Excavation Chapter 4
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An initiation system is a combination of ____ and ____ designed to ____ and ____ an explosive charge from a safe distance away.
The signal may either be ___ or ______
They provide a powerful localized shock or detonation to _____ explosives and primed blasting agents.
- explosive devices and component accessories
- transfer a signal
electric or non-electric
Electric initiation systems utilize an
electrical power source with associated circuit wiring to convey electrical energy to the detonators.
Non-electric initiation systems utilize
various types of chemical reactions ranging from deflagration to detonation as a means of conveying the impulse to non-electric detonators.
Electric Initiation Systems
Electric initiation system or blasting circuit consists of three basic elements:
- Electric detonators or electric blasting caps (EBC)
- Circuit wiring to connect the EBC to the power source
- Power source to provide electric energy to initiate the EBC.
Electric Blasting Caps (3)
- Instantaneous EBC
- Millisecond Delay EBC
Depending on the manufacturer, they are made in No. _ or No. _ strength.
They are designed for ____ initiation or for initiation within two _____ after current is applied.
No. 6 or No. 8 strength
Millisecond Delays EBC
Depending on the manufacturer, they are made in No. _ and No. _ strength
Delays range depending on manufacturers from __ms to ___ms.
They are used for construction, surface
mining, underground mining and tunneling operations.
No. 6 and No. 8 strength
8 ms to 3250 ms
Long Delays EBC
Depending on the manufacturer they can provide delays up to ____ sec.
The longer delays provide time for rock _____ under ____shooting conditions.
They are generally used in tunnel and drift driving, shaft sinking, raise blasting and in underground mining.
Electric Initiation Circuits
There are three types of electric initiation circuits:
- Single-Series circuits - for relatively small numbers of EBC
- Parallel circuits - generally for underground blasting
- Parallel-Series circuits - for large numbers of EBC
Circuit Wiring: types of wires used (4)
Legwires: insulated wires extending from EBC
Connecting wires: insulated wire connecting legwire to firing line, connect between blastholes or individual series to lead line (16 to 20 gauge).
Firing line or lead line: used to connect the power source to the detonator circuit. Tough waterproof insulated 10 to 14 gauge solid copper wire, may be duplex.
Buswire: 10 to 14 gauge, solid copper wire for connecting series-in-parallel and parallel circuits. Reverse hookup Is recommended.
- Vo- I1R1....-InRn = 0
- Io-I1-In = 0
Resistance of Circuits (2)
All EBC are connected in a line where the current has ___ path to follow with the ___amount of current.
Minimum recommended current is ___ amps DC or __ amps AC.
Maximum number of EBC in a single series should not exceed __ and/or __ ohms
- only one, same
- 1.5 amps DC or 2.0 amps AC
- 50 and/or 100
Mostly used with _____ line ( and with some capacitor discharge blasting machines) for large number of EBC.
Minimum recommended current is __ amps DC or AC/caps.
Maximum current must not exceed __ amps/cap to prevent ___.
- power line
This type of circuit is used when the number of EBC exceed __.
Each individual series should not have more than __ EBC and/or a maximum resistance of ___ ohms.
The resistance of each series must be ___ to have the current divided evenly in each series (series balancing).
Reverse hookup is also recommended. The minimum current required for each series is __ amps DC or __ amps AC.
- 40, 100
- the same
- 1.5 amps DC or 2.0 amps AC
Optimum Number of Series in Parallel -Series Circuit
Power Source for EBC
______ or _____
—_____ type (____)
— ___-____ type
____ of ____
______ ____ of _____
- Blasting Machines or Exploders
- — Generator type (twist)
- — Condenser-Discharge type
- dry cell battery
- bank of condensers
- exponential decay of current
Power Line Blasting
Hazardous Extraneous Electricity
Stray ground current from poorly grounded electrical equipment.
Lightning and static electricity from electrical storms, danger is Increased in presence of power lines, water lines, fences or other conductors near by.
High frequency energy from radio transmitters.
Induced currents from high voltage transmission lines, alternating electromagnetic fields.
Static electricity generated by wind and snow storm (especially at low humidity), conveyor belts, pneumatic conveying of ANFO.
Galvanic currents generated by dissimilar metals.
Non-Electric Initiation Systems
Non-electric initiation systems are used as an alternative to electric initiation systems in all situations except underground coal or other gassy mines.
These systems cannot be initiated by stray currents, static electricity or high-frequency radio signals.
These systems include but not limited to: (3)
- Safety fuse and caps
- Detonating cord-MS connector-Blasting caps
- Shock Tube-Blasting caps
Still in use but not recommended for production blasting
Consists of black powder incased in a flexible, water-proofed textile wrapping.
Its burning rate is controlled by powder composition, with a typical average burning rate of 45 sec/ft.
From the point of ignition the flame is conveyed to a heat sensitive cap.
Detonating cord-MS connector-Blasting caps
Detonation cord is a round, flexible cord containing a center core of high explosive, usually PETN (pentaerythiritol tetranitrate), within a reinforced waterproofing covering.
Detonating cord is relatively insensitive and requires a proper detonator such as No. 6 strength cap, for initiation.
Detonating cords have a detonation velocity of 22,000 ft/sec.
The cord's detonation wave will initiate cap sensitive high explosives (primer), adjoining detonating cord, and non-electric delay caps.
Detonating cord core loads range from 2.5 grains/ft to 800 grains/ft (1lb = 7000 grains).
Most detonating cords of 18 grains or higher have self-to-self reliability defined as being able to Initiate themselves.
Detonating cords with a charge of less then 18 grains/ft must be initiated by a higher grain detonating cord (25 grains) or by a # 6 or higher strength blasting cap.
Detonating cords used to initiate high explosive down the borehole are called downline.
Downlines are connected to Detonating cords at the surface, called trunklines.
MS connectors are used as delay in Detonating Cord circuit for hole to hole and row to row delays.
They are non-electric initiation systems in which the ignition charge in each individual cap is activated by a firing signal traveling through a tube containing a reactive material coating, consisting of a mixture of HMX and aluminum.
They can readily be initiated by conventional detonating cord, an electric or non-electric detonator or one of the various mechanical short shell starter device.
When initiated, the reaction travels at about 6500ft/sec. The signal is strong enough to propagate through most sharp bends, kinks and knots.
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