Evolution of Explosives in Mining

Recent Rock Blasting Trends
Need Driven Evolution
D.Acharya
diwakar.acharya@gmail.com

Mining Eco-System
Recent Rock Blasting Trends in Mines
• Science, Regulation, Economics &
Safety exert significant influence on
mining
• Mining in turn has many major
activities: Drilling, Blasting, Hauling,
Support etc
• Interplay of various influencers are
considered in selection process of
all activities
• Trends evolve in response to
demand by the influencers
-NG explosives are not allowed
due to safety considerations

Mineral, Ore & Mining
Minerals are:
• Naturally occurring
• Inorganic
• Have definite chemical composition
• Ordered internal structure
(A mineral is composed of the same substance throughout)
Rock:
It is made up of 2 or more minerals. You need minerals to make rocks,
but not rocks to make minerals.
Ore: A mineral occurring in sufficient quantity and containing enough
metal to permit its recovery and extraction at a profit. Shape &
geometric regularity too make critical difference

Ore Geometry
(Not to Scale)
Weak Shale Roof in Kadapa Down-dip Irregularity in Saraikela-Kharswan
Irregular shape in Singhbhum-E Complete irregularity in Gulbarga

Surface Topography
Ore Bodies
F/W Band
H/W Band
TUMMALAPALLE PROJECT

Fragmentation in Weak Rock
Overcharge or higher strength
explosive will result in over-
break
• Safety concern
• Higher support cost
• Increased dilution
• Increased transportation cost
• Higher energy & consumable
cost in plant
• Occupies more space in
Tailing Pond
Explosive with low strength and
possibility of variable strength &
with less charge per delay are
preferred
Water seeping through rock bolt holes indicate
water bearing weak shale in roof in Kadapa

Ore Geometry & Blasting
• Lower dip or irregular ore
geometry requires:
‐ Shorter hole length
‐ Lesser diameter <45mm
‐ Explosive of low critical
diameter
• This in turn impacts charging &
fume clearance time
• More blasts for the same tonnage
influence mining machinery
selection
Rock Geometry
Blasting

Evolution of Blasting
Fragmentation in ancient Egypt
• Fire & rapid quenching was used for
fragmentation of rock in ancient Egypt
for construction of Pyramids
- Rock breaking for Pyramids was
too labour intensive &
unsustainable. It led to evolution
of fire as a tool
• Gunpowder- invented in China around
10th century. Was used in fireworks
and signals. Its introduction in mining,
tunnelling & civil construction was in
early 15th century
- Met the productivity need
- However only less than half the
powder mass converts to gas
Gunpowder in China

Explosives : American Classification

Evolution of Blasting
• Nitroglycerine was invented in Italy in
mid 19th century
- very strong explosive
- degrades over time & makes it
dangerous to transport & use
• Dynamite was invented by Alfred
Nobel in 1867 as the first safely
manageable strong explosive
- Dynamite combines nitroglycerin
with absorbents and stabilizers,
rendering it safe to use
- Over time, dynamite will "sweat"
nitroglycerin. Crystals will form
making it shock, friction, and
temperature sensitive
- Old dynamite is prone to blasting
accident
A. Nitroglycerin soaked
Sawdust
B. Protective coating
C. Blasting cap
D. Metal strips to hold

Evolution of ANFO
• ANFO in use since 1950’s
- Cheap & easy to use
- Constituents: 94% AN, 6% Fuel
with some Aluminium as
sensitizer, also adds energy. Cost
has discouraged its use
- AN has air in ‘prills’
• ANFO is hygroscopic. Needs
attention in UG use: easy disposal
• Low density: longer charge length
• Often incomplete reaction
• Not cap sensitive: safety in storage &
transport

Control of Weak Strata
• Crushed Zone: Zone of fine
fragmentation
• Fractured Zone: Zone of radial cracks
• Seismic Zone: Zone of elastic
deformation
Control of seismic zone is critical to manage
overbrake

Safety Perception ANFO
• Surda Coppper Mine had an ANFO
related accident on 4/4/1984
• Secondary blasting with ANFO in 10th
level
• Drillers & others were coming out
through 9th level where ventilation door
was jammed due to blast induced air
shock
• Exposure to high NOx (>100ppm) caused
5 fatalities
DGMS restricted use of ANFO in secondary
blasting
However, widespread fear stopped usage of
ANFO in entire Singhbhum mining belt
Nox with fuel
CO with fuel

