Rock Excavation

Engineering
MND400

Indian Institute of Technology (ISM) Dhanbad

 DEVELOPMENT IN EXPLOSIVES

• NG was invented by Subrero in 1846

• Dynamite by Alfred Nobel in 1863
• AN as an explosive was invented in 1940’s
• ANFO was patented in 1955
• Water-gel explosives in 1957
• Slurry explosives were developed between 1960 – 64
• Emulsion explosive were developed in 1966 – 67
• Bulk loading concept was developed in 1980
• Low density explosives were introduced - 1995
• Pyrotechnic compositions (non explosives) - 1990
 Classification of Explosives

Indian Explosive act 1983: schedule I

• Class I: Gunpowder
• Class II: Nitrate Mixture
• Class III: Nitro Compounds
• DIV I: Blasting Gelatin
• DIV II: Guncotton, PETN, TNT, Primer
• Class IV: Chlorate mixture
• Class V: Fulminate
• Class VI:
• DIV I: Safety fuse, Igniter Cord, Safety electric fuse
• DIV II: Plastic Igniter cord, detonating cord / fuse, electric fuse, fuse igniter etc
• DIV III: Detonators, Delay detonators, Relay etc
• Class VII: Firework
• Class VIII:LOX
 Classification of Explosives

According to the risk involved

• Category X: Having fire, or slight explosion risk
• Category Y: Having mass fire risk or moderate explosion risk but not mass explosion risk
• Category Z: Having mass explosion risk and a major missile effect
• Category ZZ: Having mass explosion risk and a minor missile effect
According to transport: (US dept of transport)
• Class A:Posing maximum hazards
• Class B:Posing flammable hazard
• Class C:Containing A, B or both
 Classification of Explosives

According to fume classification

• Permissible: toxic gases< 71 lit/450gms
• Non Permissible:
• I: toxic gases<0.16 ft3/200g
• II: 0.16 – 0.33
• III: 0.33 – 0.69
According to Mining purpose: used in underground
• Permitted:
• P1
• P2
• P3
• P4
• P5
 Classification of Explosives

According to sensitivity of detonation by detonator

• Cap sensitive
• Non cap sensitive
• No 8 detonator: standard detonator used for testing the explosive. It contains known amount of PETN
• If an explosive is detonated by no 8 detonator: called cap sensitive
• NG based explosive are cap sensitive
• ANFO explosive are non cap sensitive
• Slurry and emulsion explosive are non cap sensitive explosive
According to Strength
• Low Explosive: Gunpowder
• High Explosive: NG based, ANFO
TYPES OF HIGH EXPLOSIVES
• High explosive (HE)= an
explosive material that can be
caused to detonate with a No. 8
blasting cap when unconfined
• Blasting agent (BA)= a mixture
consisting of a fuel and oxidizer,
intended for blasting but
otherwise not an explosive
(cannot be detonated with a No. 8
blasting cap).
• HE’s that can be detonated
directly with a No. 8 cap are
called cap-sensitive.
• BA’s that cannot be detonated
directly with a No. 8 cap are
called cap-insensitive or non-cap-
sensitive.
 NG Based Explosives : Dynamite

• Nitroglycerine was developed in 1847

• Very Unstable
• Dynamites are explosive mixtures made of nitroglycerin made stable by dissolving it in an inert bulking
agent. The employment of dynamites has greatly diminished because of high cost ,high risk in
transportation and handling.
• Low freezing
• Ammonia
• Gelatin
• Low density
• Nitroglycerin is a dense, oily liquid that detonates if heated to 218°C or if subjected to mechanical
shock. The molecule is explosive for three reasons:
• Nitroglycerin contains both oxidant and fuel. Nitroglycerin molecules contain three nitrate groups (that
act as powerful oxidizing agents) bound directly to a glycerol fragment (which acts as a fuel)
• Hydrocarbons like gasoline usually burn rather than exploding because oxygen must come into contact
with the fuel in the combustion reaction. Nitroglycerine contains its own oxidant; doesn't have to
diffuse to the fuel to keep the reaction going
 NG Based Explosives : Dynamite
Ammonium Dynamite (1867)
• Density: 1.16 – 1.2 gm/cc
• VOD: 2750 – 4000 m/s
• Ammonium nitrate when mixed with nitroglycerine and charcoal: forms Ammonium dynamite
• Ammonium nitrate replaces some of the nitroglycerine
• Ammonium nitrate: decomposes completely, no residue left
• Ammonium Dynamite Can not be used in watery holes as it gets saturated in watery condition
• Advantage – less sensitive to shock
• Less shattering – more pushing
Straight Dynamite
• 15 to 60 % Nitroglycerine by weight
• The most unstable form
• It contains high ratio of nitro cellulose to NG to make a real rubber like water repellent
 NG Based Explosives : Dynamite
Semi gelatine dynamite
• Density: 0.94 – 1.29
• VOD: nearly 4000 m/s
• It is mixture of Ammonia gelatine + ammonia dynamite
• It is partially jelly
• Cheapest among all NG based explosive
• Gives all properties of explosive
• Widely used
Permissible dynamite (Blasting Gelatine)
• Strength is reduced by addition of Nacl2
• Hygroscopic
• These are permitted type of explosive
• P1 – strongest: 45 % of BG
• P3 – 42 % BG
• P5 – Safest: 38 – 39 % BG
 Blasting Agents
• These mixtures, with few exceptions, do
not contain ingredients classified as
explosive. The following are the most
common:
• ANFO,
• ALANFO,
• Slurries or water gels,
• Emulsions,
• Heavy ANFO.
• BA’s are either dry (free- running) or wet
(pourable). Wet BA’s are formulated with
water to achieve a density greater than
1.0
 Dry Blasting Agents: ANFO
• Dry BA’s comprise blasting-grade prilled AN (as the oxidizer), of grain
sizes between 1 to 2 millimeters in diameter and porosity between 8 to 12
percent, onto which is absorbed diesel oil (FO, as a fuel).

