Are civil and military explosives the same? In other words, are we using the same explosives in mining and warfare? Well, yes and no. From the ninth century AD (though the historians are still uncertain about the exact date of its invention) to the mid-1800s, black powder was the only explosive available. A single type of explosives was therefore used as a propellant for guns and for blasting purpose in any military, mining and civil engineering application.
The Industrial Revolution carried discoveries in explosives and initiation technologies. A specialization principle, therefore, operates between the military and civil application of explosives thanks to new products economics, versatility, strength, precision or capability to be stored for long periods without significant deterioration.
Nevertheless, military-like shaped charges are sometimes used in the demolition of building and structures and ANFOs characteristics (ANFO is an acronym for Ammonium Nitrate Fuel Oil mixture), though originally developed for use in mining, are also appreciated by the army.
The so-called "low-order explosives" or "low explosives," such as Black Powder, tend to generate a large number of gasses and burn at subsonic speeds. This reaction is called deflagration. Low explosives do not generate shock waves.
Propellant for gun bullet or rockets, fireworks, and special effects are the most common applications for low explosives. But even though high explosives are safer, low explosives are still in use today in some countries for mining applications, basically for cost reasons. In the US, Black Powder for civil use is outlawed since 1966.
On the other hand, the "high-order explosives" or "high explosives," such as Dynamite, tend to detonate which means they generate high-temperature and high-pressure gasses and a shock wave traveling at about or greater than the speed of sound, that break down the material.
Contrary to what most people think high explosives are often safe products (especially as far as secondary explosives are concerned, refer here below). Dynamite can be dropped, hit and even burned without accidentally exploding. Dynamite was invented by Alfred Nobel in 1866 precisely for that very purpose: allowing a safer use of the newly discovered (1846) and highly unstable nitroglycerine by mixing it with a special clay called kieselguhr.
Due to their extreme sensitivity to heat, friction, impact, static electricity. Mercury fulminate, lead azide or PETN (or penthrite, or more properly Penta Erythritol Tetra Nitrate) are good examples of primary explosives used in the mining industry. They can be found in blasting caps and detonators.
They are sensitive especially to heat but will tend to burn to detonation when present in relatively large quantities. It may sound like a paradox, but a truckload of dynamite will burn to detonation faster and easier compared to a single stick of dynamite.
Which is why they are, under certain conditions, officially classified as non-explosives. They are nonetheless potentially extremely hazardous products, as demonstrated by the devasting accidents involving Ammonium Nitrate in recent history. A fire detonated approximately 2,300 tons of ammonium nitrate caused the deadliest industrial accident in U.S. history that occurred on April 16, 1947, in Texas City, Texas. Close to 600 casualties were recorded, and 5,000 people were injured. Hazards link to ammonium nitrate have been more recently demonstrated by the AZF factory accident in Toulouse, France. An explosion occurred on September 21, 2001, in an Ammonium Nitrate warehouse killing 31 people and injuring 2,442, 34 of them seriously. Every window was shattered within a radius of three to four kilometers. Material damages were extensive, reported to be in excess of 2 billion Euros.
An increased global supply of minerals is essential to meet the needs and expectations of a rapidly rising world population. This implies extraction from greater depths. Autonomous mining systems, developed through sustained R&D by equipment suppliers, reduce miner exposure to hostile work environments and increase safety. This places increased focus on ground control and on rock mechanics to define the depth to which minerals may be extracted economically. Although significant efforts have been made since the end of World War II to apply mechanics to mine design, there have been both technological and organizational obstacles. Rock in situ is a more complex engineering material than is typically encountered in most other engineering disciplines. Mining engineering has relied heavily on empirical procedures in design for thousands of years. These are no longer adequate to address the challenges of the 21st century, as mines venture to increasingly greater depths. The development of the synthetic rock mass (SRM) in 2008 provides researchers with the ability to analyze the deformational behavior of rock masses that are anisotropic and discontinuousattributes that were described as the defining characteristics of in situ rock by Leopold Mller, the president and founder of the International Society for Rock Mechanics (ISRM), in 1966. Recent developments in the numerical modeling of large-scale mining operations (e.g., caving) using the SRM reveal unanticipated deformational behavior of the rock. The application of massive parallelization and cloud computational techniques offers major opportunities: for example, to assess uncertainties in numerical predictions; to establish the mechanics basis for the empirical rules now used in rock engineering and their validity for the prediction of rock mass behavior beyond current experience; and to use the discrete element method (DEM) in the optimization of deep mine design. For the first time, miningand rock engineeringwill have its own mechanics-based laboratory. This promises to be a major tool in future planning for effective mining at depth. The paper concludes with a discussion of an opportunity to demonstrate the application of DEM and SRM procedures as a laboratory, by back-analysis of mining methods used over the 80-year history of the Mount Lyell Copper Mine in Tasmania.
This paper was written shortly after this author had presented a video lecture titled Why rock mechanics and rock engineering? at the invitation of the ISRM. The lecture addressed the more general topic of the importance of rock engineering in the 21st century, and may be of interest as complementary to this article. The lecture (~ 45min) may be heard at https://www.isrm.net/gca/?id=1309.