Explosives have been used for blasting purposes in civil engineering, military, and mining applications dating back to the ninth century. Previously, black powder was the only explosive available, we’ve progressed a lot and discovered many alternatives during the Industrial Revolution. Here are some of the major moments throughout the history of explosives in mining:
- 1818 First use of black powder in construction of road tunnel in Pennsylvania.
- 1846 Italian chemist Ascanio Sobrero discovers nitroglycerine.
- 1863 Wilbrand invents Trinitrotoluene (TNT).
- 1864 Swedish chemist Alfred Nobel develops first detonating blasting cap, two years later he also invents dynamite by mixing kieselguhr with nitroglycerine.
- 1907 Consumption of black powder in U.S. more than 287 million pounds.
- 1914 Fifty-one mile Panama Canal opens, largest engineering project to date, using more than 67 million pounds of dynamite.
- 1924 Largest industrial blast to date in U.S. fired at California Blue Diamond quarry using 328,000 lbs. of dynamite
- 1956 First use of ANFO by U.S. Steel Corp.’s Oliver Mining Division.
- 1959 Thirty-nine dynamite plants operating in the United States.
- 1960’s Tunnel boring machines begin to seriously impact the use of explosives in large tunnel jobs.
- 1969 Emulsion explosives introduced.
- 1995 One dynamite plant still operating in the United States.
Explosives are chemicals which react to cause the desired result of an explosion. There are two different types of reactions: detonation and deflagration. These two types of reactions help distinguish between high and low explosives.
Low-order explosives, or low explosives, such as Black Powder and Flash Powder tend to generate a large amount of gasses and burn at subsonic speeds; a reaction known as deflagration. The reaction from low explosives don’t generate shock waves. Low explosives are most commonly used for:
- Gun ammunition
- Special effects
- Mining applications in certain countries
Black Powder was outlawed for civil use within the United States in 1966.
High explosives can be broken down into three subcategories: primary, secondary, and tertiary.
- Primary explosives are the most volatile of the three subcategories, they can be detonated easily due to their sensitivity to friction, impact, statical electricity, and heat.
- Secondary explosives can also be sensitive, but less so than primary explosives. Secondary explosives are primarily sensitive to heat.
- Tertiary explosives need a substantial amount of energy to detonate. This has lead to them being officially classed as non-explosives in certain conditions. However, they are still extremely hazardous and can lead to devastating accidents (ie: Ammonium Nitrate caused the deadliest industrial accident in U.S. history).
High explosives commonly used in mining include:
- Primary: Mercury fulminate, DDNP, Tetrazene, Lead azide, PETN (penthrite, Penta Erythritol Tetra Nitrate). They can be found in blasting caps and detonators.
- Secondary: Dynamite, Water gels, Emulsions, TNT
- Tertiary: Ammonium Nitrate, ANFO (ammonium nitrate/fuel oil), Slurry (wet bag)
It may come as a surprise to some, but high explosives are actually quite a bit safer than you’d expect. This is especially true for secondary and tertiary explosives. A secondary explosive such as dynamite can be dropped, hit, and even burned without an accidental explosion occurring. This is the reason that the mining industry has moved from low to high explosives over the years, the higher cost of them is worth the added safety they provide. While some tertiary explosives such as ANFO are so insensitive to shock that they aren’t even reliably detonated by practical quantities of primary explosives.
The safety and cheap cost of Ammonium Nitrate has lead to it being one of the leading used explosives in mining, quite the change from the previously used, highly explosive black powder. Do you think the explosives used will continue to change, or we will find an explosive with no dangers outside of their intended use within a mine?