Mine blasting is no longer a simple activity, even when excavating large masses of solid rock. Maurice Jones reports
Safety and security has always been a major consideration during blasting but now requirements tend to be more sophisticated coupled with the usual demands for more efficient production and mine development.
Some of the factors that have come into play more in recent years are:
* Increased security concerns meaning that explosive materials have to be better protected or rendered ineffective until placed where required.
* A trend to bigger blasts, both underground and on the surface, require more efficient explosives transport, charging and top reliability in initiation systems, explosives resistance to water, etc.
* Complaints from neighbours and increased control by authorities have led to the need for better control (and monitoring) of blast-induced vibration, such as by more precise detonation delays.
The increased use of ANFO (ammonium nitrate-fuel oil) bulk explosives in recent years, and especially the later development of pumpable emulsions, has produced benefits in more efficient handle and increased security through less likelihood of loss of dangerous explosive materials.
A further development that is increasingly common in underground applications is the use of emulsion mixing and pumping systems that incorporates ‘chemical gassing’ technology that only sensitises the materials mix to initiation once it is in the hole.
Major suppliers such as Orica and Maxam all now offer such facilities, perhaps as only part of an overall supply and service contract including the hire of the necessary preparation equipment. The density and viscosity of the blasting materials can be adjusted by a computer control system built in to the equipment. The mix/pump/sensitising modules can be available on skid-mounted units and./or carried on trucks to serve various locations.
Normet offers a wide range of dedicated charging vehicles to work on underground faces ranging from the Charmac 605 series for face sections of up to 65m2 and 8.4m height to the Charmac 9910 BC ANX 1000 that carries two 500-litre bulk explosives vessels and a large working platform of 1-tonne capacity. The Normet units can handle ANFO and emulsion explosive and have been adapted to on-site sensitisation to compliance with regulatory requirements.
Orica’s detonation systems include remote initiation by the i-kon system. In this the detonators are not designated a delay before placing but are designated a delay by the electronic digital i-kon system. It can be used with the SURBS (Surface Remote Blasting System) for radio-signal for initiation, perhaps for several different blasts from up to 2500m away. Each system can accommodate up to 2400 i-kon detonators. This reduces blasting time to minimise pit closures and the suspension of other mining activities.
Video 1: Alpha Explosives, a Dyno Nobel agent in the western US, demonstrates open-pit hole charging using blast cord, detonators and bagged ANFO charges
Video 2: A safety training DVD produced by the Australian Centre for Geomechanics covering blasting in underground metalliferous mining