Chapter 12: Explosives Products

Explosives are the energetic materials used to blast rock. For best results, explosives should be selected by the properties and performance characteristics required by the blast design. A single product property does not indicate the suitability of that explosive for any given blasting application. All properties must be considered. This chapter discusses generic types of commercial explosives using properties and performance characteristics discussed in chapter 11. Explosive manufacturers offer technical guidance for product applications. Consult the International Society of Explosives Engineers (ISEE) Explosives Product Guide™ in your reference to manufacturers' products in these categories. A discussion of explosives properties and performance characteristics continues in chapter 11. Explosive products are categorized as either high or low explosives and distinguished primarily from one another based on the availability of oxygen for the detonation reaction (See chapter 11). Explosives products and general classifications are discussed in this chapter and are summarized in the ISEE Explosives Product Guide™ (See figure 12.1).

AMMONIUM NITRATE

Ammonium nitrate (AN) is a common ingredient in most commercial explosives and blasting agents. It is used in either a hot concentrated liquid solution or solid form. Pure AN is a white odorless salt, NH₄NO₃, that exists in five stable solid crystalline forms or phases. Each form is stable within a certain temperature range. As AN temperature cycles from one form's range to another, crystals go through a volume change. Solid AN is very soluble in water and is very hygroscopic (Keleti, 1985). Hygroscopic means solid AN readily absorbs and retains moisture. Absorption occurs under a combination of humidity and temperature conditions. Water has a degrading effect on solid AN and will cause caking and physical breakdown.

Ammonium nitrate is used in solution as an ingredient in emulsion explosives and in solid form to make explosives. Ammonium nitrate's predominant use is in the form of a small porous pellet (prill) used to make ANFO.

Ammonium Nitrate Manufacturing

Ammonium nitrate manufacturing is done in a continuous, rather than a batch process facility (See figure 12.2). The process reacts nitric acid with ammonia to create a hot liquid AN solution. At this stage the product is used either as a solution or is converted into small solid spherical pellets called prills for use as a fertilizer or an ingredient in other explosives.

Manufacturer's Specifications Various manufacturers produce ammonium nitrate products for use in the blasting industry. Their physical properties and performance characteristics may vary. The reader is encouraged to consult their local manufacturer or supplier for current product specifications, transportation, storage, and use requirements.

The AN prill production process is also a continuous process. It begins with spraying the hot concentrated AN solution (concentration 94% to 96%) through perforated plates or shower heads (See figure 12.3) at the top of a prilling tower. Liquid AN droplets are formed as the solution exits the shower heads (See figure 12.3) and pours to the bottom. During the free fall of 30.5 meters to 61 meters (100 feet to 200 feet), the droplets crystallize into spherical AN prills. These prills are dried, cooled, and may be coated with anti-setting agents prior to shipment. The major uses of AN prills are for agricultural fertilizers and explosives.

Some manufacturers use chemical additives to increase the phase temperature range. By increasing this range the transition temperature is raised reducing the possibility of cycling. Prill manufacturers minimize prill caking by coating them to retard the prill's affinity for moisture on its surface. Common coatings are liquid surfactants and finely ground calcium (from 125 micrograms) and materials like kaolin or talc. In some cases, the use of the surfactant alone has proven to be an effective coating. Due to their inert nature excessive amounts of talc or kaolin will decrease ANFO sensitivity. They may also interfere with oil absorption and distribution, which affects ANFO performance. Excessive amounts of certain surfactants may affect the stability of the emulsion in blending emulsion. This could in turn affect the performance of blends (ANFO/emulsion mixtures). A good blasting prill has typically less than 1.0 percent anti-setting coating.

Typically standard prills range from 1 millimeter to 2 millimeters in diameter. Some prills are manufactured to contain microballoons, which increases their internal void space and gives them a lower prill density. Blending with fuel oil is done on a weight basis.

Caution Bulk truck calibration should be maintained to ensure the correct 94:6 AN to fuel ratio by weight.

Due to the hygroscopic nature of ammonium nitrate, inventories should be kept at the minimum required for the operation and rotated when used in climate conditions that promote cycling.

Void Space

All prills contain void spaces both on the surface and internally (See figure 12.5). The blasting prill must contain a minimum level of void space within the prill. The voids in the blasting prill serve two important purposes: (1) they promote physical product uniformity and uniformity of fuel oil absorption and (2) they provide for product sensitivity by acting as sites for high-temperature "hot spots" or ignition points to enhance the detonation reaction.

Porosity is a measure of the amount of available void space at the surface of the prill to absorb and retain the fuel oil required for the product being made. Fuel oil absorption must be uniform. Prills best suited for blasting products have a particle (individual prill) density in the range of 1.3 grams/centimeter³ to 1.5 grams/centimeter³. AN prills with particle densities approaching the density of solid ammonium nitrate (slightly greater than 1.7 grams/centimeter³) are less sensitive to detonation.

Caution A prill's sensitivity increases as its internal void space increases.

Prill void space should not be confused with the space between prills when they're loaded into a borehole. This interstitial space is uniform and fixed for uniformly sized and shaped prills if all are perfect spheres, regardless of prill size.

Caution AN prill bulk density increases as prill size and shape becomes more mixed (e.g. nonuniform sized prills or prills with fines).

Mechanical Strength

Blasting prills must possess adequate mechanical strength to resist the breakdown that occurs with handling. Manufacturers have different methods of measuring and reporting prill strength. Handling should be limited to minimize mechanical breakdown and creation of fines, which causes nonuniform fuel oil absorption when mixing ANFO or blends. Fines also increase ANFO sensitivity. In bulk operations, prills are often delivered by means of pneumatic tankers and must be blown into storage in elevated silos. Air pressures should be kept at the minimum to allow the prills to flow but not break. Typically, prills should not be transferred with air pressures in excess of 62 kilopascals (9 pounds/inch²).

Caution Typically prills should not be transferred with air pressures in excess of 62 kilopascals (9 pounds/inch²). Consult your manufacturer for recommendations.

ANFO

ANFO and ANFO products have become the most widely used blasting materials since their introduction in the 1950s. Their dominant use is attributed to economy and convenience. ANFO's two major limitations are that it has (1) no water resistance and (2) a low bulk density. These should be accepted as potential product limitations before use. ANFO is a mixture of ammonium nitrate prills and fuel oil. These are mixed in the weight ratio of 94:6 as shown in figure 12.6.

The amount of fuel oil affects four important performance characteristics: (1) energy, (2) velocity of detonation (VOD), (3) sensitivity, and (4) fumes produced. ANFO is sometimes modified to create other ANFO products having other energy, and density characteristics. This is done in two ways by either (1) adding substances such as finely-sized aluminum or carbonaceous materials in conjunction with No. 2 diesel fuel, (2) or emulsifying the ANFO and packaging the product in a water resistant package for use in damp to slightly wet boreholes. At times other materials are added to add energy, water resistance, or sensitivity.

Energy

ANFO provides more energy per pound than any other explosive. ANFO is completely converted to gases on water, leaving no solid residues. ANFO's maximum theoretical energy (Q), work energy (E_aw), and VOD occur when ingredients are mixed in the proper weight ratio. The relationship between E_aw, VOD, and fuel oil content is illustrated in figure 12.7. A lower percentage of oil reduces the E_aw at a much faster rate than slight excess. On the other hand, ANFO is most sensitive on the low side of the range of 2% to 6% No. 2 diesel fuel oil (FO) and rapidly decreases in sensitivity above and below this range. Thermodynamic computer programs are used to calculate theoretical energy.

Caution Different manufacturers may report different "E_aw" values for ANFO.

As fuel oil content exceeds 6% the detonation process will produce carbon monoxide (CO), and as FO content falls short of 6% oxides of nitrogen (commonly called NOₓ) will be produced.

Physical Properties

Bulk density and water resistance are important physical properties of ANFO that affect loading and performance. The bulk density of ANFO depends on the density and size of the AN prill used in the mixture. Most ANFO has a bulk density ranging between 0.77 grams/centimeter³ to 0.95 grams/centimeter³ (48 pounds/foot³ to 56 pounds/foot³).

Caution ANFO bulk density values can vary from manufacturer to manufacturer. The reader should verify bulk density values from their manufacturer.

Pneumatic loading as described in chapter 21 and mechanical packing by augering equipment in a manufacturing plant increases the density of the finished ANFO product by fragmenting the prills and compacting the product. The maximum practical density of ANFO mixtures is about 1.10 grams/centimeter³. Many attempts have been made to increase the poured density and VOD of ANFO by grinding the prills to small particle sizes. Theoretically, as particle size decreases, the product density and detonation velocity increase. Practical field experience has shown that the increase in density and VOD achieved by grinding the prills increases the cap-sensitiveness of AN/FO products.

