Chapter 2

An Overview of Commercial Explosives

Chapter 2

;4 n Overview of Commercia{ C"EJQJ{osives

The usc of explosive for breaking rock is a technique accepted worldwide. Most of

the mining and construction operations use blasting. Many a types of mining ventures

and construction projects would not be feasible or economically justified without the

use of explosive. Coal, cement, steel, aluminum, copper and other metals are the

basic needs of any country. The supply of all these necessities depends to a great

extent on explosives.

To meet the growing demand of minerals, large open cast mines were planned. Large

open cast mining projects designed for high production rates required large size blasts

and huge quantity of explosives to be charged. The need was felt for automation of

explosive charging system to cope up with the demands of the industry in terms of

higher charging rates, less manpower, higher efficiency, low cost and complete safety.

The use of water as an ingredient in rock-blasting explosives greatly increased the

safety in processing, storage and loading. It gave a way to the introduction of

mechanical charging (bulk loading) of water based blasting agents. As a result, charging

up to I 00 tonnes of explosives in a single day could be done using 2-3 pump trucks­

a task which could not be even dreamt with cartridge explosive system (Ghose, 1991).

A major switchover from conventional packaged products to bulk delivery system

took place all over the world. Bulk loading systems have now-a-days become

synonymous with large open cast mining projects.

Many rock breaking explosives are now available in the market. In India, ANFO,

slurry and emulsion are the popular commercial explosives. All these explosives can

be used in bulk form. Emulsion explosive is a recent development in the field of

commercial explosives which has a strength of a dynamite and safety of ANFO. It has

compltely phased out the dynamite and is a threat to the other commercial explosives.

This chapter presents an overview of commercial explosives. It incorporates the

development story, a brief note on important characteristics and a short account of

4

An ( h•etTiew of ( 'ummaciul/,\p/o.l·il't'S

commonly used wmmncial explosives with spcdal reference to the emulsion explosive.

2.1 Development of Commercial Explosives

Although the usc of commercial explosives for breaking the rock began in early l 7'"

century but their large scale application has a history of only one hundred fifty years.

The history of the development of commercial explosives can be divideded into three

eras, as detailed below (see Xuguang,l994):

• Black Powder Era (1627-1870)

Black powder was invented by the Chinese about 2000 years ago and then it spreaded

to Arabian countries and Europe. The first documented proof of nitre, the basic

ingredient of black powder was found in the scripts written by Arabian author, Abd

Allah in l3'"century. In 1242, Roger Bacon published a formula for black powder.

The first documentary proof of the use of black powder for breaking the rock in

mines is by Kasper Weindl at Royal Mines ofSchemnitz at Ober-Biberstollen, Hungry.

The use of black powder for rock breaking continued until the invention of dynamites

by Alfred Nobel in 1866.

• Dynamite Era (1870-1950)

Ascanio, an Italian chemist discovered the Nitroglycerin in 1846. It was highly sensitive

to shock. Alfred Nobel invented Dynamite in 1866 by mixing nitroglycerin with

kieselguhr and named it "Nobels Safety Podwer". In 1875, Nobel formed gelatin

dynamite by dissolving nitrocellulose in nitroglycerin. Since dynamite was more

powerful than black powder, it had a higher detonation velocity and was more effective

in rock breakage; soon it replaced the black powder and dominated the market of

commercial explosives. It played an important role in rock blasting.

• Blasting Agents Era (1950 onwards)

In mid 1950s, industrial explosives entered a new development period- the modern

blasting era of blasting agents. J. R.Glauber synthesized ammonium nitrate in 1659

for the first time and named it Nitrum Flammans. In 1955, H. B. Lee and R. L. Akre

exploited the economic potential of ammonium nitrate as a blasting agent and

carbonaceous fuel sensitizer. The solid fuels, like coal, used initially were later on

replaced by fuel oil. Fertilizer grade ammonium nitrate was replaced by ammonium

5

I 'Jwprer :! All ( )l't'rl'i<'ll' of ( 'ommercia/1:\p/osil't'.l'

nitrate prills devcluped hy ( 'onsolidated Mining and Smelting Corporation, Canada.

