Basic explosives pdf

In the s, a large number of small dynamite bombs less than 20 lb were used in the United States. Moreover, this list also does not reflect the use of IEDs in active military theaters. Between the s and , a series of larger vehicle bombs emerged in terrorist attacks with main charges in the thousands of pounds range, but in the.

By the s, the use of HMEs in smaller charges was growing. Similarly, there was a related expansion from fertilizer-based materials to a more diverse range of possible precursor chemicals. HMEs are produced either by blending or cooking. Blending is the most common form of manufacture, and the simplest, as it requires only physically mixing the precursor chemicals together. To make a blended explosive, at least one precursor chemical must be an oxidizer a chemical source of oxygen and one must be a fuel a chemical or compound that can react with oxygen in a combustion-like process.

Cooking, a term borrowed from the narcotics enforcement community, is a more complicated manufacturing process to make HMEs wherein multiple precursor chemicals are mixed together and chemically react to form an explosive material. For many HMEs, more than one synthetic route is possible, involving different precursor chemicals. Groups involved in explosive attacks and the types of explosives employed by each are shown in Figure The remainder of the groups shown in Figure include bomb builders in the Iraq and Afghanistan conflicts as well as the newer factions encountered with the rise of ISIS and other extremists.

All of these groups use precursor chemicals to produce their HME charges. History has shown that the tactics developed by groups like Al-Qaeda in the Arabian Peninsula have migrated across the world.

For example, the trend of using concentrated hydrogen. The attempt to solve a problem by making policy in the midst of or in response to a crisis can create even greater difficulties. Perhaps one of the best historical examples of the pitfalls of narrowly focusing on immediate events, at least in the context of precursor chemicals, is that of the response of the United Kingdom to the explosives produced by PIRA during its bombing campaign. The PIRA bombing campaign began around and employed devices filled with readily available dynamite stolen from quarries and mines.

Responding narrowly to these events, both the United Kingdom and the United States increased controls on dynamite. In the United States, bombers migrated to readily accessible low-explosive fillers like black powder and smokeless powder which remain popular choices to this day. Such materials were not accessible in the United Kingdom, but PIRA was able to obtain farm chemicals to replace the dynamite. The first chemical PIRA used to produce HME mixtures and replace dynamite was sodium chlorate, a strong oxidizer used as a weed killer.

Sodium chlorate was mixed with the energetic fuel nitrobenzene to make small explosive charges. To counter the threat of chlorate explosives, the United Kingdom government mandated the addition of a diluent to weed killer to reduce its explosive potential. Many farmers in Northern Ireland possessed large quantities of AN as it was a chief fertilizer found in agriculture. In addition, with the heavy equipment required for farming, many of the same farmsteads were equipped with diesel tanks and pumps.

The net result was larger, fragment-producing bombs. These larger, heavier IEDs had to be delivered by vehicles due to their mass. CAN consisted of AN combined with dolomitic limestone a blend of calcium and magnesium carbonate. AN was soluble in water, and the dolomite diluent was not. By mixing the CAN in hot water the AN could be dissolved and separated from the insoluble carbonate component.

Once the solid was filtered out, the remaining liquid could be driven off to isolate nearly pure AN. The use of CAN in farming did not stop PIRA, but it did make the production of AN-based devices more time consuming and removed the least-adept bomb makers from the picture. Thus, the countermeasure had some limited effect. It was coarse and crystalline and would not absorb an optimum amount of diesel. To compensate for this change PIRA began using alternative fuels.

In , approximately 19 years after its introduction, PIRA discovered that crushing the CAN prills into a powdered form using either industrial strength coffee grinders or barley crushers eliminated the need to isolate purified AN. The pulverized CAN could be mixed with a variety of fuels to make an effective explosive filler.

Two fuels surfaced as constants: aluminum powder and powdered icing sugar. Aluminum was applied consistently for smaller, mortar-borne charges, and sugar was used in the larger-scale VBIEDs. Three of these bombs were deployed against the city of London, and one the city of Manchester. The largest was approximately 4, pounds roughly equivalent to the bomb used in Oklahoma City. Initially, groups attempt to procure commercial or military explosives if such are accessible.

In the absence of available explosives, they look for materials that can be blended. Denied the precursors for simple blends, they resort to processing materials to produce the feedstock of their explosives, such as by isolating AN from CAN.