Water readily dissolves ammonium nitrate prills and desensitizes ANFO. The desensitizing effect of water has been evident in many poor blasts where ANFO was used in wet boreholes without sufficient external protection or blended with emulsion. Field experience has shown continuing good results can be obtained only when unprotected ANFO is used in dry boreholes.

Performance Characteristics

Performance characteristics (VOD, Q, and E_aw) directly influence blast performance. ANFO sensitivity is important to blasting results and product performance. The reader is encouraged to contact the manufacturer for these values as they can vary.

Sensitivity

The sensitivity of ANFO rapidly decreases as density increases above 1.20 grams/centimeter³ and is directly affected by the product void space volume as previously discussed.

Velocity of Detonation

The VOD of poured or bulk loaded ANFO depends on both the borehole diameter and degree of borehole confinement. Figure 12.8 illustrates how the detonation velocity of ANFO varies with borehole diameter assuming maximum confinement. The velocity curve illustrates that ANFO reaches a VOD of approximately 4,750 meters/second (15,600 feet/second) in a 310 millimeter (12¼ inch) diameter borehole. Optimum ANFO VOD is plotted against borehole diameter in figure 12.8.

The degree of confinement surrounding the ANFO materially affects the VOD and the product's ability to sustain a detonation in small diameter charges. For example, most ANFO will not detonate unconfined in diameters less than 100 millimeters (4 inches). However, when confined in a competent rock borehole, ANFO detonates in diameters as small as 25 millimeters (1 inch) or less.

Fumes

Properly manufactured ANFO, correctly applied, yields fumes rated Fume Class 1, as described by the Institute of Makers of Explosives in their Safety Library Publication (SLP) No. 12. This rating signifies very good fume characteristics. However, improper preparation or application of ANFO can produce undesirable quantities of toxic fumes, NO₂ and CO. Fume generation is discussed in chapter 28.

In blasts where ANFO produces large volumes of reddish or orange-brown clouds, toxic levels of NO₂ may be present. Table 12.1 lists factors that may create these fumes (See figure 12.9).

Table 12.1 – Factors contributing to ANFO fume production.

The idealized ANFO fumes vs. fuel oil content are shown in figure 12.9. Investigation of fume problems is complicated, despite the fact that theoretically, excess fuel oil content should lead to production of carbon monoxide (CO). In reality the reduced sensitivity of such mixtures may instead result in the liberation of oxides of nitrogen (NOₓ) if deflagration occurs.

Reactivity With Sulfides

The weathered products of pyrites (metal sulfides) can cause ANFO decomposition. Spontaneous decomposition and heating of ANFO in contact with these products, notably ferrous sulfate, has been observed in underground copper mines and reported by the U.S. Bureau of Mines at temperatures as low as 79°C (174°F) (Miron, 1992). Self-sustaining reactions of weathered pyrites and ANFO were observed at much lower temperatures at a large surface coal mine. Such reactions can produce sulfuric acid hard to melt boomers and the plastic covering on detonating cord, and can lead to premature detonation of the entire borehole explosive charge.

Inclusion of a small percentage of inhibitors within the ANFO can be beneficial when used to blast weathered pyrites. These inhibitors are known to slow down the decomposition of ammonium nitrate and have shown to be effective in preventing spontaneous decomposition.

Priming Requirements

When blasting with ANFO, as with any otherdunconfinedfactor, the manufacturer's priming recommendations should always be followed.

ANFO Products

The free-flowing nature of ANFO is well-suited for bulk loading applications. Bulk ANFO stored in bins is transported directly to the blast site in trucks designed to load the product directly down or into the boreholes. Bulk ANFO is usually mixed on the blast site as it is being loaded. ANFO products are also commercially available in bagged or packaged forms for conventional loading operations. Bagged ANFO is used only in dry blasting applications, while cylindrical cartridges are made for loading in wet borehole conditions. Water resistant ANFO (WR ANFO) discussed in this chapter can be used in boreholes where moisture degradation is a concern.

Manufacturer's Specifications Various manufacturers produce ANFO products for use in the blasting industry. Their physical and performance characteristics vary according to their intended use. The reader is encouraged to consult their local manufacturer or supplier for available product specifications, transportation, storage, and use requirements.

Bagged ANFO

ANFO is commonly mixed and packaged in 22.7 kilogram (50 pound) multi-wall paper bags, while outside the U.S. plastic bags are common. Bagged ANFO (See figure 12.10) is commonly used in the conventional borehole loading operations (See chapter 19). It is also commonly loaded into the pneumatic loaders discussed in chapter 21.

Cylindrical Cartridges

Cylindrical cartridges of ANFO (See figure 12.11) are made for conventional loading operations in wet boreholes. Product water resistance depends entirely on the integrity of the package. This can improve there is no direct capability of mixing or the package in the water. Thus, the cylindrical cartridges are available with water resistant HD ANFO (High Density) or HD ANFO is a blend of crushed and AN prills mixed with fuel oil. The cylinder packages are textile or cardboard tubes with tough plastic liners. This product is used in wet boreholes over 150 millimeters (6 inches) in diameter.

Crushing the prills produces packaged densities in the area of 1.05 grams/centimeter³. This density ensures the cartridge will sink in clear water in the borehole. Cartridged products may include dewatering agents and energy additives in their formulation. Densifying agents can be used to further increase the packaged density to 1.3 grams/centimeters³, allowing the product to sink more readily in borehole filled with water containing mud or drill cuttings. Energy additives such as aluminum granules can increase the cartridge energy and overcome the lower powder factors resulting from not completely filling the cross-sectional area of the borehole.

Crushing the prills also increases the product sensitivity. This improves its ability to sustain a detonation. This is helpful because the annular space between the cartridge and the borehole walls results in a lower degree of confinement than is obtained with poured or bulk products.

WR ANFO

WR ANFO is most commonly used in 65 millimeter to 127 millimeter (2½ to 5 inch) boreholes in wet blasting conditions for quarries, trenching, general construction and road cuts. It is designed for usage in wet or dripping boreholes that are too decoupled and should not be used in boreholes with severe water conditions. In addition WR ANFO at Fume Class I and can be used in underground environments. This product can also be used with pneumatic ANFO loaders in both surface and underground blasting applications, but it will require special precautions due to product tendency to product stickup in the horeholes.

WR ANFO is standard ANFO with a specialty coating applied to the prills. This coating is designed to create a moisture barrier on the prills and prevent water degradation so it can be used in light or medium wet conditions. These conditions can be described as borehole walls with dripping water or residual water from dewatering operations. When properly used, WR ANFO allows the energy factor of the blast design to be maintained.

Table 12.2 – Benefits of using WR ANFO.

WR ANFO has a density similar to ANFO. Therefore, the basic use benefits and limitations of ANFO apply. For example, when water is unexpectedly encountered in a pattern drilled in damp to moist usage WR ANFO allows the energy factor of the blast design to be maintained.

Manufacturing and Composition

An understanding of the water resistant coating additive is helpful for the blaster to determine its proper application. The additive's ingredients combine to form a quick-acting thickened coating to impart water resistance. The water resistant coating additive can include materials with benefits as listed in table 12.3.

Table 12.3 – WR ANFO coating additive ingredients.

The water resistant coating is applied to the ammonium nitrate prills immediately after oiling in an auger. In the auger the coating is thoroughly mixed to produce a uniform coating. It should be noted that the water resistant additives does not individually "waterproof" each ammonium nitrate prill. Rather, when WR ANFO is exposed to water the additives at the surface of the prills quickly thickens and forms a slurry-like barrier, which acts to reduce further water penetration into the explosive column. This mechanism results in a gel-like layer around the borehole wall and maintains a dry mixture column of ANFO. During the detonation reaction the dry ANFO core detonates and the heat of reaction aids the explosive characteristics of the gel layer, so that all detonation products are consumed completely.

Field Use Considerations

WR ANFO is free flowing and slightly less sensitive than ANFO and should be primed in accordance with the manufacturer's recommendations. The product should always be in "dry contact" with the primer, or the top cartridge of explosive added after the primer. Water flowing through the borehole can wash out a part of the explosive column. WR ANFO is more susceptible to wash out than are cartridged explosives. Multiple priming techniques are recommended if this potential exists.