ANH> .:aplllred the 70% of the gluhal market of commercial explosives due to its

low cost, casy prcparution and safety in usc. llowcvcr, the major disadvantages of

ANFO cxplosive arc Jack of water resistance and low bulk strength.

In !956, Prof Cook and Farnam invented slurry explosives hy mixing the aqueous

solution of ammonium nitrate with fuel and then gelatinizing the mixture. The slurries

overcame the two of the above-mentioned disadvantages ofANFO explosive. Cook

and Farnam developed a slurry with TNT and aluminum powder as sensitizer. In 1963,

lreco Chemicals, USA developed slurry explosives with non-metallic sensitizers. In

!969, DuPont, USA produced a mono-methylamine nitrate (MMAN) sensitized slurry.

In 1970s, non-explosive sensitized, small diameter, cap-sensitive and bubble-sensitized

slurry explosives came into existance one after the other. The emergence of slurry

loading trucks and pumpable slurry fulfilled the needs of surface mines for high charging

rate.

The initial form of the emulsion explosives was developed by R. S. Egly in 1961 by

mixing water-in-oil emulsion with ordinary water bearing slurry explosives. In 1963,

N. E. Gehrig developed the emulsions without slurries. In 1969, H. Bluhm of Atlas

Chemical Industries Limited fully described the technique of emulsion explosives.

Therefore, it is generally believed that emulsion explosives were revealed by Bluhm.

The emulsion explosives revealed by Bluhm, were non-cap sensitive and initiated with

the help of booster charge. In 1972, G. R. Catermole of DuPont described a formula

which increased the detonation sensitivity of the emulsion explosives by using organic

amine nitrates. This type of emulsion could detonate steadily in small diameter blast

holes. In 1973, Charles G. Wade oflmperial Chemical Industries Inc. patented emulsion

explosives containing entrapped gases and emulsion explosives containing strontium­

ion explosion catalyzer, which improved detonation sensitivity of the emulsion

explosives. In 1973, E. A. Tomic ofDu Pont patented a technique to manufacture

free-flowing, water-in-oil emulsion explosives by using ammonium stearate or alkali

stearates as emulsifier. In 1977, Charles G. Wade of Atlas Powder Company

developed a cap sensitive emulsion explosive which did not contain explosive sensitizer

and other organic amine nitrate sensitizer. The sensitization was achieved by maintaining

proper grain size and by using hollow glass micro-balloons.

In I 978, Wade published another patent about continuous manufacturing equipment

and techniques. Afterwards, many a new patents on controlling techniques for emulsion

6

( 'hllf'lt'f" } .·In ( Ji·erl'iew o/ ( ·olll!llerciall::rp/osiw.,·

density, compound cmulsilio:r. emulsifying equipment and proccss.tidd cmulsionloading

truck. water free emulsion explosiws. emulsion gelatin explosives and emulsion ANFO

explosives were published

2.2 Characteristics of Commercial Explosives

I:xplosivcs arc characterized by their properties such as strength, density, velocity of

detonation, detonation pressure, water resistance, sensitivity, thermal stability, fume

characteristics etc. These properties have been described below:

2.2.1 Strength

Strength is a measure of the ability of an explosive to do useful work. It refers to the

amount of energy stored in an explosive. Strength is generally expressed as absolute

weight strength, absolute bulk strength, relative weight strength and relative bulk

strength(see Nitro Noble, 2002).

• Absolute Weight Strength (AWS)- It is a measure of absolute amount of

energy in calories available in a unit mass of explosive. This is a theoretical

absolute heat energy based on the ingredients of the explosive and is generally

quoted in kcallkg of explosive. AWS of ANFO is 930 kcal/kg for 94% AN

and 6% fuel oil.

• Absolute Bulk Strength (ABS)- It is a measure of absolute amount of energy

in a unit volume of explosive. ABS of an explosive is density times the AWS.

It is expressed in kcal/m3•

ABS =AWS X p exp exp exp

• Relative Weight Strength (RWS) - It is a measure of the energy available in

a given weight of explosive compared to an equal weight of ANFO. (RWS for

an explosive is the ratio of AWS of the explosive to AWS of ANFO, expressed

as a percentage).

