EOD Manual Volume 1 Chapter 1

What is an explosive?

"A substance which, when suitably initiated, undergoes a chemical change and exerts a sudden or intense pressure on its surroundings with a simultaneous evolution of heat and gases. Explosive materials may exist in solid, liquid, and gaseous states."

In the explosive industry what does the term 'explosives' refer to?

"A wide, inclusive term referring to energetic chemicals that when initiated produce light, heat, and gas (giving rise to pressure)."

What are the two conventional subcategories of explosives and what is the basis for this classification?

"High explosives and low explosives, subdivided according to their rates of decomposition — i.e., the speed at which the chemical state changes."

What are the 4 ways in which an explosive material can be initiated?

"Flash, friction, electrical current (or impulse), and impact."

What is oxidation in the context of explosives?

"A chemical reaction arising from an explosive material changing its state, or when fuel is burning. Oxidation is the process by which explosives produce energy."

Why is heat produced during an oxidation reaction?

Because the internal energies of the product (final) molecules are lower than the internal energy of the reactant (starting) molecules. The difference between these internal energies is the heat of reaction.

What is the 'heat of reaction'?

The difference between the internal energy of the reactant (starting) molecule and the internal energy of the product (final) molecule.

What is the 'heat of combustion'?

The heat of reaction in the case of burning fuel.

What is the 'heat of explosion'?

The heat of reaction in the case of high explosives.

How does the potential energy and energy release rate of explosives compare to petroleum fuels?

"Explosives usually have less potential energy than petroleum fuels, but their high rate of energy release produces great blast pressure."

What is the detonation velocity of TNT?

"6,940 m/s."

What is the detonation velocity of a pentane-air mixture?

"1,680 m/s."

What is the stoichiometric flame speed of gasoline combustion in air?

0.34 m/s.

How is the oxidation of low explosives described?

"As 'very fast burning'. When confined, the gases generated create a pushing effect caused by the expansion of the low explosive's volume to a volume larger than its original state."

What is detonation?

"An event where a wave propagates at a supersonic rate through a high explosive material. The propagation of the intense shock causes a radical change in the chemical and physical properties of the high explosive, leading to an oxidation process called detonation."

What is deflagration?

The oxidation of a high explosive material at a relatively slower velocity than the original oxidation velocity intended for that high explosive. The oxidation process in deflagration usually involves burning of the high explosive. The burn front propagates through the high explosive at a velocity slower than the speed of sound.

What is Deflagration-to-Detonation Transition (DDT)?

"A phenomenon that may occur during deflagration of a high explosive in confined environments. Gases from burning become trapped; as pressure increases, the reaction rate correspondingly increases because hot gases are forced into the unburnt explosive. The increasing pressure generates waves of increasing shock velocity. Given sufficient time and distance, these pressure waves reach shock velocity sufficient to cause detonation."

What causes the increasing reaction rate during DDT?

"Hot gases are forced into the high explosives that have yet to deflagrate, causing increasing pressure build-up that generates waves increasing in shock velocity."

When does DDT commonly occur?

"When bulk explosives are disposed of by burning, when fire occurs in bunkers storing high explosives, or when disposing of ordnance using special demolition techniques — where confinement may be provided by the ordnance casing opened by the demolition explosive."

What is sympathetic detonation and what can trigger it?

The initiation of a quantity of high explosives that then triggers the detonation of the rest of the high explosives nearby. DDT initiating a quantity of high explosives can trigger the rest through sympathetic detonation.

What happens when a high explosive detonates to produce blast overpressure?

"The explosive compound is rapidly converted into gaseous products. These hot gases expand immediately, compressing the surrounding air to form a shock wave. The outward movement of air causes damage along its path and sets up a compression wave in the surrounding medium. Successive layers of air are likewise compressed and expand until the wave gradually subsides through attenuation."

What is attenuation in the context of blast waves?