WR ANFO is designed to work in light and medium water conditions. "Light" water conditions are considered to be wet and dripping boreholes, with no substantial accumulation of water at the borehole bottom. In these situations, the borehole is primed and WR ANFO is loaded directly in the same way as ANFO. The additive on the ANFO surface will "wick" the water to the walls of the borehole and prevent it from wicking farther into the explosive column, which could result in ANFO desensitization. If there is a small amount of water at the bottom of the borehole, the primer can be held several inches off the bottom when the borehole is loaded with WR ANFO so that the primer and product are in dry contact.

WR ANFO should never be poured directly through water. This loading practice causes the product to lodge in the borehole or allow pockets of water to form in the explosive column. Boreholes with more than a few inches of water in the bottom require dewatering and/or a cartridge product loaded to build a level above points where water is entering the borehole.

Once there is a dry explosive cartridge above the water level, WR ANFO is immediately loaded onto boreholes in the same manner as regular ANFO. Simply slit the bag and pour. This product produces full borehole coupling and provides protection for the explosive column from additional water incursion.

WR ANFO should be loaded and detonated in the same day.

Caution At no time should WR ANFO sleep longer than 24 hours.

WR ANFO can also be manufactured on and loaded by an ANFO auger truck. The ANFO auger truck is modified with an additive feeder (See chapter 20) to add the coating agent in to the loading auger after the fuel oil injection point. Bulk WR ANFO is well suited to large-scale projects with light water conditions where the heave and fragmentation of ANFO products is desired. It is best to consult with an equipment manufacturer and a water resistant additive manufacturer when considering bulk usage.

DYNAMITE

Dynamite is a cartridged explosive used only in conventional (non-bulk) loading applications. The first dynamite resulted when Alfred Nobel discovered that relatively large quantities of nitroglycerin (NG) could be absorbed into kieselguhr and made safer to transport and use. Kieselguhr, also known as diatomite, is a natural deposit of the siliceous shells of diatoms. When ground to a fine state it acts as an absorbent. A British patent was issued to Nobel for his dynamite in 1869. Since then, dynamite has performed admirably and has served as the mainstay of the commercial explosives industry until recent times.

Kieselguhr absorbs up to three times its own weight of nitroglycerin and provides a safe and convenient method for transporting and using nitroglycerin.

Nobel realized that the kieselguhr not only did not contribute to the energy of the explosive, but actually absorbed heat and subtracted from it. Eventually, therefore, he replaced the kieselguhr with active ingredients, such as sodium nitrate, an oxidizing agent, and wood pulp, an absorbent, carbonaceous combustible. In these dynamites, energy was derived not only from the nitroglycerin, but also in part from the reactions of the sodium nitrate with the combustibles.

Composition

Modern dynamite products are defined as detonator sensitive mixtures that contain nitroglycerin as a sensitizer or as the principal means for developing energy, and when properly initiated, dynamite decomposes at a stable detonation velocity. Today where field conditions permit, low-cost blasting materials have replaced dynamite. Water gels and emulsions have been developed to replace dynamite where performance requirements and conditions do not favor the use of ANFO products.

Today's dynamite differs from Nobel's original mixture. It is composed primarily of a mixture of liquid nitrate esters, a gelling agent, oxidizing salts, fuels, and materials called dopes. Dynamite is classed as a sensitized explosive (See chapter 11). The mixture of liquid nitrate esters includes nitroglycerin and nitroglycerol. Nitroglycerol has a lower freezing temperature than nitroglycerin and when used yields better product cold weather properties.

Nitrocellulose is the gelling or thickening agent that gives dynamite water resistance and prevents fluid leakage from the cartridges. Fuels provide energy and the oxygen supplied by the oxidizers support the detonation. Ammonium nitrate and sodium nitrate are the main oxidizing salts most commonly used. Dopes provide a variety of useful properties. Over the years various formulas of nitroglycerin and the other diverse materials have been modified to produce different types and grades of dynamite.

Energy

Energy can vary among dynamite grades, but in general they tend to be high brisance energy explosives. The blaster should consult the manufacturer's technical information sheets for specific energy values.

Physical Properties

Dynamite is a cartridged explosive mixture wrapped in paper shells or plastic film/tubes. It is more rigid than cartridged emulsion or water gel products. Dynamite products are compacted by tamping as boreholes for increased loading density and borehole coupling. Dynamite physical properties vary considerably by grade. Specific properties should be considered for the desired application. The most important dynamite properties to consider are density and water resistance.

Performance Characteristics

Dynamite performance characteristics also vary considerably. In the past, dynamite grades often carried descriptive names such as ditching dynamite and lump coal that suggested their primary application. Four important performance characteristics to consider based on the criteria are: (1) energy, (2) VOD, (3) sensitivity, and (4) fume class. Since characteristics vary, manufacturer's technical information sheets should be consulted for specific product grade information.

Dynamite selection for a specific application also requires consideration of a number of rock and workplace factors (See table 12.4). Each blast presents some variety of these conditions, and thus a dynamite grade with the proper combination of properties, and with the proper packaging, should be chosen.

Table 12.4 – Dynamite grade selection criteria.

Packaging

Dynamites are packed in cylindrical cartridges (See figures 12.12), 19 millimeter (¾ inch) diameter and larger, with lengths ranging from 100 millimeters to 610 millimeters (4 inches to 24 inches). Various paper shells or wrappers are used to package dynamite and protect it from moisture. The weight (as in relation to the weight of the dynamite contained inside), coating, and type of wrapper have an important influence on the dynamite's fume production, water resistance, tamability, and loadability. Dynamites are packaged to meet the oxygen balance and loading characteristics necessary for field use.

Dynamite Product Types

The four basic types of dynamite are: (1) granular, (2) semigelatin, (3) gelatin, and (4) permissible. The basic distinction is that gelatin and semigelatin dynamites contain nitrocellulose, a cellulose ester that combines with nitroglycerin to form a cohesive gel. The viscosity of this product depends on the percent of nitrocellulose. Granular dynamites, on the other hand, contain little or no nitrocellulose and have a grainy texture.

Manufacturer's Specifications Various manufacturers produce dynamite products for use in the blasting industry. Their physical properties and performance characteristics vary according to their intended use. The reader is encouraged to consult their local manufacturer or supplier for available product specifications, transportation, storage, and use requirements.

In addition to this classification, dynamites differ also in the materials used to provide their principal source of energy. In "straight" dynamites, nitroglycerin is the principal energy source, augmented by the reaction of various active absorbents called "dopes". Most notable among these are sodium nitrate and carbonaceous combustibles. In "ammonia" dynamites, frequently referred to as "extra" dynamites, ammonium nitrate replaces a large portion of the nitroglycerin to give a less expensive and more impact-resistant product. In "ammonia" dynamites the ammonium nitrate is the principal source of energy and nitroglycerin serves primarily as a sensitizer. The term "ammonia" is not scientifically correct, but it is the term used in the explosives industry since its beginning.

Granular Dynamites

Granular dynamites contain little or no nitrocellulose and have a grainy texture. Two types of granular dynamites (1) straight and (2) ammonia-granular are discussed here.

Straight Dynamites

In "straight" dynamites the percentage of nitroglycerin defines the grade. For example, dynamite with 50 percent nitroglycerin was called "50 percent straight dynamite."

These "straight" dynamite grades had roughly the same energy as black powder, but their performance was much superior to black powder because they consistently detonated at higher velocities. After the introduction of ammonia dynamites, the relatively high cost, sensitivity to shock and friction, noxious fumes, and very high flammability limited the use of "straight" granular for general blasting. Ditching dynamite, a 50 percent "straight" dynamite, is designed for ditch blasting by the propagation method and is the only grade which has survived any present usage for general blasting.

Ammonia-Granular Dynamites

Ammonia-granular dynamites, also known as "extra" dynamites, are dynamites in which the primary source of energy is derived from the reaction of ammonium and sodium nitrate with various fuels. Nitroglycerin contributes to the explosive energy, but is primarily a sensitizer that ensures complete reaction of the nitrate/fuels mixture. Consequently, in these dynamites the ammonium nitrate, with an explosive energy of about 70 percent that of nitroglycerin, replaces nitroglycerin as a primary energy source.

Compared to straight-granular dynamites, ammonia-granular dynamites are generally lower in velocity and energy, less water resistant, less sensitive to shock and friction, less flammable, and considerably more economical. The safety and economic advantages of these ammonia dynamites far outweigh any performance sacrifice to straight dynamites.

