For blast initiations

1. Presented by:
Dr Clement Kweku Arthur

2. Learning Objective
 Having worked through this chapter, the student will
be able to:
 Know and understanding the various initiation
systems

3. Initiation Systems
 An initiation system is a combination of explosive
devices and component accessories designed to
convey a signal and initiate an explosive charge from a
safe distance when properly configured and
activated.
 The signal function may be either electric or non-
electric.

4. Initiation Systems
 Electric initiation systems use electrical power source
with associated circuit wiring to convey the needed
energy.
 Non-electric systems use various types of chemical
reactions ranging from deflagration to detonation to
convey the impulse to the non-electric detonators, or
in the case of detonating cord.

5. Initiation Systems

6. Initiation Systems
 The initiation systems commonly employed in surface
blasting are:
 Safety fuse with caps (mainly in quarries for secondary
blasts),
 Detonating cord,
 Electric caps or detonators
 Non Electric (NONEL) assemblies,
 Electronics detonators and
 Wireless Electronic Blasting Systems (WEBS)

7. Initiation Systems
Initiation Through Ages

8. Capped Fuse (Safety Fuse)
 SAFETY FUSE is a ductile cord twined of cotton
threads and coated with black polyethylene plastic.
 The core of the fuse contains black powder.
 Throughout the mining world today, the capped fuse
has been superseded by the other three systems for
primary blasts due primarily to safety hazards, slow
burning rates and poor water-resistance properties.
 Safety fuse is primarily used in quarrying and in small
blasts with detonating cord caps.

9. Detonating Cord
 Detonating cord (detonating fuse) resembles safety
fuse but contains a high explosive instead of black
powder.
 The first successful one, patented in France in 1908,
consisted of a lead tube, about the same diameter as
safety fuse, filled with a core of TNT (Trinitrotoluene).
 It was made by filling a large tube with molten TNT
that was allowed to solidify.
 The tube was then passed through successively smaller
rolls until it reached the specified diameter.
 PETN (pentaerythritol tetranitrate) is another
explosive used in the detonating cord

10. Detonating Cord
 Detonating cord is a flexible but strong continuous
detonator that can be several hundred meters long.
 A length of detonating cord is required to initiate a
detonator which cannot be normally initiated by fire.
 Detonating cords are available with a variety of charge
weights, tensile strengths and protective coatings,
depending on the application.
 Their energy release depends on the amount of PETN in
the core, which generally varies from 1.5 g/m to 70 g/m.
(Detonating cord is rated in explosive mass per unit
length)
 However, 10 g/m is the PETN weight of standard
detonating cord whose VOD is about 7000 m/s.

11. Electric Initiation Systems
 Designed to be detonated by a pulse of electrical energy.
 Hence, susceptible to accidental initiation by extraneous
electricity such as stray currents, static electricity, Radio
Frequency Energy (RFE), electrical storms, and high-
voltage power lines.
 This constitute a major disadvantage of the system.
 This therefore, suggests that due consideration must be
given to the potential hazard from extraneous electricity
when using electric detonators or when choosing
electrical initiation system for blasting operations.

12. Electric Initiation Systems
 Electric detonators may be classified into 3 main groups
according to their inherent timing properties. These are:
 Instantaneous detonators. These are employed
mainly for boulder or stone blasting and presplitting,
where no delay interval between the different charges is
desired.
 Millisecond detonators. These are mainly used in
bench and tunnel blasting.
 Half-second detonators. These are exclusively for
tunnel blasting where longer delays are required to
prepare space for the movement of the blasted rock
masses.

13. Electric Initiation Systems
 Electric detonators may be connected in anyone of the
following ways:
i. In series
ii. In parallel, or
iii. In parallel-series.
 The series circuit is generally preferred because of its
simplicity. However, it requires larger current than that
for firing a single detonator.

14. Electric Initiation Systems
 In general, exploders providing DC currents are suited
for series blasting.
 Research has shown that minimum current
requirements for straight series circuit is 1.5 amperes for
Dc or 3.0 amperes for AC; and for parallel-series circuits
the minimum DC or AC current should be 2.0 amperes
in each series circuit.
 Similarly, for straight parallel circuits the recommended
minimum current per detonator is 1.0 ampere.

15. Non-Electric Initiation Systems
 Non-electric initiation systems available for open pit and
other surface blasting operations combine the
advantages of electric and detonating cord systems and
are generally referred to as NONEL DETONATORS.
 They consist, basically, of a cap similar to an electric
blast cap or detonator and having a tube that extends
from the cap similar to those of the leg wires in the
electric detonator or cap.
 Inside the tube is a powdery material that propagates a
mild detonation, which activates the cap.
 The systems are incorporated with delay periods

16. Electronics Initiation Systems
 Electronic detonators have an electronic counter on a
microchip in place of the pyrotechnic delay charge, and a
capacitor to supply the discharge energy for ignition.
 Advantages compared to regular electric or NONEL
detonators:
 Higher timing precision (10 µs instead of 1-10 ms delay
scatter).
 Same high timing precision at long delay times (10 µs
at 5 second delays).
 Increased control over time delay
 Greater safety against accidental ignition (coded firing
signal).

17. Electronics Initiation Systems
 Current disadvantages include:
i. Higher price because of chip and capacitor cost
ii. Back to electric wiring – risk of ground faults or poor
contacts

18. Electronics Initiation Systems

19. Basic Detonator Construction

20. Wireless Electronic Blasting Systems
 Orica Mining Service’s Next Generation of Electronic
Blasting Systems is the culmination of 20 years of
laboratory testing and 15 years of in-field use.
 At the heart of their systems is the electronic timing
module.
 Offering up to 1000x greater accuracy and significantly
more timing flexibility than traditional pyrotechnics, it
provides greater control of energy.
 In the right hands, significant productivity gains are
possible through: fragmentation improvement,
muckpile shaping, vibration control, larger blasts,
improved wall/face conditions, and reduced overbreak,
damage and ground support.

21. Wireless Electronic Blasting Systems

22. Firing Methods
 Safety Fuse and Detonating Cord
 A safety fuse may be lit by using matches or, better,
special igniter torches. When several fuses are lit, a
control fuse, the length of which is 0.6 m shorter than
the shortest fuse of the round, may be lit and carried
around as an extra safety measure. When the control
fuse has burnt out, the blasting crew should evacuate the
blasting site immediately.

23. Firing Methods

24. Electric Firing
 The introduction of electric firing gave a higher degree
of safety for the people involved in blasting operations.
 The blaster became able to fire the blast from a
protected area and could have the moment of firing
completely under control.
 As it became possible to check with instruments that all
the detonators were connected, the risk of misfires
decreased.

25. Blasting Machine
 A blasting machine or shot exploder is a portable source
of electric current to reliably fire a blasting cap to trigger
a main explosive charge.
 It is mostly used in mining and demolition. The use of
the term "machine" dates from early designs that used
an electrical generator operated by winding a rotary
handle or pushing down a T-handle.
 Modern blasting machines are battery-powered and
operated by key switches and push-buttons, and do not
resemble the older designs.

26. Blasting Machine
 A typical "capacitive discharge" blasting machine works
by charging a capacitor from a battery, then discharging
the capacitor through an external circuit, called the
firing line, to fire the blasting cap.[1]
 While the machine is idle, an "internal shunt" is
connected across the output terminals so that any stray
voltages induced in the external circuit, for example by
nearby radio transmitters, are harmlessly short-circuited
without triggering the blasting cap.
 The machines also typically include an "abort" feature to
discharge the internal capacitor without firing the cap.

27. Blasting Machine

28. Blasting Machine

29. QUESTION TIME
???