Lesson 7.2: Explosives

Lesson 7.2: Explosives

We took a “bird's-eye view” of explosives and blasting in the last lesson. Now, we need to zoom in and look at many of these concepts in greater detail and with more rigor. First, a definition:

An explosive is an agent, compound, or mixture that undergoes very rapid decomposition when initiated by heat, impact, friction, or shock.

• This decomposition is a high-velocity, exothermic reaction, accompanied by the liberation of vast amounts of energy and hot gases at tremendously high pressure.
• High explosives produce shock, which fragments rock, and force, in the form of expanding gases, which displace and throw the rock.

The detonation velocity (DV) is the speed at which the detonation front propagates through a column of explosive.

• The explosive is said to detonate if the DV is supersonic, DV>3000fpm
• The explosive is said to deflagrate if the DV is subsonic, DV<3000fpm

In everyday conversation, some use the word detonate to mean either detonation or deflagration. From this point forward, we should be more precise in our use of the words.

The Three Common Components of Industrial Explosives:

Oxidizers

This group contributes oxygen, and includes nitrated salts such as ammonium, calcium, and sodium nitrate.

Fuels

Fuels produce heat, and include fuel oil, carbon, granular aluminum, TNT, black powder, and other carbonaceous material. Some of these materials are referred to as sensitizers, which increase the energy output, e.g., granular aluminum. We are not going to talk about the use of black powder because it is illegal for use in underground coal mines, and that was its only application to mining. TNT or dynamite is rarely used in mining applications due to the challenges of using it safely. Virtually all explosives used in the mining industry are based on ammonium nitrate and fuel oil (ANFO), and we will confine our discussion to those ANFO-based formulations.

Figure 7.1.1 Ammonium nitrate-fuel oil (ANFO) explosive

Image obtained from Wikimedia Commons licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Stabilizers

These impart properties to improve the handling of the explosive and include flame retardants, gelatins, densifiers, emulsifying agents, and thickeners.