RWS.,.= (AWS.,/AWSANF0 )xl00%

• Relative Bulk Strength (RBS)- It is a measure ofthe energy available in a

given volume of explosive compared to an equal volume of bulk ANFO at

0.8lglcc density. (RBS for an explosive is the ratio of ABS of the explosive to

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( 'haJ!It'r l .·In 0l't'rl'iell' of ( 'olll/1/t'l'cia/ f.\p/osil't'.\'

ABS ofANHl, cxpn:sscd as a percentage).

RBS.,,. (ABS .. ,/ ABS,". 0 )x l 00%

2.2.2 I>cnsity

Density is defined as the mass per unit volume and in practice, it is expressed in

glee. Density of explosives is an important characteristic because explosives are

purchased and used on weight basis. It has an influence on sensitivity and the VOD of

an explosive.

The prime purpose of varying the density of an explosive is to enable the total energy

charge in a blast hole to meet the particular field conditions. In case of hard massive

rocks, denser explosives are used since more energy is required to break them. In

watery holes also, the explosive should have a density higher than that of water,

otherwise they will float.

A useful expression of density, particularly in case of bulk products, is the loading

density which is the weight of the explosive per unit length of the hole. This helps in

determining the weight ofthe explosive loaded per running meter of blast hole.The

densities of most of the commercial explosives vary between 0.8 and 1.35 glee.

2.2.3 Velocity of Detonation (VOD)

Velocity of detonation is the rate at which the detonation wave travels through an

explosive column. It is expressed in mls. It is an excellent means for checking the

explosive performance. The VOD of a blasting agent depends heavily on formulation

characteristics,confinement,blast hole diameter and priming (Bilgin & Essen, 2005).

VODs of the most of the commercial explosives vary between 2000 and 5500 m!s.

2.2.4 Detonation Pressure

The detonation pressure is a near instantaneous pressure derived from the shock wave

moving through the explosive column. It is the pressure in the reaction zone behind

the detonation zone, at the C-J plane. It is expressed in kilo bar. The detonation

pressure is important since it controls the stress level in the rocks. The stress level is

important for fragmentation.

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.·In ( h·en·iell' o/ ( 'ommercia/1:\p/osil·e.,

2.2.5 Water Resistance

Water resistance is the ability of an explosive to withstand exposun: to water without

any detrimental effects on its performance. Explosive products have two types of

water resistances; internal and external. Internal water resistance is delined as the

water resistance provided by the explosive ingredients themselves. External water

resistance is provid.:d not by th.: .:xplosivc ingredients themselves but by the packaging

into which explosive is placed. Water can either dissolve in or leach out some of the

explosive ingredients or reduce the temperature to such a degree that the ideal products

of detonation may not form even though the explosive is oxygen balanced.

2.2.6 Sensitivity

The sensitivity of an explosive is the amount of input energy needed to cause a reliable

initiation of the explosive. It is also called the minimum booster rating or minimum­

priming requirement. Sensitivity of an explosive is affected by the presence of water

in blast hole, inadequate charge diameter and extreme temperature conditions.

2.2. 7 Temperature Resistance

Explosive compounds can suffer in performance if they are stored under extremely

hot or cold conditions. In hot storage conditions, beyond 90°F, many compounds

may slowly decompose and change their properties. Most of the commercial explosives

contain ammonium nitrate. Storage of ammonium nitrate based blasting agents in

temperature above 90°F can result in cycling which affects the performance of the

product. Cycling is the ability of a material to change its crystal forms depending on

temperature. The two temperatures at which cycling will occur in ammonium nitrate

are 0°F and 90°F (Konya & Walter, 1990).

Cold conditions can also affect the performance of some explosive products. Some

products may become stiff and firm after prolonged exposure to a low temperature

and may become difficult to use in the field. Slurry explosives can have serious

detonation problem if stored in cold temperature and is not allowed to warm up before

they are detonated (Konya & Walter, 1990).