Semigelatin Dynamites

Semigelatin dynamites are ammonia dynamites that contain a small amount of nitrocellulose as a gelling agent. There are no straight semigelatin dynamites. Usually, semigelatin dynamites have higher percentages of nitroglycerin than "extra" granular dynamites. With nitrocellulose and nitroglycerin combined to form a gel, these products have better water resistance and a more cohesive, semigelatin texture than granular dynamites.

Also, semigelatins generally have a slightly higher velocity than granular dynamites with equal strength markings. A semigelatin series can be varied in velocity, density, and water resistance characteristics.

Because of its good water resistance, low fume-generation characteristics, and cohesive consistency, semigelatins are popular in underground mining and quarry blasting.

A semigelatin ammonia dynamite 22 millimeters × 610 millimeters (⅞ inches × 24 inches) is frequently used in presplitting and other controlled blasting techniques. Cartridges often have a hollow, friction-fit sleeve, which slides over other cartridges to form a column of explosives. It is normally detonated by a 10.5 gram/meter (50 grain/foot) detonating cord, half hitched around every third or fourth cartridge.

Gelatin Dynamites

The two types of gelatin dynamites are (1) straight-gelatin and (2) ammonia-gelatin. In general, gelatin dynamites use nitrocellulose rather than absorbent dopes to hold the nitroglycerin and to maintain product consistency. Thus, they have a higher nitroglycerin and nitrocellulose content than semigelatins and satisfy the need for a more gelatinous, greater water resistant, higher velocity dynamite. The product consistency varies from a soft to a tough, rubbery gel, depending on the percent nitrocellulose content.

Straight-Gelatin Dynamites

Straight gelatins were introduced a few years after the straight granular dynamites. The original form was the "blasting gelatin" (91% nitroglycerin, 8% nitrocellulose, and 1% chalk), which was expensive and had an excessively high velocity for blasting rock. It was soon replaced by a series of straight gelatins with graduated strengths comparable to the straight dynamites in the granular series. Ammonia gelatin replaced straight gelatin for the same reasons ammonia-granular dynamites replaced straight-granular dynamites-safety and economy.

This series contains nitroglycerin and nitrocellulose as the only explosive ingredients and sodium nitrate with other dopes. Straight-gelatin dynamites, which correspond to straight-granular dynamites, vary in strength from 20% to 90%. These dense, plastic, cohesive and highly water-resistant explosive are used for blasting very hard, tough rock.

Consistent sensitivity, high velocity, and performance of gelatins depend upon entrapped air in the gel. This entrapped air develops during the manufacturing mixing process. If the entrapped air is lost under pressure or during long storage, the velocity of the gelatin dynamite may be reduced and gaps vary over a rather wide range. "Hi-velocity" gelatins were developed, which retained their high velocity under pressure and after long storage periods by entrapping air in small microballoons dispersed throughout the mixture. Examples of this type of dynamite are seismic gels, developed especially for shooting under the high pressures found in deep-hole seismograph work.

Ammonia-Gelatin Dynamites (Extra Gelatins)

These dynamites differ from straight gelatin in that a portion of the strength is derived from ammonium nitrate. These products enjoy great popularity because of their high density, high velocity, and good water resistance.

Permissible Dynamites

Permissible dynamites are those that have been approved by the Mine Safety and Health Administration (MSHA) for use in underground coal mines. They must be stored and used in accordance with conditions established by MSHA.

All explosives when detonated give a flame that varies in volume, duration, and temperature. Permissible dynamites are ammonia dynamites, either granular or gelatin types, that have a flame-depressant additive, such as sodium chloride, which reduces the volume, duration, and temperature of the explosive's flame. They are designed to minimize the probability of a gas or dust ignition in underground coal mines under conditions or other applications, which must comply with permissible regulations.

Permissible explosives, particularly the low-velocity grades, absorb moisture readily and deteriorate as a result. For this reason, storage and rotation of stock must be carefully supervised. In general, good conditions of storage should be provided. Stock purchases should be consistent with needs, and the oldest stocks should be used first in order to minimize chance of storage. Once permissibles are taken underground, they should be used as soon as possible, as specified in the MSHA permissibility regulations.

Permissible dynamites are made in both granular (comparable to the ammonia or extra dynamites) and gelatinous varieties. The granular dynamites are used to blast coal, while the gelatinous varieties are generally used for rock work.

Storage

Dynamite must be handled and stored in accordance with all Federal, state, and local regulations. Stock levels should be consistent with the rate of use, and the oldest stock should be used first. Dynamite showing signs of deterioration should be destroyed in an approved manner by an experienced person. The manufacturer or distributor of the explosive should be consulted for assistance prior to the destruction or disposal of any deteriorated explosive.

EMULSION

Emulsion explosives had their beginning in 1961 when Richard Egly and Albert Neckar of Commercial Solvents Corporation filed a U.S. patent application for a blasting agent composed of a blend of a water-in-oil emulsion and a solid oxidizing agent such as ammonium nitrate. The patent was granted in 1964.

Egly and Neckar were trying to make a waterproof ANFO rather than a new type of emulsion explosive. Subsequent developments in the 1960s and early 1970s resulted in emulsion explosives with various dynamite grade minimum diameter and detonation velocity characteristics. Eventually emulsions were developed with characteristics that allowed their safe and efficient use in high-volume bulk loading systems as discussed in chapters 20 and 22. Emulsions result in a very intimate fuel and oxidizer mixture with performance characteristics close to those of ideal explosives.

Emulsions are intimate mixtures of two immiscible liquids called phases with one phase uniformly dispersed throughout the second phase. Mixture separation is prevented with active ingredients called emulsifiers. Thus, emulsion explosives are dispersions of water oxidizer solutions in a fuel oil medium ("water-in-oil" emulsions). The fuel oil and AN droplets as shown in figure 12.13 are the two phases.

The oil or fuel phase is known as the continuous or external phase because it surrounds and coats all of the oxidizer droplets. The fuel phase is generally No. 2 diesel fuel (FO) and/or mineral oil or a combination of the two. However, other fuels can be used.

The water or oxidizer solution phase is called the discontinuous or internal phase because the microscopically fine droplets are kept apart and surrounded by the continuous fuel phase. The water phase always contains ammonium nitrate. Other salts such as sodium nitrate, calcium nitrate and ammonium or sodium perchlorate may also be included.

The oxidizer salts, regardless of temperature, will not easily crystallize and grow because there are so many small oxidizer droplets. Since the oxidizer salts remain in solution, the detonation properties of emulsion explosives remain unchanged for long periods of time and over wide temperature ranges giving emulsions excellent shelf life characteristics. This high ratio of oxidizer to fuel and the intimacy of the mixture give emulsion explosives their excellent performance characteristics.

The oxidizer remains dispersed in the fuel to form a stable emulsion through the action and effectiveness of its emulsifier (surfactant). The emulsifying agent reduces the interfacial surface tension between the phases and prevents phase separation. For example, oil and vinegar are held together by egg yolks to form the emulsion known as mayonnaise. There are many different emulsifiers, and choosing which one to use depends on the particular requirements for the product. The emulsion formed from the fuel phase, oxidizer phase and emulsifier, before any addition of bulking agent, aluminum, or solid ammonium nitrate, is called the matrix and is the foundation for subsequent products.

The three emulsion ingredients are mixed in the approximate weight ratio illustrated in figure 12.14.

Manufacturing

Emulsion manufacture may be done in a continuous or batch process either at fixed plants or mobile equipment. A hot oxidizer salt solution is combined with oil and an emulsifying agent and reworked to high shearing rates (emulsified). These oxidizer solutions are prepared at elevated temperatures to minimize the product water content. These oxidizer solutions are normally held at temperatures between 50°C to 90°C (122°F to 194°F) depending on the quantity and type of oxidizer salts used.

Increasing shear energy through mixing reduces the oxidizer droplet size. Reducing droplet size for a given composition improves product stability and increases viscosity. Increased viscosity occurs because of the increased droplet surface area and the resulting decrease in FO volume (continuous oil phase) layer between droplets.

Emulsions can be viewed as either oxygen balanced or fuel rich mixtures. Fuel rich emulsions are generally less viscous and easier to pump than oxygen balanced emulsions. When formulated properly, fuel rich emulsions may be blended with dry AN prills the emulsion contains enough extra fuel to oxygen balance blends.

To achieve more over-oxygen balance the volume of oxidizer must be much greater than the volume of fuel (the ratio is approximately 9:1).

