferred embodiment, the control unit includes means for receiving and storing in memory means identity data from each detonator, means for generating a signal to test the integrity of the detonator/trunk line connection and the functionality of the detonator, and means for assigning a predetermined time delay of each detonator to be stored in the memory means. In this way, the control unit can communicate with the detonators via a direct electrical connection (i.e. the trunk line). However, the power source in the control unit that enables the communication is too small to risk inadvertent detonator actuation.
Other improvements in the safety of blasting relate to the development of wireless detonators and corresponding detonator systems. Persons of skill in the art recognize the potential of wireless detonator systems for significant improvement in safety at the blast site. By avoiding the use of physical connections (e.g. electrical wires, shock tubes, LEDC, or optical cables) between detonators, and other components at the blast site (e.g. blasting machines) the possibility of improper set-up of the blasting arrangement is reduced. With traditional, “wired” blasting arrangements (wherein the wires can include e.g. electrical wires, shock tubes, LEDC, or optical cables), significant skill and care is required by a blasting operator to establish proper connections between the wires and the components of the blasting arrangement. In addition, significant care is required to ensure that the wires lead from the explosive charge (and associated detonator) to a blasting machine without disruption, snagging, damage or other interference that could prevent proper control and operation of the detonator via the attached blasting machine. Wireless blasting systems offer the hope of circumventing these problems.
Another advantage of wireless detonators relates to facilitation of automated establishment of the explosive charges and associated detonators at the blast site. This may include for example automated detonator loading in boreholes, and automated association of a corresponding detonator with each explosive charge. Automated establishment of an array of explosive charges and detonators at a blast site, for example by employing robotic systems, would provide dramatic improvements in blast site safety since blast operators would be able to set up the blasting array from entirely remote locations. However, such systems present formidable technological challenges, many of which remain unresolved. One obstacle to automation is the difficulty of robotic manipulation and handling of detonators at the blast site, particularly where the detonators require tieing-in or other forms of hook up to electrical wires, shock tubes or the like. Wireless detonators and corresponding wireless detonator systems may help to circumvent such difficulties, and are more amenable to application with automated mining operations. In addition, manual set up and tieing in of detonators via physical connections is very labour intensive, requiring significant time of blast operator time. In contrast, automated blasting systems are significantly less labour intensive, since much of the set procedure involves robotic systems rather than blast operator's time.
Progress has been made in the development wireless detonators, and wireless blasting systems that are suitable for use in mining operations, including detonators and systems that are amenable to automated set-up at the blast site. Nonetheless, existing wireless blasting systems still present significant safety concerns, and improvements are required if wireless systems are to become a viable alternative to traditional “wired” blasting systems.