Explosive & Security
OD WB
JH
• ANFO is the preferred tool of
spreading destruction from
Afghanistan to India
• The reasons for ANFO to be popular:
- These are cheap, easy to
obtain& make, safe to handle &
transport
- Easily camouflaged as
agricultural inputs
• Many mines, specially Baghjata of
UCIL are located in LWE stronghold
• Many LWE incidences in the
neighbourhood
• An alternative explosive which can
not be misused is a necessity
An example of ‘need’ driving evolution

Emulsifiers ensure
kinetic stability of
emulsions
• Emulsion explosives are the intimate & homogenous
mixture of two immiscible oxidiser & fuel phases,
stabilised with the help of emulsifier
• Internal phase is solution of Ammonium Nitrate like
oxidiser dispersed as fine droplets surrounded by a
continuous fuel phase
• Emulsifying agent stabilizes the emulsion against
separation
• Glass, resin, air or bubbles are used for controlling
sensitivity of the emulsion product
• Emulsion viscosity can be varied making it suitable for
cartridge of various sizes – for UG as well as OC
Credit: Partha Das Sharma
Emulsion Explosives

Advantage - Emulsion Explosives
• Insensitive to friction, impact, fire: Safer than NG in
storage & handling
• Oxygen Balance: Low noxious fumes
• Oil phase outside: Better water resistance than
ANFO, slurry
• High VOD is possible: Suitable for hard rock
condition
• Critical dia can be customised: Suitable for UG
• Strong mixture between oxidiser, fuel: Higher
energy than ANFO, Gel
Credit: Partha Das Sharma diwakar.acharya@gmail.com

Bulk Emulsion Explosive
• Bulk emulsion explosives dominate
opencast mining
• Its use in UG was restricted due to
small dia holes & underground
logistics
• UG bulk emulsion has 2 non explosive
components:
- Primary component is factory
built bulk “Premix”
- 2nd component is “Sensitizing
Solution”, both are mixed UG
- Density, VoD, Relative strength
can be varied by changing
concentration of the solution
- Initiated by detonator & packaged
emulsion
D e n s i t y
( g / c c )
CriticalDia
( m m )
VOD (km/s)Relative Weight
Strength(RWS)
Relative Bulk
S t r e n g t h
( R B S )
0.8 38 4.5 72 72
0.9 38 4.9 78 89
1 38 5.3 85 106
1.1 38 5.7 92 127
1.2 42 6.2 98 147

Advantage Bulk Emulsion in UG
• Faster charging rate: Charge is
pumped unlike cartridge loading
• Longer pull: Explosive strength can
be customised
• Reduced drilling: Higher coupling
ratio
• Less roof & side shatter: Periphery
can be low density, energy
• Safer handling & storage: It acquires
explosive character only after it is
loaded in the hole
• Ideal in current security scenario
• Less manpower & less persons
exposed to potentially hazardous
activity

Bulk Emulsion in Turamdih
• Better pull at 90% against average of 75%
• Reduction in No of holes by 9%, 41 holes instead of 45
• Better fragmentation
• No significant overbreak
• Reduction of 45% in charging time
• Reduction in manpower requirement

Bulk Loading in HCF
• HCF is associated with large no of
faces to be blasted in each shift
• Carrier has to move between
different faces in different levels
• Allowed fume clearance time is
between the shifts and longer
charging time disrupts all mining
activities
• Carriers are not made in India
Mining companies will have to partner
with explosive manufacturers to make
the endeavour successful

Blasting Vrs Boring
• Boring does not shatter the roof &
sides
− Less supporting time & cost
• No fumes are generated
− Saving on fume clearance time
• Muck generated is well fragmented
Saving in secondary blasting
More efficient mucking
• Very low manpower deployment
• Operator is in a safe enclosure
• Raise boring eliminates exposure to
risk from falling rock
− No one is exposed to poor
ventilation & blasting fumes in
raise

Limitations on Use
• Hardness is a limitation on
applicability (250MPa)
• Joint planes, orientation of joint
planes etc are difficult conditions for
boring M/Cs to handle
• Mining passages are not very regular
• Need long tunnels & raises to offset
long setup time
(Chennani-Nashri Tunnel –J&K)

Evolution of Explosives in Mining

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