2.2.8 Fume Characteristics

The fume characteristic of an explosive is a measure of the amount of toxic gases

produced in the detonation process. Carbon monoxide and nitrogen oxides are the

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An ( h·erl'it'\1' of ( 'ollllllt'rL'ial F\p/osil•e.1·

mDsl common gases that an: consitkred in the fume class rulings. ( 'arhon dioxide is

nDt considered as fume since it is not toxic. llowever, it can result in death due to

su!Tocation if generated in large quantity during blasting in the con!incd area.

Commercial cxplosiv.:s an: oxygen balanced to minimize fumes. However, fumes can

still occur as a result of hlast environmental conditions such as insuf!icient charge

diameter, inadequate water resistance and inadequate priming ( Konya & Walter, 1990).

2.3 Commercial Explosives

The commonly used commercial explosives in India are ANFO, slurry and emulsion.

Dynamite is completely phased out from the market. All these explosives are available

in bulk form. The properties of these explosives have been summarised in Table 2.1.

Bulk emulsion explosive is dominating the market of bulk products in India and is

being used by all major explosive consumers namely; Coal India Ltd., National Mineral

Development Corporation, Singreni Collieries Company Ltd. etc. Market ofbulk slurry

is restricted only to few mines of Coal India Ltd., Hindustan Copper Ltd. and National

Mineral Development Corporation. The use of bulk ANFO (mechanically loaded) is

limited only to bauxite mine ofNational Aluminum Company Ltd. Manually loaded

ANFO is popular among small mine operators and construction work. Slurry is leading

the market oflarge diameter cartridge explosives (LD explosive). Production of these

explosives in India in the year 2002-03, 2003-04 and 2004-05 is given in Table 2.2.

A brief description of these explosives is given below with special emphasis on the

emulsion explosives.

2.3.1 Ammonium Nitrate-Fuel Oil (ANFO)

ANFO, also known as dry blasting agent, is a simple physical mixture of prilled

ammonium nitrate and fuel oil (diesel oil) in the ratio 94:6 by weight. ANFO is still the

most popular explosive in the world because of its low cost, but in India, it is not such

popular because of the non availability of prilled ammonium nitrate in sufficient quantity.

In India, it is mostly used by small mine operators and in civil construction projects as

manually site mixing form. Though, ANFO has a high weight strength (930 kcal/kg)

and a good gas volume, it has several drawbacks such as low density, low VOD, low

bulk strength, low detonation pressure and very poor water resistance. It is not suitable

for use in hard, dense, massive rocks and watery holes. But in soft to medium hard

rocks and in jointed strata, where heaving action is preferred, it works very well.

10

I 'hapra:! An Own•iew tJ(( 'ommercia/l:~rp/Mive.\·

'l(thlt: :?..1 : Properties of Bulk bplosivcs (l'radhan, 1996: Pradhan & Kate, 2005).

Property ANFO Slurry Emulsion Physical condition Powder Slurry_ Greasy emulsion Oxidizer Prilled AN Liquid salt solution Liquid salt solution Initiation Booster Booster Booster Impact sensitivity, 3-3.5 >10 >10 kgm Density, glee 0.8-0.9 0.65 to 1.1 ,variable 1.0-1.3, variable VOD, m/s 2400-4500 3000-4500 4000-5500 RBS (%AN) 100 110-135 135-150 RWS (%AN) 100 80-100 100-120 Energy, kcal/kg 930 600-1100 600-850 Water resistance Poor Excellent Excellent Low temperature 32.2 4.0 4.0 resistance, °C High temperature < 100 100 100 resistance, °C

Table 2.2 :Production of Explosives in India in the Year 2002-03, 2003-04 & 2004-05

(Petroleum and Explosive Safety Organisation).

Sr Description Production, Tonnes No 2002-03 2003-04 2004-05 A Blasting Explosives

Gun Powder: 123 295 515 Nitrate Mixture: Permitted Small Dia. (SD) 19103 25511 22857 Non Permitted Small Dia. (NPSD) 15034 29787 43312 Large Dia. (LD) 106249 108664 98855 Site Mixed Bulk Explosives 215645 217120 190924 ANFO (Manufactured and used) 14051 14315 26094 Total Class 2 370205 395692 382557 Nitro Compounds: Permitted Small Dia. (SD) 3992 2984 ---