Ammonium Nitrate + Fuel Oil = ANFO

• To achieve oxygen balance, the ANFO mixture should have:

• 94% AN and 1 - 2 mm
• 6% FO.
• The density of the loose-poured or bulk blasting-grade AN is
approximately 0.80 g/cm3
• Today, ANFO is the most widely used explosive in the blasting industry,
because it is relatively inexpensive and safe to handle
Dry Blasting Agents: ANFO
• Explosive-grade prills are made in a prill tower in which a hot,
supersaturate AN liquid (4-percent water)—along with other additives
Prill tower ~ 200 feet tall to achieve porosity—is dropped from spray nozzles at a height of 100
spray nozzles to 200 feet against an updraft of warm air.
• Droplets of the AN solution crystallize as they fall; the longer the
droplets of
supersaturated
droplets are suspended, the larger the prill diameters.
AN solution • The crystallized AN particles are then completely dried and coated with
surfactants and clay to minimize porosity and protect the surface from
absorbing water in preparation for fuel absorption.
crystallized AN
• Porosities range from 8 to 12 percent, whereas solid-grain densities
updraft of warm
range from 1.3 to 1.5 g/cm3. Particle sizes range from 0.83 to 2.3 mm
air in diameter. By comparison to explosive-grade prills, agricultural-grade
prills are less porous (3- to 5-percent porosity) and far more dense.
 Dry Blasting Agents: ANFO

• The advantages of ANFO are:

• It is cheap
• It is easy and safe to manufacture and
• It may be handled in bulk to save costs.
• The disadvantages of ANFO are:
• It is not water-resistant
• Its density is low
• It is non-ideal reacting and
• It is not cap-sensitive and must be initiated with a primer.
 Dry Blasting Agents: ANFO
• Properties of Dry- ANFO is influenced by:
• Percentage of FO
• Density
• Confinement
• Water condition
• Charge diameter
• Coupling ratio.
• At zero oxygen balance its VOD is approx. 4200m/s
• Excess amount of FO, seriously affects its sensitivity.
• Inadequate FO generates harmful nitrogen fumes.
• Sp.gr can be varied from 0.5- 1.15 (most used range is 0.8-0.85)
• Dead density : 1.25 g/cc
• For higher sp.gr part of prills are pulvarised and mix is placed in bags
Dry Blasting Agents: ANFO

Sensitivity to initiation of ANFO

Idealized ANFO fumes versus % of fuel oil

Dry Blasting Agents: ANFO

Influence of water in ANFO performance Variation of VOD with charge diameter for
confined full coupled
charges of bulk ANFO
Dry Blasting Agents: ALANFO

• To elevate this energy per meter column length oxidizers

like aluminum is added
• When aluminum is mixed with ammonium nitrate in
small quantities, the following reaction takes place:
• 3𝑁𝐻4 𝑁𝑂3 + 2𝐴𝑙 → 𝐴𝑙2 𝑂 + 6𝐻2 𝑂 + 3𝑁2 + 1650 kcal/kg
• With the increase in percentage of aluminum, the
reaction produced is
• 𝑁𝐻4 𝑁𝑂3 + 2𝐴𝑙 → 𝐴𝑙2 𝑂3 + 2𝐻2 𝑂 + 𝑁2 + 2300 kcal/kg
• The practical limit, as far as yield and economy go, is
between 13 and 15 percent. Percentages above 25%
cause a reduction in energy efficiency

