Written by Steven Sayers
Gas pressure rock/concrete breaking products using pyrotechnic charges have been around for many years. These technologies replace previous high-explosive methods with a slow burn, ‘deflagrating’ low-explosive. Of course, many of the technologies that accomplish low impact blasting have been limited by their cost, among other drawbacks. Using a more benign tool, called the GasBlaster ™, environmental and safety concerns are alleviated, including a significant reduction in fly rock, noise, shock wave, vibration, dust levels, released nitrate gasses and damage to the surrounding environment—a revolution in hard rock narrow vein blasting.
How does it work?
In final production form, GasBlaster ™ is a sealed plastic tube with a solid high tech plastic core centrally connecting the fixed (blue) end stops. When the pyrotechnic charge (filled around the core) is ignited (via standard detonators), the initial deflagration pressure forces the two (red) high tech plastic collars up the face of the (blue) conical retaining end stops. This action locks (self stems) the charge in the drill hole (now drillable at any angle). Very quickly thereafter, the charge releases its full energy potential, breaking the core and bursting the sleeve to create the desired heaving effect to break rock.
The device can be used above ground for dimensional stone quarrying and to reduce large rocks post major blasting, rock removal in construction environments, hard rock mining and concrete demolition applications. Especially beneficial for marine applications, the technology also reduces shockwaves, which helps safeguard marine life.
Compared to Traditional Methods
Two key differentiators between deflagration (rapid heating) and detonating in relation to blasting include the speed of the reaction/process and the storage and logistics involved. The pyrotechnic process operates at around 100 meters per second, whereas high explosives are typically in the 7,000-8,000 meters per second range. Without containment, the pyrotechnic charge will not produce a large reaction of any kind and will just gently burn out, but high explosive charges would still detonate with potentially damaging consequences.
Although the gas pressure pyrotechnic blasting process has been around since the 1960's, the process has been used minimally compared to traditional high explosive blasting techniques due to a lack of reliability and a failure rate of about 30 percent underground. Not to mention, it's traditionally been a labour intensive process, making it less cost effective.
An even greater drawback in early gas pressure blasting methods was the process of "stemming,” or filling the drill hole (post charge insertion) with an inert and sufficiently heavy material to retain the charge in the drill hole until it achieves its maximum low-explosive heaving effect. Because it is a manual process, operatives must be highly skilled in material compositions used (usually locally sourced sand mixtures) and in the consistent packing of the drill hole to produce a good stemming effect—hence, the high failure rate.
A number of other products with varying degrees of sophistication have been available for non/low explosive blasting, but their drawbacks have not fully allowed industries to pursue low impact techniques. Cardox, for example, is considered an expensive option for a continuous/regular process, using a well-engineered steel cartridge system that requires re-fill products and retrieval and maintenance regimes. NoneXTM and PCF are other popular options, but require stemming to perform, which limits the angle of use and introduces a fairly high inherent failure rate underground. The mining and demolition industry need a mixture of each system that is cost-competitive (volume driven), stemm-free, reliable and less harmful on the environment.
DGP (Global) LLP believes its new patented technology answers those calls, and has already successfully field tested the product in South Africa under advanced international field trials at a prominent gold mine. Tooling for volumetric production is in the process of being finalised and various form factors are being investigated to establish the right mix of cartridge sizes, but it is expected to be out of the prototype stage soon and introduced into the global market during the course of 2012/2013.
GasBlast benefits over current methods:
Reduced fly rock
Negligible vibration and noise
Reduction in noxious nitrate fumes (no nitrates in pyrotechnic charge)
Coarse fragmentation in mined/demolished medium results in significantly reduced dust levels
Reduced logistical issues (transportation/storage 1.4S (UN0432) classification)
Unattractive medium for terrorists (harmless unless embedded in hard rock)
Improved health and safety (no unexpected explosions even if set alight)
Reduced down time (operatives can work in much closer proximity to blast face)
Higher productivity due to potential continuous mining
Reduced destruction of precious semi-precious stones/gems (bigger gem stones due to low impact heave as opposed to destructive shock waves produced by explosion)
Can be used in environmentally sensitive areas where explosion is not allowed/desirable such as built up areas/marine/nature reserves