Because the relative volume of fuel is so much less than that of the oxidizer, it must be spread in a very thin layer in order to cover all of the oxidizer droplets. The size of the droplets is very small and, due to the oxidizer fuel ratio, the droplets are in the shape of polyhedrons. Droplets are usually in the range of 0.2-10 microns in diameter, or about 1/40th to 1/2000th the size of a grain of table salt.

Energy

The addition of aluminum or ANFO to an emulsion explosive can be used to increase its energy (calories/gram). Theoretically, an addition of 5% aluminum will increase the energy of the emulsion by about 25% to 35%. Ten percent (10%) aluminum increases fuel energy by about 45 to 60%. Above 10% the addition of aluminum may not be cost effective.

ANFO added to emulsions can increase that energy by about 3% for every 10% incremental added. ANFO also has the added advantage of producing only gaseous detonation products, and therefore, an increase in gas volume is also realized. An increase in gas volume usually leads to better heave and throw of the rock being blasted. The ratio of the amount of energy released to the calculated thermochemical energy is the measure of the efficiency of an explosive.

Aluminum does not significantly increase an emulsion's sensitivity. Therefore, a much coarser and less costly aluminum can be used to increase energy. Finer aluminum particles are required for small diameter products.

Physical Properties

Density, rheology, and water resistance best define the physical properties of emulsions.

Manufacturer's Specifications Various manufacturers produce emulsion products for use in the blasting industry. Their physical properties and performance characteristics vary according to their intended use. The reader is encouraged to consult their local manufacturer or supplier for available product specifications, transportation, storage, and use requirements.

Density

Since emulsions product densities can vary widely, the blaster-in-charge is advised to consult the manufacturer for specific product density information.

Chemical gassing creates gas bubbles in the emulsion that not only lower density but increase sensitivity. The volume expanding effects due to gassing that cause its density to decrease are illustrated in figure 12.15, where a field cup density check is being conducted.

The bulk loading density of standard bulk emulsions and those with microballoons is constant throughout the borehole, whereas the loading density of chemically gassed emulsions varies as illustrated in figure 12.16.

Rheology

The rheology (viscosity) of the emulsion is controlled by the nature of the fuel phase and the oxidizer droplet size. The fuel phase composition (wax, oil, emulsifier) has the greatest influence on the final rheology of the product (See figure 12.17). The final viscosity and stability of an emulsion depend on the four factors: (1) volume ratio of the oxidizer solution to oil, (2) type of oil used, (3) type and quantity of emulsifying agent used, and (4) purity of ingredients.

The droplet size is controlled by the amount of work (shear) put into the emulsion. The faster and longer it is stirred (sheared), the smaller the droplet size and better the distribution. Smaller droplet sizes make more viscous (thicker) emulsions.

Low refinement best suits bulk products while high refinement best suits packaged ones. Rheology is adjusted for packaged and bulk products. Watery and high viscosity oils are used to make thick, putty-like packaged products (See figure 12.18) to give them their firm structure for ease of handling and loading. Low viscosity oils, such as No. 2 diesel fuel, can be used to make them more fluid for pumping applications.

Commercial explosive companies have developed various compositions, which provide similar but still uniquely different properties to an emulsion. Most modern emulsion blend compositions will have a shelf life of several months to over a year.

Water Resistance

Emulsions are extremely water resistant due to their continuous oil phase. In packaged form they do not depend upon the integrity of the package for water resistance. Emulsions are a good choice when loading wet boreholes because they will perform successfully after sleeping underwater for weeks or even months.

Performance Characteristics

Emulsions fail to exhibit impact and friction tests, which have been standard in the explosive industry for years. When placed against a metal plate, the emulsions fail to detonate under the impact of a 150 gram, 30 caliber projectile. Other high velocity impact tests with larger caliber projectiles show emulsions to have a greater resistance to initiation by impact than either water gels or dynamite as illustrated in figure 12.19. Normally emulsion explosives will not detonate during burning, but there is an awareness of this, particularly if the material in exposed to foreign materials such as rust, detonators, dynamites or aluminum powders. When pumping emulsions, care must be taken so that the pump does not run dry or against a closed system ("deadhead"). In either case, friction can raise the temperature of the emulsion in the pump beyond the decomposition point of ammonium nitrate or other ingredients. If this happens, a detonation can occur.

Caution! It can be just as hazardous to pump unemulsified emulsion oxidizers as it is to pump sensitized ones.

Although tests have demonstrated that emulsions offer a great degree of safety, they will detonate if subjected to severe conditions. They are explosives, and regardless of their inherent degree of safety, emulsion explosives should never be abused.

Velocity Of Detonation

It is an established fact that the velocity of detonation (VOD) increases as the explosive's ingredient particle size gets smaller. Since the droplet size of emulsions is so fine, the VOD of emulsion explosives is very high and close to theoretical. The VOD does decrease somewhat as the charge diameter decreases or as solids such as aluminum or AN prills are added, but the VOD generally remains relatively high when compared to most water gels as illustrated in figure 12.20.

Sensitivity

An emulsion's sensitivity can vary for a number of reasons. Generally, an emulsion's sensitivity increases as its density decreases. It's also true that sensitivity increase is an emulsion's water content decreases. The water content and density of blasting agents is usually higher than that of 1.1D emulsions. This keeps the overall bulk strength energy level of blasting agents close to that of the high explosive emulsions. Because emulsions have a very fine particle size and are an extremely intimate mixture of fuel and oxidizer, only a density reducing agent needs to be added to make them detonable. It is not necessary to use high explosives or chemical sensitizers for sensitivity. The density can be reduced by occluded air, chemically generated gas, perlite, expanded plastic, hollow glass or plastic microballoons (See figure 12.21) or even AN prills.

The initiation sensitivity of emulsions can be made to vary from that of a U.S. classified No. 8 strength detonator (before containing 420 milligrams to 450 milligrams of PETN) for a high explosive 1.1D classification at 79°C (65°F) to booster sensitivity for blasting agent, 1.5D products. The emulsions are sensitive over a wide temperature range, and they also maintain their sensitivity over a wide range of diameters 22 millimeters (>⅞ inches) and up for "Explosive, Blasting, type E 1.1D" (high explosive) and 38 millimeters (1.5 inches) and up for "Explosive, Blasting type E 1.5D" (blasting agent). Different density reducing agents are used for various reasons, but glass or plastic microballoons are the most common, although chemical gassing is becoming popular. Because certain glass microballoons well withstand high pressures, they are especially useful in sensitizing emulsion products for use in deep boreholes or close borehole spacing where high hydrostatic or shock pressures are likely to be encountered.

Detonation Pressure

Because emulsions have a high velocity of detonation and reasonable density, they also have a relatively high detonation pressure. Emulsion detonation pressures measured by the "aquarium" technique are found to be between 100 kilobars and 120 kilobars (1.45 × 10⁶ pounds/inch² to 1.74 × 10⁶ pounds/inch²). As a result, emulsions are particularly well-suited for improving fragmentation in hard massive rock, for breaking hard bottom rock, and for use as a booster for ANFO mixtures and other blasting agents.

Emulsion Products

Determining which emulsion explosive to use for a particular application depends on all of the explosives properties as well as those of the rock formation to be blasted. Consult the manufacturer's product information sheets and consult with your supplier to determine the best products for your application.

Emulsion products are provided in bulk form as sensitized blasting agents and as unsensitized (matrix) for blending with ANFO. Matrix products are classified as oxidizer for transportation.

WATER GEL/SLURRY

Because water gel explosives contain substantial amounts of water and separate oxidizer and fuel components, they are intrinsically less sensitive than the traditional water-free, nitroglycerin (NG) dynamite explosives. The original water gel explosives were sensitized with the explosive trinitrotoluene (TNT) and/or smokeless powder. Even so, they were not cap sensitive and were classified as Propellant Explosive, Class B, the forerunner of the current Blasting Agent (1.5 D) classification.

The late 1960s saw the development of detonator sensitive, smaller diameter water gel explosives, Class A (1.1 D) type explosives. Water gel products were subjected to the standard impact, shock and burning test. They were generally shown to be significantly less sensitive than the NG dynamites. The test results were not interpreted to imply that water gels could not be accidentally detonated, but that they are less sensitive to accidental stimuli. Nor do they indicate that comparable results will always be obtained in the field. Typical sensitivity tests are described below.

