Explosives Used in Mining: an Overview
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-1800’s, 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 new discoveries in explosives and initiation technologies. A specialization principle, therefore, operates between military and civil application of explosives, thanks to new products economics, versatility, strength, precision or capability to be stored for long periods of time without significant deterioration.
Nevertheless, military-like shaped charges are sometimes used in the demolition of building and structures and ANFO’s characteristics (ANFO is an acronym for Ammonium Nitrate Fuel Oil mixture), though originally developed for use in mining, are also appreciated by the army.
Low Explosives vs. High Explosives
Explosives are chemicals, and as such, they bring reactions. Two different kinds of reactions (deflagration and detonation) allow distinguishing between the high and low explosives.
The so-called "low-order explosives" or "low explosives," such as Black Powder, tend to generate a large amount 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 use 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 special clay, called kieselguhr.
Primary vs. Secondary vs. Tertiary Explosives
Primary and secondary explosives are subcategories of high explosives. The criteria are about the source and stimulus strength that is necessary to initiate a given high explosives.
- Primary explosives can be easily detonated 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.
- Secondary explosives are also 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.
- Tertiary explosives, such as Ammonium Nitrate, need a substantial amount of energy to detonate, which is why they are, under certain conditions, officially classified as non-explosives. They are nonetheless potentially extremely hazardous products, as demonstrated by the devastating 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.