"The process by which a blast wave gradually subsides, with pressure decreasing corresponding to time and distance from the explosion."

What determines the strength and destructive power of a blast wave?

The net weight and type of explosive used. The blast normally lasts for a few microseconds.

How does a blast wave behave when it hits a building?

Some of its energy is absorbed and some is deflected. Blast waves normally travel in the direction least likely to be opposed.

What is the vacuum (negative) effect of an explosion?

"During the outward movement of the blast wave, a vacuum is created behind it where pressure is reduced to below atmospheric pressure. This is called the negative phase of an explosion. It lasts longer than the positive phase and can be equally as destructive. Window panels and objects of lighter weight will fall inwards against the direction of blast as a result of the suction."

What is the positive phase versus the negative phase of an explosion?

"The positive phase is the initial outward blast overpressure. The negative (suction) phase follows, where pressure drops below atmospheric; it lasts longer than the positive phase and can be equally destructive."

What is the channelling effect?

"When a shock wave impinges on a rigid target or surface, it undergoes deflection. Some energy is absorbed, and the remainder is deflected. The degree of deflection depends on the explosive nature, quantity, and distance. The movement of the wave in a specific direction influenced by the layout of the ground or buildings is known as the channelling effect."

What happens when a shock wave hits an object or surface?

"Some energy is exerted on the surface, some is deflected, and the remainder diffracts (bends) around it, engulfing the entire object from the side."

What is primary fragmentation and how is it maximised?

"Primary fragments comprise shrapnel from the container where the explosive is stored. To achieve maximum fragmentation, nails and ball bearings are added to the explosive — these are also regarded as primary fragmentation apart from that of the container."

What is secondary fragmentation?

Objects in close vicinity to the seat of the explosion that do not constitute part of the explosive ordnance or device. Secondary fragments form a major part of the collateral damage around the explosion site.

What are the thermal/incendiary effects of an explosion?

"High temperature at the point of explosion can reach up to 3,000–4,000 degrees Celsius depending on the amount and type of explosives. Victims close to the explosion can be charred or badly burnt. Hot fragments from the casing can also cause secondary fires if they land on flammable objects."

What are translation effects?

"The effect of objects being displaced, propelled, and distorted by either direct or indirect pressure waves. Objects and humans not shielded or in close proximity will be propelled at great velocity, and victims usually suffer fatalities and injuries due to acceleration and subsequent impact against a wall or ground."

What are secondary effects of an explosion?

"When an explosion occurs, blast and fragmentation may cause fire, rupture gas supply, electrical utilities, and water mains. These damages are termed secondary effects."

What is the shock front (shock zone) in a detonation?

A shock front that propagates at a characteristic velocity into the unreacted explosive at very high temperature and pressure. Immediately behind the shock front is the chemical reaction zone where the original material is rapidly converted into reaction products.

What is the chemical reaction zone in a detonation?

The zone immediately behind the shock front where the original explosive material is rapidly converted into reaction products. It is followed by a slower-moving zone consisting of the detonation products.

What determines the width of the shock front and reaction zone?

The nature of the explosive material and the boundary conditions.

Describe the pressure profile of a shock wave from explosion.

"Pressure rises from atmospheric to peak overpressure in a fraction of a microsecond (the positive phase), followed by a much slower decline (hundredths of a second) back to atmospheric, then continues to decline to sub-atmospheric pressure (the negative/suction phase) before returning to normal."

What is a high explosive?

A chemical material that detonates when initiated. Detonation is a decomposition reaction where the propagation velocity is greater than the speed of sound in the explosive material.

What are the 3 criteria for detonation?

(a) Reaction propagation velocity faster than bulk sound speed; (b) production of gas; and (c) production of heat.

Can high explosives detonate without atmospheric oxygen? Why is this significant?

"Yes. Detonation can occur in the absence of atmospheric oxygen, which allows high explosives to be used underwater."

What are inorganic explosives?