With each level of difficulty introduced into the process, fewer bombers will be successful in their endeavors. However, any government creating controls for precursor chemicals must consider the tactics that will be developed in response. Precursor chemicals used to produce HMEs for IEDs can be categorized by type and role as oxidizers, fuels organic materials, energetic organic compounds, food products, or inorganic materials , and synthesis chemicals including strong and weak acids; Figure Not all precursor chemicals can be used to make the main charges for every bombing scenario.

These are not the only possible charges for each use-case. VBIEDs use charges ranging in mass from approximately 40 pounds to tens of thousands of pounds, depending on the carrying capacity of the vehicle.

Precursor chemicals used to produce these explosives tend to be fertilizers e. PBIEDs are typically encountered in backpacks, brief cases, small bags, and suicide bombing vests, belts, etc.

The charge mass of these devices is predicated on what the individual delivering the charge is capable of carrying. PBIEDs typically also employ a mass of fragmentation material, such as nails or screws, that can weigh as much as the explosive charge itself. We can break rock with a sledgehammer, and a detonation pressure is our explosive hammer. We can move rock with a bulldozer, and gas pressure is our explosive dozer. While the following discussion simplifies a complex and in some aspects largely theoretical subject, it should provide a basic grasp of blast mechanics.

The same mechanisms apply to whatever material is being blasted wood, concrete, steel, soil, ice, etc. As a result, this discussion will con- sider only monolithic bedrock in order to avoid confusion. Detonation Shock Wave Upon initiation, the detonation explosive oxidation zone proceeds down the column of explosive at the product's detonation velocity. The shock wave travels outward as a compression wave in all directions from the borehole, moving at or near detonation velocity.

The rock immediately surrounding the borehole is crushed to some extent, dependent on how much the force of the wave exceeds the compression strength of the rock. The force of the wave overcomes the elastic limits of the rock, causing it to bend outward and crack. If the rock mass is too large to permit bending, such as behind the borehole, no radial fracture occurs; the wave energy is simply absorbed by the rock. Shock Wave Reflection At this point, the result of the blast will only be very large wedge-shaped blocks, still interlocked.

However, when the shock wave reaches a free face, the outward-bending compressive force releases, and the wave is reflected back into the rock as a tension wave. The speed of the shock wave has been slowed somewhat, and its energy lowered, but if the distance from the borehole to the free face is not too great, it still carries enough force to overcome the tensile strength of the rock.

Rock, like concrete, has far greater strength in compression than in tension for instance, granite with a compression strength of 30, psi has a tensile strength of only psi. If there is no free face, such as behind the borehole, there will be no wave reflection and no lateral cracking. A point to remember is that any break in rock continuity will act as a free face; a crack or weather seam is as good as a quarry face in this regard.

Gas Pressure and Rock Movement Upon detonation, along with the shock wave, the solid explosive is instantly converted to superheated gas that is trying to occupy a space 10, to 20, times its original solid volume, and exerting a pressure that can exceed 1.

Without this gas pressure, the fractured rock would not move and would remain interlocked. The fractured rock mass has a certain inertia consider this a desire to stay where it is , which the gas pressure must initially overcome to start rock movement.

Once inertia is overcome, the rock moves outward away from the borehole at around one foot each 10 milliseconds, or between 40 and 70 mph, although smaller fragments can move faster and be shot out as flyrock. As with the detonation shock wave, nice even results in rock movement require rock continuity; cracks and weather seams will allow gas venting, and result in uneven and sometimes surpris- ing directions and distances of rock throw.

Figure The mechanics of blasting. It may be ex- pressed as a confined or unconfined value and is normally given in feet per second fps. The confined detonation velocity measures the speed at which the detonation wave travels through a column of explo- sive within a borehole or other confined space.

The unconfined velocity indicates this rate when the explosive is detonated in the open. Because explosives generally are used under some degree of confine- ment, the confined value is more significant. The confined detonation velocity of commercial explosives varies from to 25, fps Tables through With cartridge explosives, the confined velocity is seldom attained because complete confinement is usually impossible.

For blasting in hard rock, a high-velocity explosive is preferable. In a softer or highly jointed rock, a low-velocity explosive , for example, ANFO with a heaving action may give satisfactory results at a lower cost. Some explosives, and particularly blasting agents, are more sensitive to diameter changes than others. In charges with larger diameters, say six inches or more, the velocity may be medium to high.

