Chapter 5: Types of Explosives

Learning Objectives

• Describe high explosives, their properties, and storage requirements.
• Explain the properties of water-gel explosives.
• Describe the properties of emulsions.
• Describe blasting agents, their properties, and storage requirements.
• Explain the role of priming in blasting and consequences of under-priming.
• Describe the relationship between low explosives and deflagration.
• Explain common misconceptions and limitations regarding propellants.

Overview

Explosives can be obtained in packages and in bulk and are classified as either high or low explosives.

High Explosives

A high explosive has a very high rate of reaction, high pressure development, and the presence of a shock wave upon detonation.

Dynamites (1.1D)

Dynamites are explosives that contain liquid nitrate esters. The most common nitrate ester used is "NG," which is a mixture of nitroglycerine and nitroglycol. NG has the ability to:

• Withstand freezing temperatures
• Mix with other ingredients to reduce its sensitivity
• Be packed into cartridges after mixing

Gelatinizing agents in dynamites promote water resistance. Antacids promote stability in storage.

Dynamites are detonator-sensitive, which means they can be initiated by detonators or detonating cord. Most dynamites develop a high velocity of detonation (VOD) that tends to create a greater shock wave.

Cautions When Handling Dynamites

Dynamites must be treated with caution due to the following:

• Skin contact with NG or inhalation of NG vapours may cause a "powder headache." Wearing non-permeable gloves (e.g., nitrile gloves) when handling dynamites can reduce the risk. Refer to the explosive's technical data sheet for more information on appropriate personal protective equipment to wear when handling the product.
• Exposure to moisture and temperatures in excess of 50°C (122°F) causes the composition of dynamites to break down.
• Accumulations of NG liquid (sweat) from the cartridges are very sensitive to accidental initiation.
• Most dynamites can be initiated easily and produce intense heat.
• When the temperature exceeds 200°C (392°F), dynamites can explode.

Packaging

Dynamites are usually available in cartridge form. A paper wrapper prevents contact with the NG and protects the dynamite from moisture and contaminants. Cartridges are designed to maintain rigidity while being loaded into drill holes and to compress readily when tamped. For seismic and underwater blasting, cartridges made of heavy paper or plastic tubing are used. These materials allow for greater water resistance and protection from the elements.

Stability

Dynamites are stable under normal conditions. They may explode when subjected to fire, supersonic shock, or high-energy projectile impact. The risk of explosion is higher when dynamites are confined or in large quantities.

Water-Gel Explosives (1.1D)

Water-gel (also known as slurry) explosives contain ammonium nitrate (AN), which acts as an oxidizer. The AN is mixed with fuels, metal particles, and sensitizers. (Water gels do not contain NG.) The resulting explosive can be initiated by a high-strength detonator or a booster.

Water gels have a jelly-like consistency, are high density (1.1-1.5), and can be loaded into wet holes. They come in bulk or in sausage-like packing stapled shut on both sides.

The explosive in water-gel products is suspended in a thickened medium (gel) to protect it from external water. Many water gels have lower strengths and VODs than dynamites. But water gels are more stable and are highly water resistant.

Stability

Water-gel explosives can be initiated by extreme levels of shock, friction, or mechanical impact. As with all explosives, water gels should be handled and stored with care and must be kept clear of flames and excessive heat.

Emulsions (1.1D and 1.5D)

An emulsion explosive is a dispersion of minute droplets of ammonium nitrate oxidizer salt solution suspended in oil. Emulsifying agents prevent the separation of solution and oil in an emulsion. A bulking medium, in the form of gas bubbles or micro balloons, is added for density control. The more air that is added, the more sensitive but less powerful the blend becomes. Emulsions may also contain solids, such as aluminum, to enhance power.

Emulsions have varying consistencies, ranging from pumpable liquid to stiff putty. However, a grease-like consistency is the norm. Emulsions are also very water resistant.