Water gels generally have a liquid and a solid phase. The two phase components are not as intimately associated as they are with emulsions. This is due to the fact that a relatively large amount of oxidizer surrounds a relatively small amount of fuel. The continuous liquid phase of the water gel is usually thickened by guar gum or other long chain organic polymers. These thickeners are then cross-linked which means the polymer molecules are joined by a chemical bond to form the final gelled product. These thickeners and cross-linkers combine to impart the various types of final gel structure required for specific applications.

Water gel explosives consist of oxidizing salts and possibly fuels dissolved or dispersed in a continuous liquid phase. The entire system is thickened and made water-resistant by the addition of gelling and cross-linking agents. The oxidizing salts are usually selected from ammonium nitrite (AN), sodium nitrate (SN) and calcium nitrate (CN). Aluminum, coal, gilsonite, sugar, ethylene glycol and oil are frequently employed as fuels. Water gels are generally made at elevated temperatures and as the product cools, oxidizer salt crystals begin to form (See figure 12.22). The tendency for crystals to form increases as it cools even during storage.

Manufacturing

Water gels are manufactured in both packaged and bulk form. If a product is intended for use as a high volume bulk product, the water gel can be formulated on-site with solids, gellants and a cross-linker added as the product is pumped into the borehole. Before loading stemming materials, sufficient time, as prescribed by the manufacturer, must elapse for the gelling action to occur. If it is under at a distant site with all ingredients except a cross-linker it will remain sufficiently fluid to be easily pumped yet sufficiently viscous to maintain a stable dispersion of the solids in the continuous aqueous phase. When, as the product is pumped into the borehole, a cross-linking chemical and/or extra gum or a pumpable suspension is added, the product gels to a demonstrably stable water resistant explosive. An added advantage of this type of product is that it completely fills the borehole.

Water gels may be sensitized with a variety of ingredients. Typical sensitizers include chemical and physical means either alone or in combination, where: (1) chemical sensitizers include the nitrate salts of organic amines, nitrate esters of alcohols, perchlorate salts, fine particle size aluminums, or other explosives; and (2) physical sensitizers include entrapped air or chemically-produced bubbles, or microballoons (glass or plastic composition).

Energy

Water gels have energy ranging between 700 calories (gram and 1,500 calories/gram). As is true with all explosive formulations, whether or not this energy is completely developed and utilized is dependent on how effectively the explosive is formulated, primed, confined, and protected from influences such as water or other adverse conditions prior to, or at the time of detonation.

Physical Properties

Density

Water gel densities generally range from about 0.80 grams/centimeter³ to 1.60 grams/centimeter³. Most are formulated in the range of 1.00 grams/centimeter³ to 1.35 grams/centimeter³. For specific products, however, water gels have been produced and used at densities as low as about 0.4 grams/centimeter³. Because water gels range widely in suitable diameter boreholes and slump to larger diameter holes, water gels can be loaded with higher loading densities than the more rigid and denser dynamites. For example, a 25 millimeter (1.25 inch) diameter water gel at a density of 1.1 grams/centimeter³ using loads in a 45 millimeter (1.75 inch) borehole at a borehole density of about 0.89 kilograms/meter (0.60 pounds/foot).

The loading density of packaged water gels is limited by the package stiffness and its coupling ratio (See chapter 14). Loading density can be increased by tamping, by slitting or in vertical boreholes.

Rheology

Water gels are made with three different rheologies for: (1) packaged (See figure 12.23), (2) pourable, and (3) bulk products. The consistency of a packaged water gel is shown in figure 12.23. The pourable water gels are only partially gelled in their package to provide a flowing rheology (See figure 12.24). Bulk water gels are gelled with a cross-linker as the product is pumped into the borehole. Full gelling action takes place within the borehole. Each is well suited for its specific use.

Water Resistance

Water gel water resistance is generally very good. However, like dynamites it can be significantly decreased if the products are not used in the proper and recommended manner.

Performance Characteristics

Water gel products are available with the wide range of performance characteristics. Manufacturers should be consulted for specific physical properties and performance characteristic information.

Velocity of Detonation

Most water gel velocities of detonation increase as their diameter and degree of confinement increases. In actual field use, the detonation velocity of the water gel may be greater or less than the published velocity depending on diameter and confinement.

Sensitivity

Water gels are reliable relative to conventional priming methods. They are significantly more resistant than dynamite to accidental initiation from abusive impact, shock, or fire. Water gels are formulated to be detonator sensitive for some applications and detonator insensitive for other applications. Even the most sensitive grades have made many standard sensitivity tests obsolete because they fail to detonate at the upper limits of these tests. Consequently, new tests have been developed and implemented to evaluate the relative safety of these products. If crystals form within the water gel its sensitivity can be affected. As crystals increase in number and size, product sensitivity decreases and its detonation efficiency decreases.

Product temperature does not remain constant after loading. Product temperature will equilibrate with the borehole temperature in time. While freezing may not reduce the effectiveness or safety advantages of water gels, cold product must be allowed to reach its minimum recommended temperature before detonation. Ambient ground temperatures in the continental United States are 4.4°C (40°F) in higher, with a temperature of 13°C (55°F) close to the average found in most areas.

Priming recommendations for individual water gel grades at various temperatures are detailed in the Product Information Bulletins available from the manufacturer.

Water Gel/Slurry Products

Water gel/slurry products are available in two basic forms, packaged or bulk. Packaged products are made in cartridges and shot bags as shown in figures 12.25 and 12.26. Water gels offer a wide range of compositional variations. Thus the physical properties and performance characteristics may be varied over a broad range, making it possible to accommodate a wide variety of blasting requirements.

Manufacturer's Specifications Various manufacturers produce water gel products for use in the blasting industry. Their physical properties and performance characteristics vary according to their intended use. The reader is encouraged to consult their local manufacturer or supplier for available product specifications, transportation, storage, and use requirements.

BLENDS

Blends are mixtures of either (1) a water-based explosive material matrix and ammonium nitrate or ANFO or (2) a water-based oxidizer matrix and ammonium nitrate or ANFO (See figure 12.27). (IME SLP 12). Typically blends are not detonator sensitive and are usually classified by the U.S. Department of Transportation as "Blasting Agents" with a UN classification of 1.5D Explosives, Blasting, Type E, No.0332. This chapter discusses blends mainly used in bulk loading of large diameter boreholes greater than 150 millimeters (6 inches) of the 1.5D classification. Nevertheless, many of the concepts described will apply to all explosive blends.

The ratio of matrix to ANFO spans the range from 1% emulsion to 99% emulsion. Most blends fall in the emulsion to ANFO ratio range (20:80 to 50:50). For blends containing less than 50% emulsion, the explosive mixtures are sometimes called "Heavy" ANFO. In some cases emulsion is mixed with straight AN prills rather than ANFO, provided the emulsion contains enough fuel to properly oxygen balance the final blend. The three main benefits of blends are to (1) increase the density of ANFO to increase energy in the borehole to enhance fragmentation, (2) provide water resistance to ANFO, and (3) reduce overall project cost by permitting expanded drill pattern.

Manufacturing

Blends are mixed either at fixed plants or in mobile bulk trucks. Fixed sites produce blends for packaged products or they pre-blend for bulk products. Sometimes bulk blending trucks are used to pre-blend for other shot service truck deliveries. The most common method of making blends is in mobile bulk trucks on the blast site and directly loading into boreholes.

Fixed Site Blending

Blend formulations with a full spectrum of emulsion and ANFO ratios can be prepared at fixed plants which produce packaged blends in cartons or bags. These bagged products are then shipped, stored and loaded by the blast crew as required.

If blasting or distribution sites are large enough, blends can be prepared by using fixed emulsion and AN storage tanks at the explosives storage area to mix directly into non-blending auger and pump trucks. This type of operation produces blends with predetermined fixed emulsion/ANFO ratios. These operations are called "preblend" operations.

Mobile Bulk Truck Blending

It is relatively easy to mix the emulsion with the AN prills or ANFO to form a blend and several techniques have been developed for this purpose. One of the more common types of equipment is a blend truck (See chapter 20). Sometimes the truck will also have a bin to add aluminum to make higher energy blends. When mixed on a blending truck, the system calibration is very important to maintain product quality and consistency. The blend truck manufacturer should be consulted for proper calibration procedures.

A calibrated amount of AN is continuously fed by a bottom auger from the AN bin into a mixing auger. At the same time, a calibrated weight of emulsion is pumped from the emulsion tank by means of a positive displacement pump into the mixing auger where the mixture is blended together by the action of the auger.

If needed for oxygen balance, diesel fuel is also metered into the mixing auger. The blended mixture is then discharged from the auger into the borehole. If the borehole is wet, the ratio of emulsion to ANFO is increased until the blend can be pumped. The final blend is then pumped to the bottom of the borehole through the hose.