These properties are: detonation velocity, density, detonation pressure, water resistance, and fume class. For a given explosive, these properties vary with the manufacturer. Specific gravity is the ratio of the density of the explosive to the density of water under standard conditions. The specific gravity of commercial explosives ranges from 0.

For free running explosives, the density is often specified as the pounds of explosives per foot of charge length in a given size borehole. With few exceptions, denser explosives give higher detonation velocities and pressures. Density is an important consideration when choosing an explosive.

For difficult blasting conditions or where fine fragmentation is required, a dense explosive is usually necessary. In easily fragmented rock or where fine fragmentation is not needed, a low-density explosive will often suffice. Low-density explosives are particularly useful in the production of riprap or other coarse products. The density of an explosive is also important when working under wet conditions.

An explosive with a specific gravity of less than 1. Figure Properties of a high-density ammonia dynamite. Table Properties of a low-density ammonia dynamite, low-velocity series.

Figure Properties of two-component explosives. The nomograph Figure can be used to approximate the detonation pressure of an explosive when the detonation velocity and specific gravity are known.

As can be seen, the detonation pressure is more dependent on detonation velocity than specific gravity. A high detonation pressure is necessary when blasting hard, dense rock. In softer rock, a lower pressure is sufficient. Sensitivity is the ease with which an explosive detonates.

In dry work, water resistance is of no consequence. In general, gelatins and emulsions offer the best water resistance.

Higher-density explosives have fair to excellent water resistance, whereas low-density explosives and blasting agents have little or none. Brown nitro- gen oxide fumes from a blast often mean the explosive has deteriorated from exposure to water. In addition, undesirable poisonous gases such as carbon monoxide and nitrogen oxides are usually formed. These gases are known as fumes, and the fume class of an explosive indicates the nature and quantity of the undesirable gases formed during detonation.

Better ratings are given to explosives producing smaller amounts of fumes. For open work, fumes are not usually an important factor, In confined spaces, however, the fume rating of an explosive is important. In any case, the blaster should ensure that everyone stays away from fumes generated in a shot. Carbon monoxide gradually destroys the brain and central nervous system, and nitrogen oxides immediately form nitric acid in the lungs.

Class A and Class 1 typically emit less noxious fumes per gram of explosive than Class B or Classes 2 or 3. For most explosives products, a shelf life of one year is recommended, although satisfactory performance can be expected from most products two, three, and even four years later. Consult the appropriate manufacturer to determine shelf life ratings be- yond one year.

NPS mandates a maximum shelf-storage of two years. When detonated or exploded, all explosives produce a flame that varies in volume, duration, and temperature. Black powder produces the longest lasting flame, while dynamites typically produce a shorter lasting, but more intense flame. Figure Properties of water gels. This is accomplished by adding certain salts to the explosives formula in order to cool or quench the flame to prevent the ignition of gas or dust within the confined space of a mine.

Permissible explosives are generally modified types of emulsions, water-gels, or ammonia dynamites, all in cartridge or chub form. Their reaction velocities are to less than feet per second. Black powder is a good example. These materials normally have little water resistance, are highly flammable, sensitive to a No.

Low explosives generally do not fragment rock as well as high explosives. Figure Nomagraph for finding detonation pressure. The reaction can be initiated by a No. Straight Dynamite - Nitroglycerin in an absorbent, with velocities between 10, and 20, feet per second.

This dynamite is the most sensitive of all commercial explosives. The weight strength is the actual percentage of nitroglycerin in the cartridge.

This explosive has poor fumes, good water resistance, and poor cohesion. There are three subclasses of ammonia dynamite: High Density: This product has a detonation velocity of to 13, feet per second, good water resistance, and fair to good fumes. Low Density: This product has detonation velocities between 7, and 11, feet per second, fair to good fumes and fair to poor water resistance.

Permissible Types: These products are similar to the low- density ammonia dynamites except that they contain cooling salts such as sodium chloride. Permissibles must be approved by the U. Bureau of Mines under specified conditions of usage. This material usually has good fumes and fair to poor water resistance. Gelatin Dynamite - Contains nitroglycerin gelled with nitrocellulose, and various absorbent filler mate- rials. Forms a soupy to rubber-like mixture which is water-resistant.

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