Emulsions can come in bulk or packaged form. They are available as either detonator-sensitive or non-detonator-sensitive.

Emulsions are much safer to handle than other high explosives such as dynamites. There is no possibility of getting NG headaches from touching or smelling emulsions.

At low temperatures, emulsions may lose sensitivity. Consult manufacturers' technical data sheets for use and priming recommendations.

Stability

Emulsions are stable under normal conditions. They may explode when subjected to fire, supersonic shock, or high-energy projectile impact. The explosion risk is higher when emulsions are confined or in large quantities. The oxidizer increases the burning rate of combustible materials.

Blasting Agents (1.5D)

A blasting agent is an explosive that is insensitive to a high-strength detonator. Blasting agents are composed of ammonium nitrate. They also contain various other sensitizing fuels that are generally not detonator-sensitive.

Blasting agents are relatively inexpensive. Due to their low sensitivity, they are stable and safe to store, transport, and use. Most are not water resistant. Exposure to moisture can result in poor rock breakage, misfires, or noxious fumes (oxides of nitrogen).

A high-energy primer is required to initiate blasting agents. Under-priming may result in excessive fumes, poor fragmentation, and misfires.

ANFO and WR

Ammonium nitrate and fuel oil (ANFO) and water-resistant ANFO (WR) are the most common blasting agents. They consist of a mixture of dry ammonium nitrate (AN) and fuel oil (FO) in a bulk weight ratio of 94% AN to 6% FO. Aluminum granules may be added to the mixture for extra energy. To mix ANFO, the written approval of the Chief Inspector of Explosives (Canada) is required. WR is used when there is a possibility of moisture, but it is not waterproof and should never be used in wet holes.

Blasting agents are either dry (free-running) or slurry products. Most dry types of ANFO mixtures have no water resistance, so a plastic liner (sock) may be required for wet holes. Dry products are generally supplied in bulk or packaged in bags with oil- and water-resistant liners. When free-pouring ANFO, follow the manufacturer's recommendations for the minimum diameter of the drill hole. These will vary between suppliers.

Stability

Blasting agents are insensitive but pose a mass explosion hazard when stored in large quantities. That's because the strong oxidizing effect of AN increases the burning rate of combustible materials. Shock, friction, fire (or other sources of ignition), and the strong oxidizer may cause fires or explosions.

Low Explosives

Most low explosives are solid, combustible materials that decompose rapidly but do not normally detonate. This action is known as deflagration. Deflagration is an explosive reaction such as a rapid combustion that moves through an explosive at a velocity less than the speed of sound.

Black Powder (1.5S)

Black powder is a low-explosive mixture of potassium nitrate, charcoal, and sulfur. It has no water resistance, is sensitive to heat sources and friction, and is highly flammable when dry. Upon initiation, it burns rapidly (deflagrates) with no shock wave. This produces a heaving rather than shattering action.

Black powder is used in fireworks, special-effect devices, and the (non-shattering) production of marble and slate. In finer grades, it is the core of safety fuse.

Propellants (1.4S2)

A propellant is a low-explosive mixture of a range of chemicals (e.g., nitrocellulose and ammonium nitrate) that varies between products and manufacturers. Propellants are sold in hard, water-resistant cartridges of various diameters and weights with igniters installed.

Propellants are used for breaking boulders (depending on their size), other rock, and concrete. Propellants may be effective for specialty uses (such as in sensitive marine environments). However, they can be costly and inefficient for blasting bedrock.

Important: There is a common misconception that propellants produce less ground vibration, air blast, and fly rock than high explosives in surface-blasting operations. But in fact, propellants produce almost the same values of ground vibration and air blast (based on scaled distance) and fly rock as high explosives. In addition, propellant cartridges have a limited range of diameters and weights that can't be altered. This limits the blaster's ability to make adjustments.

For information on storage requirements for propellants and other high-hazard special purpose explosives, see sections 255 to 265 of the federal Explosives Regulations.