Workbook 4 - Blasting Techniques

Introduction

Explosive Energy Production

When the explosives in a hole are detonated, three kinds of energy are produced:
- A. _______________
- B. _______________
- C. _______________
The shock waves which travel out away from the holes are called _______________ waves, and the waves which bounce back off the free face are called _______________ waves.
The upheaval of the rock is caused by high pressure and high temperature _______________ produced by the explosion which enter the cracks developed in the rock by the shock waves.
The amount of fragmentation desired depends upon (CHECK ANY CORRECT ANSWERS):
- A. Type of equipment being used to remove the overburden
- B. Size necessary for easy loading, especially if the product itself is being shot, and then loaded into trucks
- C. Type of strata
Inadequate stemming can result in airblast and flyrock.
- A. True
- B. False
Holes drilled off plumb or slanted will create (CHECK THE CORRECT ANSWER):
- A. No problem if the holes are deep enough
- B. Uneven burden or spacing and result in inefficient blasting
- C. A need for more explosives than usual

Answers - Page 1

Shock, heat, gases (IN ANY ORDER)
Compression, tensile (IN THIS ORDER)
Gases
A, B and C are all correct
A is correct
B is correct

Priming Fundamentals

The primer could be called the most important explosive in the hole since its job is to _______________ the main explosives charge.
Velocity is the rate at which the detonation front travels through the _______________.
ANFO must reach its steady state _______________ as rapidly as possible to assure a successful shot. Therefore, the type and amount (or size) of _______________ used is of the utmost importance when using ANFO.
Low-order detonation (can/cannot - which?) _______________ provide enough shock energy to properly detonate ANFO.
With high-order detonation, ANFO is detonated (CHECK THE CORRECT ANSWER):
- A. At a level very near its steady velocity
- B. Below its steady state velocity
- C. Above its steady state velocity

Answers - Priming Fundamentals

Detonate (OR SIMILAR ANSWER)
Column of explosives
Velocity, primer
Cannot
A is correct

Primer Placement

Better results are usually obtained with (CHECK THE CORRECT ANSWER):
- A. Several large primers in the bottom of the hole
- B. One primer of the proper size in the bottom of the hole
- C. Multiple primers throughout the hole
Certain primers (can/cannot - which?) _______________ be placed in water for short periods of time with little adverse effect.
In a wet hole, blasters often load wet-hole bags alternately with _______________.
Loading accuracy assures an efficient blast with minimum _______________.

Answers - Primer Placement

B is correct
Can
Primers
Flyrock

Delays and Decking Introduction

List three advantages resulting from delayed shots:
- A. _______________
- B. _______________
- C. _______________
A rule-of-thumb often used in delaying a shot is: One _______________ of burden for each one _______________ of delay.
List two reasons for decking:
- A. _______________
- B. _______________
When decking, proper loading practices and proper stemming (CHECK ANY CORRECT ANSWERS):
- A. Make for safer conditions
- B. Help protect all workers in the area
- C. Are required by law

Answers - Delays and Decking Introduction

Better fragmentation, less noise, less vibration (IN ANY ORDER)
Foot, millisecond
Reduce charge weight per delay, placement of charge where energy is needed (IN EITHER ORDER)
A & B are correct

Blasting Operation Safety Basics

Areas where charged holes await firing must be:
- A. Barricaded or _______________; and,
- B. Flagged or posted against _______________
Charged holes and detonating cord which are run over by equipment or vehicles could _______________ prematurely.
ANFO spillage should be (CHECK THE CORRECT ANSWER):
- A. Buried
- B. Burned
- C. Picked up and destroyed by approved method
Day boxes shall be constructed with a (wood/metal - which?) _______________ interior.
Personnel shall be cleared of the area prior to blasting and a warning device (shall/need not - which?) _______________ be sounded.
Crews can re-enter the blast area immediately after the blast.
- A. True
- B. False
Blasted areas (must/need not - which?) _______________ be inspected before the crews return to work.

Answers - Blasting Operation Safety Basics

A. Guarded; B. Unauthorized entry
Detonate
C is correct
Wood
Shall
B is correct
Must

Principles of Priming (Detailed)

Priming was discussed in depth in the film segment of this workbook, but this subject is so important that it warrants some review.

Wet Hole Considerations

First, the hole must be checked to make sure it hasn't filled with water. Even though primers are water-resistant, it's a good rule-of-thumb to (CHECK THE CORRECT ANSWER):

A. Load only dry holes
B. Shoot wet holes within 24 hours

Primer Sizing Rules

Another rule-of-thumb which pertains to the amount of primer to use when priming bulk ANFO:

The primer should be as deep (from the bottom of the hole to the top of the primer) as one-half the diameter of the hole.

So if the hole is 15 inches in diameter, the primer would be _______________ inches deep, or thick.

Key Points for Primer Diameter

The diameter of the primer should also be as close to the diameter of the hole as possible. This is often accomplished by pouring slurry around the primer to fill in the space between the primer and the hole.