In mining or quarrying operations with little or no water, the mix trucks do not utilize a hose reel and pump but simply have the capability to blend the emulsion with AN or ANFO and auger load the final blend into the borehole. If boreholes contain water, manufacturers normally recommend pumpable blends, containing sufficient emulsion for water resistance. Proper blend pumping techniques (See chapter 19) prevent water entrapment in the explosive column.

Energy

Blends offer the user a wide range of explosive densities and energies to adjust blasting for optimum benefit. The energy of Heavy ANFO blends and ANFO are compared in figure 12.28.

Physical Properties and Performance Characteristics

By their very nature, blends are a product line with highly variable physical properties and performance characteristics. The rheology and consistency of blends are illustrated in figure 12.29.

Manufacturer's Specifications Since blends are mixes of (1) emulsion or water gel, (2) ANFO, (3) or AN prills, their physical properties and performance characteristics may vary according to these ingredient qualities. The reader is encouraged to consult their local manufacturer or supplier for technical advice for resulting product and use specifications required when blending.

Blend Products

Blend products lend themselves to packaging and bulk blending. The size and economy of the blasting operation will normally dictate which form is practical and economical.

Packaged Blends

Packaged blends can normally be loaded into boreholes containing water with a minimum of problems, since the base density is normally in the range of 1.15 grams/centimeters³ or higher so they will readily sink. Also, since due to their packaging these blends are inherently waterproof, pinholes leaks or ripped bags may be a concern if the blend product does not contain sufficient emulsion to ensure product water resistance. If the blend is water resistant, the bags lessen handling site packages to ensure they do not bridge the borehole or float to the top of the water. In some cases, when the water is not too deep, packaged product is loaded into the borehole until the packages rise above the water level and then bulk ANFO or Heavy ANFO is loaded.

Bulk Blends

Blends with a full range of properties and performance characteristics are easily mixed in bulk trucks as discussed in the manufacturing part of this section. General bulk loading techniques are discussed in chapter 19 and the various bulk truck capabilities are discussed in chapter 20. When low emulsion content Heavy ANFO products are used in wet environments, boreholes should be dewatered and lined with sleeves as discussed in chapter 24. When boreholes can be dewatered and stay dry, Heavy ANFO products can be loaded directly into the borehole. If water cannot be removed, the blaster is advised to consider a waterproof pumpable product. Poor results quickly erase any economy of product. The rheology and consistency varies considerably among bulk blend products.

BOOSTERS

Boosters are an integral part of the blasting system. Along with an initiating device they form the primer. The primer is responsible for delivering the minimum required energy to the explosive charge to provide detonation. Often the literature discusses the essential physical and performance properties of the primer. In some small diameter applications, an initiating device may serve as the priming mechanism. If so, it must deliver sufficient priming energy. In most cases it is the booster that provides the required energy to initiate the explosive charge. Specific characteristics will be discussed below. Since boosters are a key primer component, booster selection must be made with regard to the priming requirements recommended by the explosive manufacturer.

The development of ANFO products, and later, water gel and blasting agents, created a need for high-velocity, high-energy boosters. The development of non-cap-sensitive emulsions blasting blends continued the need for these highly energetic boosters.

It has been accepted practice that, for the most efficient priming, the blaster should use the largest diameter primer that can be loaded into the borehole.

A basic property of boosters is that they impart sufficient energy to the explosive charge to create full detonation as fast as possible.

The cylindrical and cartridge shaped boosters can for all practical purposes be considered to be non-directional and adequate for the priming task as long as they meet primer requirements and are fully embedded in the explosive charge. When they approach in size the cross-sectional diameter of the borehole their priming effect is optimized. In smaller diameter boreholes where cartridged products or the detonators themselves are primers the directional effect of the detonator is important. The blaster needs to ensure the detonator is properly inserted in the booster or borehole. Primer assembly is discussed in chapter 19.

The three basic factors that determine the effectiveness of a priming system are (1) energy, (2) detonation pressure, and (3) water resistance. In addition, the efficiency of the priming system is related to other considerations including the size of the booster and the initiation system's compatibility with the main charge of explosives.

Energy

A booster must have sufficient energy to initiate the detonation reaction in the main charge and sustain it until the primed explosive produces enough energy to support the detonation reaction by itself. The energy of the booster is derived from "energy density" (energy per volume) and size. As the difference between the diameter of the booster and the diameter of the borehole becomes greater, the detonation pressure and the energy density of the booster must be increased to maintain adequate priming. If the difference is too large, the priming may be inadequate, and the primer size must be increased.

Detonation Pressure

The role of detonation pressure is known to be very important in the initiation of other explosives. As a general rule the detonation pressure of the booster should exceed the detonation pressure of the explosive being primed. Under certain circumstances, a booster with less than the detonation pressure of the receptor charge (the explosive being initiated) may initiate that charge. However, this is usually at less than steady state velocity, requiring a longer time for the explosive to run up to steady state, or full, velocity. During this elapsed time (and thus length of borehole), the explosive does not develop full pressure or maximum brisance. Under certain special conditions, the steady state velocity may never develop and the explosive will detonate at low order or, more likely, completely fail.

Detonation pressure is a critical performance characteristic of the booster. The expression to calculate detonation pressure is discussed in chapter 11. Detonation pressure is a function of detonation velocity and density, key booster qualities (See chapter 11 for a discussion of and the calculation of detonation pressure).

It is important to note that the variable VOD is squared in the detonation pressure equation. This means that that a slight change in VOD produces a significantly greater change in detonation pressure than density change. The reader to VID for the functional performance characteristics of the booster. Figure 12.29 illustrates the run up to steady state velocity for ANFO with various primers.

It is very difficult to measure detonation pressure directly. Several methods have been employed with some success but they require expensive test equipment and complex interpretation. The blaster should use the detonation pressure calculation discussed in chapter 11.

Water Resistance

Since most primer systems are placed at the bottom of a borehole where water would be found, the water resistance of the primer system should be sufficient to withstand exposure at these depths and the times required in the blasting situation. Most explosives products designated as "boosters" meet this requirement.

BOOSTER PRODUCTS

Various 1.1D explosives products can be used as a booster in the primer assembly as long as they deliver the sufficient energy required by the explosive charge.

Manufacturer's Specifications Various manufacturers produce products for suitable use as a booster for the blasting industry. Their physical properties and performance characteristics may vary according to their intended use. The reader is encouraged to consult their local manufacturer or supplier for available product specifications, transportation, storage, and use requirements.

Cast Boosters

Cast boosters are detonator sensitive explosives that typically contain the high explosive TNT as the casting material. Different molecular explosives are mixed into the melted TNT and impart additional energy and/or sensitivity to the booster. Molecular explosives are energetic materials that contain all the elements for a detonation reaction in the molecules of the explosive.

Cast boosters have been made with different shapes and sizes for different applications (see figure 12.31). Taller cylindrical boosters are designed to be initiated with detonators and can also accommodate up to 10.5 centimeters (4.75 inches) long. Some of these boosters can also be used with some detonating cords, giving them more universal appeal. Pentolite cast boosters like those shown in figure 12.32 are suited for underground blasting applications.

The lower profile boosters are designed to be initiated with only detonating cords. This reduces the range of applications for these boosters but allows the mass to be spread across the diameter of the booster. For this reason, the low profile booster better matches the diameter of a borehole than does a taller unit of compatible weight.

For example a 0.45 kilogram (1 pound) high profile cast booster usually has a diameter of approximately 57 millimeters (2¼ inches) while a low profile cast booster of the same weight will have a diameter of 76 millimeters to 100 millimeters (3 inches to 4 inches). This match of the booster diameter to borehole diameter improves the initiating efficiency of the booster. For all practical purposes the cylindrically shaped cast boosters can be considered non-directional.

General cast booster physical properties and performance characteristics are given in table 12.5.

Table 12.5 – General cast booster characteristics.

Smaller boosters at 6.8 gram to 20 gram (0.013 pound to 0.044 pound) weights are used in underground operations for smaller diameter boreholes. They have high-energy and high-density detonation pressure characteristics similar in larger cast boosters, and can be stored for long periods under various moisture and thermal conditions associated with different underground operations. Due to the high energy, heat and velocity characteristics of these cast boosters they are not allowed to be used in mines or other underground operations which require "MSHA Permissible Explosives." See Permissible Dynamites on page 189.