Non Permitted Small Dia.(NPSD) 23943 20023 ---Large Dia. (LD) 2515 299 ---Booster 1189 873 875 Total Class 3 31639 24179 875

B. Safety Fuse (million meter) 99 155 109 C. Detonating Fuse (million meter) 135 164 209 D. Detonators (million number) 451 419 432

II

( 'hupl.:r :! An Ol't'rl'iew oj ( 'ommerciul Exp/o.l'i\'1!.\'

2.3.2 Slurry Explosives

Slurry explosives wen: lirst developed as a result of attempts to water proof, improve

the density and strength of ANFO. Slurry is a mixture of nitrate (such as ammonium

nitrate and sodium nitrate), a fuel sensitizer either explosive or non explosive and

varying amounts of water. The mixture is thickened with guar gum to slurry consistency

and cross linked with some transition metal ions to form an effective gel matrix.

Slurry explosives are available both in bulk and cartridge form. Cartridge slurry

explosives are available as both cap sensitive and non-cap sensitive. They exhibit an

excellent water resistance. Their VODs vary from 3000 to 4500 m/s. Since they are

water based explosives, they are less sensitive to shock and friction and are extremely

safe in transportation, storage and use.

2.3.3 Emulsion Explosives

Emulsion explosives have become quite an important blasting means because of their

comparatively high detonation parameters and exceptionally good safety characteristics.

Emulsion explosives are prepared by agitation the of a super saturated aqueous solution

of some oxidizers and a fuel doped with an emulsifying agent. The composition thus

prepared is extremely insensitive to initiation and hence requires gas bubbles for

sensitization. The basic oxidizer used in emulsion explosives is ammonium nitrate.

Sodium nitrate and calcium nitrate are frequently used to modify the properties of the

oxidizer solution. The fuel phase consists of various mineral oils and waxes. A

distiguinshed feature of emulsion explosives is that in the aqueous solution, the oxidizer

is present in the form of tiny droplets covered with a very thin fuel layer. Consequently,

the interfacial surface of the emulsion is very large, as a result of which emulsion

explosives have high VOD. The VOD of emulsion explosives vary from 4000 to 5500

mls.

• Composition of Emulsion Explosives

Emulsion explosives are multi component explosives. They essentially consist of an

aqueous solution of oxidizer salts, fuel, emulsifier, density modifier and small amount

of additives. The main components of an emulsion explosive with their functions are

discussed below (see Xuguang, 1994 ):

12

( 'lwpter 2 An ( >wrview ofC 'ommerdul fxp/osive.1·

• Oil-phase Material

The oil-phase material is one of the key components of emulsion explosives. It is a

group of water-insoluble compounds which form a water-in-oil emulsion together with

an aqueous oxidized salt solution in presence of an emulsifier. The primary functions

of oil-phase material are to form continuous phase of emulsion in an emulsion explosive

system and to act as a combustion agent. It also provides water resistance and

consistency to the emulsion explosive system. Any hydrocarbon having a proper

consistency can be used as an oil-phase material for emulsion explosives. All waxes,

oils and various polymers are commonly used in emulsion explosives.

The waxes which are commonly used in emulsion explosives are the ones extracted

from petroleum such as vaseline wax, microcrystalline wax, and paraffin wax; mineral

waxes such as earth wax and montan wax; insect wax such as beeswax etc. All liquid

petrolium products having proper consistency may be used as oil phase material. The

commonly used petroleum oils are diesel oil, machine oil and vash oil.

Polymers are often used to thicken the oil-phase material. Commonly used polymers

are natural rubber, synthetic rubber, copolymers of butadiene-styrene etc. Saturated

fatty acids like caprylic acid, capric acid, lauric acid, higher alcohols like hexanol,

nonanol, lauric alcohol and some plant oils like corn oil, cotton seed oil, soybean oil

etc. may also be used as oil-phase material.

• Aqueous Oxidizer Solution

The aqueous oxidizer solution is another important component of emulsion explosives.

It provides dispersion phase to emulsion explosives and also acts as an oxidizer. It

also decides the density of the final product as it accounts for about 90% of the total

mass of the explosive.