Explosives that do not have a carbon structure; most are fuels or oxidisers. Certain single-compound inorganic explosive materials are relevant as some form primary explosives (initiators).

What are fulminates and give an example?

Salts used as primary explosives. Mercury fulminate is the first inorganic explosive compound used as a primary explosive. It is a crystalline substance and is highly sensitive; it was used in early versions of blasting caps.

What are azides?

"Salts of hydrazoic acids. Important variants are lead azide, copper azide, silver azide, and sodium azide."

What is lead azide and what are its properties?

"An azide that is extremely sensitive to sparks, friction, and impact. It is perhaps the most commonly used material for detonators today. It has excellent storage characteristics, including being able to endure up to 260°C, and can be pressed quite easily if lubricated."

What is silver azide and its limitation?

Silver azide is able to withstand higher temperatures than lead azide but is sensitive to light unless contained in a light-proof container.

What is copper azide and how is it formed?

Copper azide is extremely sensitive and is usually a by-product when lead azide comes into contact with copper and moisture.

What is sodium azide used for?

Commonly used as a propellant to project vehicle airbags.

What is ammonium nitrate as an explosive and how can it be improved?

"Commercially produced in mass, ammonium nitrate is a poor quality explosive. It is over-oxidised and very difficult to initiate. It may become more effective when mixed with fuel oil to form ANFO, or in slurries."

What are the 4 factors used to gauge the quality of a high explosive?

(a) Velocity of Detonation (V of D); (b) Power; (c) Violence; (d) Figure of Insensitivity (F of I).

What is Velocity of Detonation (V of D)?

"The speed at which a shockwave travels through a detonating explosive substance, measured in metres per second. The shockwave is also known as a 'detonating wave'."

What does 'Power' refer to when gauging a high explosive?

The volume of gases produced from a given weight of explosive during an explosion. Power depends directly on this volume.

What does 'Violence' refer to when gauging a high explosive?

The ability of the explosive to shatter objects.

What is the Figure of Insensitivity (F of I)?

"A measure of the degree of force or friction required to detonate the explosive. The higher the F of I, the more difficult it is to initiate a detonation."

What is the shattering effect of high explosives?

"When high explosives detonate, they produce a shattering effect (like a pile driver driving against a boulder) due to the sudden and intense chemical reaction liberating gaseous products of explosion. The shattering effect is dependent on the velocity at which the shockwave travels."

What is the detonation rate of high explosives and what does this enable?

"High explosive shockwaves generally travel between 3,000 m/s to 9,000 m/s. This accounts for the sudden and intense effect that can shatter concrete and metal. When cast in certain shapes, high explosives can cut or punch holes through thick steel beams or armour plates."

How does confinement affect high explosives?

"High explosives are generally not limited or affected by confinement. The process of detonation continues at the velocity the high explosive is designed for. High explosive shockwaves may be exploited by casting them into certain shapes — e.g., encased in a metal case to create fragmentation like a fragmentation hand grenade."

What is the nature of a high explosive detonation in terms of control?

A high explosive detonation is generally uncontrollable and functions as designed when initiated.

What are the 3 subtypes/categories of high explosives?

"Primary explosives, secondary explosives, and tertiary explosives."

What are primary explosives?

"Extremely sensitive to mechanical shock, friction, and heat, to which they respond by burning rapidly or detonating. They are used as initiators."

What are secondary explosives (base explosives)?

"Relatively insensitive to shock, friction, and heat. They may burn when exposed to heat or flame in small, unconfined quantities, but detonation can occur. They are sometimes added in small amounts to blasting caps to boost their power. Examples: Dynamite, TNT, RDX, PETN, HMX. PETN is the benchmark — any compound more sensitive than PETN is classed as primary."

What are tertiary explosives?

"Generally insensitive to shock; they cannot be reliably detonated with practical quantities of primary explosive and instead require an intermediate explosive booster of secondary explosive. Examples include military main charges like TNT or plastic explosives, or in commercial use, blasting agents like ANFO and slurry (wet bag) explosives used primarily in large-scale mining and construction."