Not all the types of cast boosters possess the sensitivity required to be initiated by electric detonators and various strengths of detonating cord. The cast booster manufacturer should be consulted concerning the planned initiation system.

Pentolite Cast Boosters

Pentolite is a mixture of pentaerythritoltetranitrate (PETN) and TNT used to make cast boosters. The typical formulation contains 50% PETN and 50% TNT and detonates at approximately 7,400 meters/second.

Composition B Cast Boosters

Composition B is a mixture of cyclotrimethylenetrinitramine (RDX), trinitrotoluene (TNT) and approximately 1% wax, used to make cast boosters. The typical explosive formulation contains 60% RDX and 40% TNT and detonates at ~7,850 meters/second (25,000 feet/second).

Torpex Cast Boosters

Torpex is a mixture of cyclotrimethylenetrinitramine (RDX), trinitrotoluene (TNT), approximately 18% wax and 18% aluminum. The typical explosive formulation contains 41% RDX, 41% TNT and 18% aluminum. Torpex detonates at ~7,600 meters/second (24,900 feet/second).

Amatol/Sodatol Cast Boosters

Amatol is a mixture of ammonium nitrate (AN) and trinitrotoluene (TNT). Sodatol is a mixture of sodium nitrate (SN) and trinitrotoluene (TNT). These formulations are water sensitive and rarely used where the cast booster could be exposed to moisture.

Tetryl or Tetrytol Cast Boosters

Tetranitromethylaniline (tetryl) is a high brisance explosive typically used as a booster unit for other high explosives or as a pressed base charge in detonators. A pure tetryl cast booster is rarely used. Tetrytol is a possible mixture of Tetryl and TNT. Sensitive mixtures of tetryl or tetrytol boosters are most commonly used as donor charges in laboratory tests.

Slider Cast Boosters

This type of cast booster provides for an in-hole delay and requires a change in the design of the booster canister. Slider boosters are used in borehole columns that are separated by decks of inert stemming material.

PBX or Extruded Boosters

There have been various extruded boosters on the U.S. market in the recent past, which may still be available in some areas. An example of a plastic bonded explosive (PBX) is plasticized pentaerythritoltetranitrate (PETN) units seen assembled through an outdoor door lens form rubber tubes of explosives (see figure 12.31). The two principal types of extruded boosters available use either (1) designed to accept a detonator with initially a punched or used to reduce the chance of the detonator passing through and beyond the body of the charge, or (2) a cylindrical hole with an open end, which accepts a detonator if the detonator is secured in to the charge. The detonator may be secured with tape by passing the detonator through the tube, around the outside of the explosive and back into the same end. The wires or tubing may be pulled tight to ensure the security of the detonator. Manufacturers of these boosters should be contacted for specific recommendations concerning the arming of these explosives.

BINARY EXPLOSIVES

Binary (two component) explosive products as shown in figure 12.34, are typically not classified as an explosive until two commercially manufactured prepackaged components are mixed and given the appropriate time to arm. The typical binary explosive is made up of a solid oxidizer component and a flammable liquid component. Combined they form the oxidizer fuel relationship that can function as a detonator sensitive high explosive.

The unmixed ingredients of this type of explosive are generally not subject to the transportation requirements applicable to Class 1 hazardous materials (explosives). Therefore, they may be transported in the United States in unplacarded vehicles by driver's who do not possess U.S. Department of Transportation commercial drivers licenses (CDL). Also, the unmixed ingredients do not need to be stored in an approved and licensed explosive storage magazine. These storage and transportation benefits have made binary explosives extremely popular with industrial and delineating operators. Disposal (UXO/OD) contractors for law and transporter crews, utilities, agriculture and law enforcement applications, and within the Unexploded Ordnance and Explosives Ordnance Disposal (UXO/EOD) community.

Binary explosive products make a great single charge application choice, as they possess both relatively high VOD (via the liquid) and robust displacement qualities (via the solid ammonium nitrate component). Binary explosives can serve as a reliable booster to initiate blasting agents in both bulk and cartridged forms. Keep in mind that standard priming principles do apply, so matching the appropriate binary booster diameter to the borehole diameter is critical to success.

Manufacturer's Specifications Binary explosives are unique products with specific application to the blasting industry. Their physical properties and performance characteristics vary according to their intended use. The reader is encouraged to consult their local manufacturer or supplier for available product specifications, transportation, storage, and use requirements.

When used in combination with blasting agents, there are more storage options relative to established storage distance criteria since only the finished mixed product is an explosive product. Its unique transportation requirements can eliminate some of the costs associated with transporting typical high explosive products. In addition binary products can be shipped by way of a third party common carrier, potentially reducing delivery costs for smaller users.

Binary products can be safely stored together. But all users must recognize that these products are explosive precursor materials and the individual components must be stored in a safe and secure location. Additionally, users also have the option of locking them up separately for added security.

Caution The use of binary explosive products does not relieve the blaster of federal, state, provincial or local blasting rules or regulations.

Typical physical properties of binary explosives are given in table 12.6.

Table 12.6 – Typical Properties of binary explosives.

Weight values are provided in U.S. units.

LOW EXPLOSIVES

Low explosives are a high explosive alternative to safely and efficiently break rock and concrete in the mining, civil engineering, construction and demolition industries. Additional rock breakage products for the blaster to consider are: (1) explosive energetic methods using high explosives (UN 1.1) – confined and unconfined; (2) deflagration with low explosives (UN 1.4) – with rapid gas generation, propellants; and (3) non-explosives, gas propellant generators or devices for producing rapid gas generation are often chosen to fracture rock and concrete. Low explosives have many features that provide benefits in their applications. These are summarized in the tables 12.7 and 12.8.

Caution The use of low explosive product does not relieve the blaster of federal, state, provincial, or local blasting rules or regulations.

Table 12.7– Low explosive product features.

Table 12.8 – Low explosive use benefits.

Composition

Low explosive fillers are loaded into fixed-diameter and predetermined weight, water resistant cartridges. Applying stringent filler selection criteria, finished products do not transition from deflagration to detonation under confinement. Some energetic materials can detonate under pressure when ignited by a spark. Low explosive, non-detonating, energetic fillers are determined by, but not limited to, applicable regulatory authority having jurisdiction. Fillers include those listed in table 12.9.

Table 12.9 – Low explosive filler materials.

Electric or nonelectric initiation products are manufactured as cartridges as finished units for safe use, minimizing field assembly. Most finished units fire instantaneously. Low explosive gas generating propellants and pyrotechnic energetic materials are typically control initiated from a safe stand-off distance.

Energy

Low explosive energetic propellants produce rapid gas expansion and no brisance fracturing. Typically, one gram of propellant can produce one liter of gas volume when initiated. The specific energetic, composition, method of initiation, burn rate and confinement regulate the amount of gas volume and subsequent pressure generated. Unconfined initiation releases energy slowly, producing less than optimum results and confined initiation releases energy faster, producing optimum results. Adequate confinement can produce desired fragmentation and preconditional breakage of rock and concrete. Low confinement causes energy to vent to seams, voids, laminations, cracks and stemming ejecta that will result in minimal fragmentation.

Physical Properties and Performance Characteristics

Typically, low explosives are packaged on round diameter, water resistant, self contained cylindrical cartridges containing varying weights of propellant.

These cartridges are inserted into boreholes of a specific diameter and adequately stemmed, then fired. Optimal fragmentation/displacement is determined by the specific low explosive product selected, cartridge size energetic weight, and confinement. The blaster must be knowledgeable about rock hardness, laminations, voids, seams and intact rock structure. The rapid release of confined gas will find the weakest features, vent, and cause fragmentation and displacement. The specific manufacturer must train blasters on selected product use and limitations.

Manufacturer's Specifications Various manufacturer produce low explosives for use in the blasting industry. Their physical properties and performance characteristics may vary according to their intended use. The reader is encouraged to consult their local manufacturer or supplier for available product specifications, transportation, storage, and use requirements.

Caution Safe measures must be implemented to minimize weather venting, air blast and flyrock.

REFERENCES

Keleti, Cornelius. 1985. Nitric Acid and Fertilizer Nitrates, Marcel Dekker, Inc., New York, NY and Basel.

Miron, Yael. Blasting Hazards of Gold Mining in Sulfide-Bearing Ore Bodies, Information Circular 9335, US Department of the Interior and US Bureau of Mines, 1992.

ADDITIONAL RESOURCES

International Society of Explosives Engineers. 1998. ISEE Blasters' Handbook™, 17th Edition. ISEE, Cleveland, OH.