Generally, aqueous solution of ammonium nitrate is used as a dispersion phase in

emulsion explosives but other organic and inorganic oxidizer salts compatible with

emulsion, may also be used together with ammonium nitrate. Ammonium nitrate is an

inexpensive and efficient oxidizer. It is easily soluble in water but its solubility goes

down as the temperature decreases and it leaches out from the solution thereby affecting

the stability of the emulsion explosive. The solubility of saturated ammonium nitrate

solution at various temperatures is shown in Table 2.3. To improve the stability of

emulsion, a mixture of ammonium nitrate, sodium nitrate and /or calcium nitrate is

13

( 'lwpler 2 An ( )l't'n'iew o/ ( 'ommercial l:xp/o.l·iws

Tab I.: 2.3 :Solubility of Ammonium Nitrat<: in Water at Varying Temperatures (X uguang.l 994 ).

T.:mpcraturc,"C Solubility, g In I 00 g water In I 00 g solution

() 20 54.5 10 150 60.0 20 187 65.2 30 233 70.0 40 280 73.7 50 339 77.2 60 411 80.4 70 50! 83.4 80 618 86.1 90 772 88.5

100 994 90.9

generally used to prepare the aqueous oxidizer solution for emulsion explosives. Use

of mixed salt solution increases the oxygen-supplying quantity and density and lowers

the fudge point of the explosive. The density of the powdered and grained ammonium

nitrate is usually in the range 0.8-0.95 g/cc. It supplies 200 g of oxygen per kg.

Sodium nitrate is the most common supplemental oxidizer suitable for emulsion

explosives. It raises the dissolubility and drops the fudge point of aqueous oxidizer

solution and thus improves the stability of the emulsion explosive. Its density is 2.265

glee and oxygen-supplying quantity is 2.35 times that of AN. It also increases the

density of the emulsion matrix and oxygen supplying quantity of the oxidizer solution.

Calcium nitrate is also a good supplementary oxidizer for emulsion explosives. It not

only drops the fudge point of the aqueous oxidizer solution but also promotes the

emulsification, thus improves the quality of emulsions. Its oxygen supplying quantity is

about 2.5 times more than ammonium nitrate.

Sodium percolate is also used in emulsion explosive as it is a good oxidizer and a

sensitizer. It improves the detonating sensitiveness, performance and storage stability

of the explosive.

• Density Modifier

Density modifier refers to a group of substances which can introduce a large number

of micro-bubbles into emulsion explosives. The main functions of a density modifier in

14

An 01•en•iew of ('om mercia/ Exp/osiws

~mulsion explosive arc to control the density of the explosive and to sensitize the

~xplosivc according to th.: hot spot theory of initiation.

The commonly used density modilicrs arc occluded gases, chemical foaming agents

and gas retaining closed solid particles.

Occl udcd gases refer to micro-bubbles of air, nitrogen, carbon di-oxide, nitrogen

monoxide, gaseous hydrocarbons etc. retained and evenly distributed in emulsion

explosives by mechanical stirring.

The chemical foaming agents are those agents which can enter into a chemical reaction

and hence produce a large number of micro-bubbles, evenly dispersed throughout the

explosive. The chemical foaming agents are of two types-inorganic and organic. The

inorganic foaming agents include nitrites such as sodium and potassium nitrites,

carbonates such as sodium hydrocarbonates, ammonium carbonate and ammonium

chloride. The organic foaming agents include azo compounds such as azoamino-benzene,

azo-isobutyric dinitrate and hydrazine compounds such as hydrazine hydrate etc.

Inorganic foaming agents particularly sodium nitrite is extensively used in emulsion

explosives as foaming agents. Sodium nitrite reacts with ammonium nitrate and produce

ammonium nitrite which is unstable and decomposes into nitrogen and water. Nitrogen

micro-bubbles spread through out in the emulsion and modify its density and sensitize it.

NH4NO,= N, +2H20

Gas retained solid particles added to emulsion explosives may be either glass or resin

hollow micro-balloons or expanded particulate perlite. As compared to gas-occluded

or chemical sensitization methods, emulsion explosives sensitized by this method are

able to bear tremendous external pressure. Glass micro-balloon is made up of a new

silicate material which is light in weight and has good roundness and chemical stability.