What is the purpose of boosters in tertiary explosives?

Boosters of secondary explosive are used to initiate tertiary explosives such as ANFO and slurry (wet bag) explosives.

What are the uses of high explosives?

"Initiators (disruptive initiators), intermediaries, and main charges."

What are disruptive initiators?

Generally include detonators. The high explosives used are less stable than main charges and are highly sensitive to shock and/or friction. They are used to initiate more stable high explosives. Detonators are often made from tetryl and fulminates.

What are intermediaries in the explosive train?

"Less sensitive high explosives like primers, used to develop the impulse from the detonation of disruptive initiators to a magnitude sufficient to cause detonation of the main charge. An example is detonating cord."

What is a main charge?

"Generally the main source of high explosive that creates the shattering effect or other required high explosive effect. Main charges are generally very stable and usually require a disruptive initiator to detonate. Examples: plastic explosives, TNT blocks, or high explosive filling in artillery rounds."

What is the explosive train (initiation sequence / firing train)?

"The sequence of charges that progresses from relatively low levels of energy to initiate the final explosive material or main charge. There are low and high explosive trains. A low-explosive train is as simple as a rifle cartridge (primer and propellant). A high-explosive train usually includes an igniferous initiator, a disruptive initiator (primary explosive), an intermediary (secondary explosive), and a main charge (tertiary explosive)."

What is a low explosive?

"Usually a mixture of a combustible substance and an oxidant that decomposes rapidly. An explosion is a rapid rate of burning that takes place on the surface of the substance and burns layer by layer through the explosive. The burning takes place in the absence of atmospheric oxygen, with the explosive having its own oxygen, meaning low explosives can burn underwater."

What are the 4 classifications of low explosives?

"Pyrotechnics, propellants, smoke-producing material, and igniferous initiators."

Can low explosives be detonated by a detonator?

No — low explosives cannot be detonated by a detonator.

What is the pushing effect of low explosives?

"Low explosives create a pushing effect when they explode, akin to a bulldozer pushing a boulder. Physical materials like metal may bend and concrete may crack when low explosives explode."

What is the rate of burning of low explosives and how does confinement affect it?

"Low explosives burn at a rate of up to 3,000 m/s. The rate of burning is proportional to the degree of confinement — the more confined, the more rapid the rate of burning, giving rise to an explosion. If left unconfined in the open, they generally burn off rapidly. For example, gunpowder left open on the floor burns off rapidly, while gunpowder in a bullet casing produces the necessary pushing power to project the bullet out of the barrel."

How can the rate of burning of low explosives be controlled?

"A 1 lb block burns slower than when broken into grains, because the collective surface area of the grains is greater than that of the block, exposing more area to the flame at any one time. By varying the degree of confinement, density of packing, and shape of the explosive, it is possible to control the rate of burning."

What is a pyrotechnic?

"A low explosive material that when burned will produce light, usable heat, smoke, gas, and sound."

What are propellant charges and give examples?

"Low explosive charges used for propulsion. Examples: propellant charges for small arms ammunition (SAA), propellant charges for mortars and artillery bag charges, and rocket propellant charges."

What are sound compositions and give examples?

"Pyrotechnic compositions that produce sound. Examples: thunder flashes, stun grenades, and small arms ammunition blanks."

What are smoke compositions and give examples?

Pyrotechnic compositions that produce smoke. Examples: smoke grenades in various colours.

What are incendiary compositions and give examples?

Pyrotechnic compositions that produce incendiary effects (fire/heat). Examples: thermite grenades or phosphorus ammunition like tracer small arms ammunition.

What are igniferous initiators (as low explosives)?

"Initiators used to initiate an explosive chain, like a safety fuse or a shock tube. They are generally safe to handle but are able to provide the friction or flash required to initiate a detonator."