This invention relates to a blasting arrangement.
A typical blasting system consists of a blast controller connected to a plurality of detonators by means of an appropriate harness. Once the detonators have been positioned inside boreholes prescribed procedures are carried out by an operator to ensure that the blasting system is fully functional.
Great care is taken when a blasting system is established. Nonetheless a malfunction can occur and, when this happens, it is vital to be able to render the blasting system safe i.e. to place the system in a condition in which the detonators cannot be initiated or fired. For example an operator who detects a potentially unsafe condition should be able to neutralize the blasting system particularly if the system has already been readied for firing. In this type of situation it is highly desirable for the operator to be given a clear signal that the blasting system has been put into a safe mode. The operator will then in confidence be able to approach the detonators and take suitable remedial action.
Many devices have been proposed for use in blasting systems and in other electrically-based arrangements wherein use is made of a fuse which provides a vital connection between a power source and detonators or other equipment. If an unsafe or unwanted condition is detected the fuse is open-circuited to render the arrangement safe and, at the same time, an indication is given of the conducting state of the fuse. The specifications of U.S. Pat. Nos. 5,936,508, 6,373,370, 6,456,189, 6,480,091, 6,809,627, 7,307,507 and 7,724,122 describe various kinds of fuses which provide a visual indication of a fuse-interrupted condition. This type of fuse is generally suited for use in a relatively confined situation in which the non-conducting status of the fuse is readily visually discernable. Also, the fuse is normally placed in a non-conductive state by virtue of a malfunction or unwanted condition arising in the equipment to which the fuse is connected. These characteristics mean that this type of indicating fuse is not well-suited for use in a blasting operation in which it is important, at least from a safety point of view, to have a substantial distance between an operator and a number of detonators and, despite the distance, for the operator being able to ascertain whether or not the blasting system is in a safe or unsafe mode. Additionally, as this type of indicating fuse is usually operable only in response to a malfunction or unwanted condition in the equipment to which the fuse is connected, it cannot normally be put into a non-conducting state by an operator.
Another approach to the requirement of providing a visual indication of an unsafe condition, in a blasting system, is described in the specification of PCT/ZA 2004/000130 wherein use is made of a link in a connection to a blasting system. The link is displaceable to a position at which the connection is automatically broken, thereby to render the blasting system safe, when an unsafe condition arises. The displacement of the link is done in a way which is visually apparent to an operator. Although in many respects the operation of this type of indicator, also referred to a mechanical flag, is satisfactory it has been found that, particularly in harsh environments, failures in operation can occur. The mechanical flag can be reset by an operator when required and although this feature does have some advantages it carries with it the inherent disadvantage that, through repeated use, the indicating system may become faulty.
U.S. Pat. No. 3,750,586 discloses a blasting arrangement which includes an energy source, at least one detonator, a blast controller, a circuit which establishes a connection between the energies force and the detonator and which, in response to a signal from a blast controller, allows energy from the energy source to initiate the detonator. The blasting arrangement further includes a device which in response to at least one actuating signal is operable to break the connection thereby preventing initiation of the detonator and to produce a discernible indication of its operation. This disclosure does not describe a way in which the device, upon operation, is rendered non-usable. This is desirable for safety reasons.
An object of the present invention is to provide a blasting arrangement which enables an operator, in a condition of relative safety, to establish the status of the blasting arrangement.