Expanded particulate perlite is a white porous loose particulate material made by

crushing, preheating and roasting acidic volcanic glass lava (perlite ore).

• Emulsifiers

Emulsifiers are one of the key components of emulsion explosives and usually their

content is 0.5 to 2.0% of the total massoftheexplosive. They play an important role in

15

( 'hapter 2 An 0\'C!rl'iell' tJj'( 'ommrrciul F.xplosive.\·

maintaining the quality of an emulsion explosive. Emulsifying efliciency of aqueous

oxidizer salt solution and carbonaceous fuel depend mainly on the type and activities

ofth.: sckcted emulsitiers.

Emulsifiers used in emulsion explosives are composed ofderivants formed by esterifying

the sorbitol after removing one mole water from it. These derivants may include sorbitan

fatty acid esters such as sorbitan mono laurate, sorbitan mono olerate, sorbitan mono

palmitate, sorbitan tristerate. Other emulsifiers which may also be used include; sorbitan

polyoxyethylene esters such as sorbitol polyoxyethylene beewax derivants and other

substances such as polyxyethylene(4) lauric ether, polyoxyethylene (2) oleyl ether,

polyoxyethylene (2) stearoyl ether, polyoxylalkylene oleic acid layrate oleic phosphate

substituted oxazoline etc.

• Other Additives

To improve the performance of the emulsion explosives, small quantities of some other

components are also added to them which are as described below:

• Crystal-shape Modifier

To control the dissolution~ crystallization balance of oxidizer salts, crystal shape

modifiers are added to emulsion explosive in the range 0.1-0.3% by weight. These are

added to oxidizer salt solution prior to emulsification. These agents include alkyl alcohol

alkali metal sulphonate, alkyl alcohol alkali metal sulphate, phenyl or naphthyl alkali

metal sulphonate and phenyl and naphthyl alkali metal sulphate. Amongst these, dodecyl

sodium sulphate, dodecyl sodium sulphonanate and dodecanol acyl phosphate are

commonly used.

• Emulsification Promoter

Highly chlorinated paraffinic-hydrocarbons are used to promote emulsification of

emulsion explosives. It also improves the detonation sensitivity and longer storage

stability of emulsion matrix. Its addition amount ranges between 0.2-0.8% of the

total mass of explosive. It is used in conjunction with carbonaceous fuel and emulsifier

in a pre-mixture form.

• Emulsion Stabilizer

To improve the long-term storage stability of emulsion explosives, emulsion stabilizers

16

< 'haf>la :! An O••en•i<!l\'11/ ( 'o111111t'rdt1/ Erp/o.•·ive.1·

an: added to emulsion explosives in small quantity. These stabilizers together with

emulsifier arc dissolved in oil-phase prior to emulsification. Some commonly used

emulsion stabilizers arc phosphatide compounds like soybean lecithin, solid tine powder,

and beeswax and borax.

Soybcan is a plant lccithin. Addition of about 0.5% of this stabilizer improves the

long-term storage stability of emulsion explosives. Solid fine powder ofzinc stearate,

tctradecoic acid zinc, aluminum stearate, tetradecoic acid magnesium, carbon black,

silicon dioxide, iron oxide, titanium dioxide, sulphur, aluminum and zinc improve the

stability of emulsion explosive in storage and performance under low temperature.

Addition amounts of solid fine powder are usually in the range 0.1-1%. Beeswax and

borax have also been found to improve the storage stability of emulsion explosives.

Addition amount of beeswax in an emulsion explosive is about 0.3% and that of borax

is about 0.4 to 0.7% of the mass of explosive.

2.4 Bulk Emulsion Explosives

Bulk explosive systems are essentially those where explosives are delivered directly

into the blast hole through mechanized and mobile delivery systems. Explosives which

are amenable to bulk loading are ANFO, slurry and emulsion. The bulk explosive

systems offer the following advantages (Pradhan, 1996; Xuguang, 1994):

• Only non-explosive ingredients are stored in all stages.

• No inventory of explosives is required to be maintained.

• Construction of expensive magazines is not required.