Variation of energy yield of ALANFO

with percentage of aluminum
 Wet Blasting Agents: Water-gel/Slurries
• In 1958 Cook reported the development of water-compatible bulk explosives and
their usage for underwater blasting conditions
• They consists of AN-TNT-Water
• Early slurries had densities and explosion pressures higher than ANFO but the heat of
explosions were lower
• To overcome the drawbacks of ANFO
• No water resistance
• Low density
• Low energy range
• A water-gel or slurry explosive is a gelatinous aqueous solution that consists of an
oxidizer, such as AN, and a fuel. Typically, the fuel will contain additional
dispersed solid oxidizers, fuels, and sensitizers such as aluminum or other
explosives. Wet-BA fuel may also contain micro-balloons (hollow bubbles of
glass). The difference between a slurry and water gel is that water gel is made
water-resistant by the addition of a cross-linking or chemical-bonding agent; a
slurry, on the other hand, is water-resistant (formulated to be miscible in water) by
nature
• Slurries were formed by *An example of a cap-
• Pre-dissolving the AN in small amount of water sensitive solid fuel is TNT;
• Thickening the solution by starch or guar gum (polysaccharide) an example of non-cap-
• Adding fuel component sensitive solid fuel is
• Adding the dry oxidizer to reduce overall water content
aluminum
• Some cross-linking agents to produce gels
 Wet Blasting Agents: Water-gel/Slurries
• Advantages of Water Gels
• Water gels exceed slurry explosives in that (1) they are an excellent product for wet holes and (2) the density
of a water gel can be controlled.
• Disadvantages of Water Gels
• Water gels are less effective than slurry explosives (1)at low ambient temperatures and (2) if the
supersaturated solution of AN crystallizes, causing an imbalance of oxidizers and fuels in their two phases
(that is, in their solid and liquid forms).
• Slurries entered into blasting practice in the late 1950’s
• Slurries can be either blasting agents or explosives depending upon the ingredients used
• Water in explosive – a certain amount is necessary to provide consistency and texture
• More the water content – weight strength decreases
• Less the water content – hinders the pumping
• Water content reduces the hazard sensitivity associated with fire, friction and impact
• Water content may vary from 1 to 40% , avg is 15%
 Wet Blasting Agents: Water-gel/Slurries
• In thickened slurry cross-linking agents sets up an impermeable barrier-
preventing leaching of soluble by water in the bore hole.
• With gelling and cross-linking agents desired consistence can be
produced
• Slurries categories
• Containing high-explosive fuel sensitizers
• Containing metallic fuel sensitizers
• Containing none of the high-energy ingredients.
• Sensitizers
• TNT – Organic salts (amine nitrate & perchlorates) – Fine Al powder
• Today most formulations uses mechanically or chemically generated
small air or gas bubbles
 Blasting Agents: Watergel/Slurries

Variation of strength of a typical water gel BA with Al content

Wet Blasting Agents: Emulsions
• Emulsions are “water-in-oil” mixes that were developed in the early 1960’s to improve the
performance of water gels. They amount to hot solutions of oxidizer salts (consisting of
ammonium, AN, calcium, CN or sodium, SN, and nitrates) mixed with oil and an emulsifying
agent. The oil phase usually consists of diesel fuel and/or mineral oil that include micro-
balloons as sensitizers.

• The oxidizer solution is broken up into small, micron- sized droplets, which form a
discontinuous phase within the continuous oil phase.

• The small size of the liquid-nitrated salt particles provides a large surface areas-to-volume ratio
that amounts to more fuel being placed in intimate contact with the oxidizer. This, in turn,
allows for a very fast detonation rate and a powerful explosive.

• Packaged in plastic tube or bulk-loaded from trucks, emulsions exhibit properties as follows:
• Bulk density = 1.15 - 1.45 g/cm3,
• Detonation velocity = 14,500 - 18,500 ft/sec, and
• Detonation pressure = 100 - 120 kbar
• Importance of particle size is the proximity of one unit oxidizer to one unit fuel becomes more
intimate so it increases the rate and efficiency of reaction.
Wet Blasting Agents: Emulsions
• Advantages of Emulsions
• Owing to their very small particle size, emulsion ingredients can
achieve a very uniform mix.
• Emulsions are extremely water- resistant.

• Disadvantages of Emulsions
• Over time (with long shelf life), salt crystals may grow and/or oil
migrate in an emulsion, allowing the AN liquid- phase droplets to
join and create larger droplet sizes whose bulk surface areas are
smaller. Under such a scenario, less oxidizer would be in contact
with the fuel and the sensitivity of the emulsion would decrease.
• Emulsions are expensive
ANFO/Emulsion Blends
• Blends (or heavy ANFO’s) are mixtures of emulsions and
ANFO that are typically non-cap-sensitive. As a rule, the ratio
of emulsion (or other water-based explosive or oxidizer matrix)
to ANFO in such blends ranges as.

• Packaged in plastic tube or bulk-loaded from trucks,

ANFO/emulsion blends exhibit properties as follows:
• Bulk density = 1.15 - 1.30 g/cm3,
• Detonation velocity = 16,700 - 17,500 ft/sec, and
• Detonation pressure = 40 - 55 kbar.
• Advantages of Blends
• Blends increase the density of ANFO, which increases the energy
in the borehole; they also provide water-resistance to ANFO.
• Disadvantages of Blends
• Over time, fuels may migrate and salt crystals may grow
increasingly insensitive.