• No need for a large fleet of explosive vans. Explosive vans are required only

for transportation of cast boosters, detonating cord, detonators etc.

• Significant savings in manpower costs since magazine staff, van drivers,

magazine security, and blasting crew are reduced.

• Significant cost advantage since cartridging, packing and transportation from

far-off manufacturer's plant is eliminated.

• Swift charging rate upto 250 kg/min or more.

• Ability to customize explosives on site the as per the field requirement.

17

( 'lwpler 2 An ( )vervit'\1'11/ ('om mercia/ f:xp/oJive.1·

• Full bore coupling of bulk products results in beth:r blast efficiency.

• Better transfer of explosive energy to rock due to full bore coupling permits

larger spacing and burden ami thus results in reduction in drilling cost.

• No chances ofcxplosivc pilferage.

Emulsion explosives are available both in bulk and cartridge form. Bulk emulsion

explosives are booster sensitive. They are usually mixed and prepared on the site and

directly loaded into the drill holes. Basically, there are two systems for bulk delivery of

emulsion explosives namely; site mixed emulsion explosive system and re-pumpable

emulsion explosive system.

In site mixed emulsion explosive system, a support facility is erected near the mine

site where the intermediaries for the production of explosive on truck such as oxidizer

and fuel blends are prepared. The truck carries different ingredients in different

compartments. The mixing of various ingredients in pre-determined calibrated quantities

is carried out on the truck and the final mixture is pumped into the blast hole through

a loading hose. The advantage of this system is that explosive material is neither

manufactured at the plant nor carried on the truck. The mixture becomes an explosive

only after gassing that takes place in the hole. Also, explosive formulations can be

customized by controlling the addition of ingredients. The main disadvantage ofthis

system is that the pump trucks are of complex design. Moreover, quality assurance is

difficult as the emulsion matrix is prepared on the truck at the site (Persson eta!.,

2001 ).

In re-pumpable emulsion explosive system, non-explosive emulsion matrix is prepared

in a support plant erected near the mine. The non-explosive matrix is carried on the

pump trucks to the blasting site. Only gassing agent is mixed in batches to the matrix

on the pump truck just before the charging ofthe holes. The pump trucks of this

system are of simple design. In India, re-pumpable system is more popular.

2.5 Chemically Sensitized Bulk Emulsion Explosives

The bulk emulsion explosives are generally sensitized either by addition of glass micro­

balloons (GMB) or chemicals. In India, chemical gassing method is often selected by

the explosive manufacturers because glass micro-balloons are expensive and not

manufactured in India. A comparison of GMB sensitized with chemically sensitized

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t 'hapter :? An ( )t•en•iew t!(l 'ommerciul Explosive.\·

lab!.: 2.4: Comparison of Glass mi~ro-balloon Sensitized Emulsion Explosive with Chemically S.:nsitizcd Emulsion Explosive.

Parameter Gl8ss mlcro-b8lloons sensitized Chemicnlly sensitized emulsion explosives emulsion explosives

Cost Costly Cheap Size of the bubbles, 10 to 160 0.5 to I 00, Mostly 5-50 rn icron

Uniformity of More uniform size Not of uniform size bubbles Tendency to Low High agglomerate or escape Storage stability High Low Sensitive effect Good Better than Glass micro-

balloons Hydrostatic pressure Can bear high hydrostatic Can bear comparatively low

pressure. Best suited in deep hydrostatic pressure holes.

emulsion explosives is given in Table 2.4. In chemically sensitized bulk emulsion

explosives, an aqueous solution of sodium nitrite (15% by weight) is added to emulsion

matrix stream, in the range of 0.6 to 2.0% by weight just before charging of the holes

(Manka, 2004). Sodium nitrite on reaction with ammonuim nitrate from the matrix

produces nitrogen bubbles. These nitrogen bubbles evenly spread throughout the

emulsion matrix and sensitize it. Under unfavorable conditions such as low temperature

and/or high pH value, sodium thiocyanate accelarator is also added to gassing solution

to facilitate the generation of nitrogen gas. This gassing solution consists of 15-20%

of sodium nitrite, 15-30% of sodium thiocyanate and 50-70% of water by weight

(Manka, 2004).

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