Two points to remember:

A. Primer should be as deep as _______________ the diameter of the hole
B. The diameter of the primer should be as near the diameter of the hole as possible, even if the addition of _______________ is necessary to fill in the gap

Detonation Velocity

Primers are simply lowered into the borehole whether an electric, a non-electric, or a detonating cord system is used. It's essential that the priming is done properly to assure detonation of the explosive charge.

It is desirable that the column detonate at its maximum velocity, or at its _______________ velocity.

In other words, you must get the column detonating at its (maximum/minimum - which?) _______________ velocity as rapidly as possible.

Wet Hole Loading Technique

When a hole is loaded with bags of ANFO or other blasting agents, many blasters prefer to, especially in wet holes, load slurry and primer in the bottom and then alternate two bags of ANFO and primer.

PRIME EVERY TWO BAGS:
┌─────────────┐
│   ANFO BAG  │
├─────────────┤
│   ANFO BAG  │
├─────────────┤
│   PRIMER    │
├─────────────┤
│   ANFO BAG  │
├─────────────┤
│   ANFO BAG  │
├─────────────┤
│   PRIMER    │
├─────────────┤
│   SLURRY    │
└─────────────┘

Priming and loading in this manner assures detonation of the bags of blasting agent. The primer between the bags assures primer contact with every bag so that every bag will _______________.

Delays

Reasons for Using Delays

There are several reasons for the use of delays, such as (CHECK ONLY ONE ANSWER):

A. Reduced airblast and vibration
B. Improved fragmentation
C. Both of the above

Electric Blasting Cap Procedures

When using electric blasting caps, each cap would be checked for continuity with a blasting galvanometer before making up the primer. Then, as each cap is tied into the blasting circuit, it should again be tested with the _______________.

When tying-in electric caps, a twisted-loop tie should be used to join the wires and the connections (should/need not - which?) _______________ be kept clear of water or wet surfaces.

The completed cap circuit (CHECK THE CORRECT ANSWER):

A. Should be given a final blasting galvanometer check
B. Need not be checked again

Blasting Machine Limitations

Blasters should be aware that all blasting machines have limitations as to how many caps they will fire successfully. The information and directions accompanying the blasting machine should be studied carefully by the responsible person.

Non-Electrical Initiation Systems

If a non-electrical initiation system is used, only the gas detonating system (Hercudet is a major example) can be checked with instruments - gas pressure can be gauged to check continuity of the initiation circuit.

With all other non-electrical systems - detonating cord, Nonel, and cap-and-fuse - visual observation is the only way to check the initiation circuit.

Wiring Delay

Minimum Delay Requirements

When delays are used to control vibration, a delay of at least 8 milliseconds between their times of detonation is required, if each charge is to be considered a separate explosion.

This 8-ms delay requirement applies to shots in (CHECK ANY CORRECT ANSWERS):

A. The same hole
B. The same row of holes
C. Different rows

Decked Charges Definition

Decked charges can be defined as (CHECK THE CORRECT ANSWER):

A. Two or more explosive charges loaded into the bottom of a hole
B. A minimum of four charges in the same hole
C. A hole loaded with two or more individually primed charges

Vibration Control

When shots are fired in too short a time period, the vibrations they cause can add to each other, increasing the possibility of damage.

To help control vibration, whether the charges are in the same or different holes and/or rows, a delay of at least _______________ is required between charges.

Electrical Delay Systems

With electrical delayed blasting, the caps are all energized at the same time (unless a sequentially-timed machine is used), and misfires can be avoided more easily.

With electrical systems:

A. Unless a sequentially-timed blasting machine is used, the caps are all energized (at different times/simultaneously - which?) _______________
B. The delays are all (on the surface/in the hole - which?) _______________

Wiring Sequence

The first step in delaying (regardless of the system used) is to determine the desired firing time for each hole. This depends upon such factors as:

Where you want the shot ground to lie
Whether the holes are decked
Other site-specific factors

Once you know the firing time for each hole - in relation to the other holes in the shot - you're ready to select and "wire in" the appropriate _______________ to accomplish what you want.

Example: 10-Hole Shot with Electric Delays

Assume we have a 10-hole shot, with a delay time of 25 or more milliseconds between blasts. The holes are drilled in a square pattern, and we'll shoot them on the echelon using delay electric caps.

The numbers beside the holes indicate the delay periods - we'll use "0" instead of "1" for the first hole. Even though this is a square pattern, we intend to shoot it (down row/on the echelon - which?) _______________.

Using 25-ms delays with a 50-ms delay at hole 10:

Delay Pattern:
    Row 1    Row 2
    0  ←     2  ←
    ↓        ↓
    4  ←     6  ←
    ↓        ↓
    8  ←    10  ←

Fill in the firing times (ms):

Hole 0: 0 ms
Hole 2: ___ ms
Hole 4: ___ ms
Hole 6: ___ ms
Hole 8: ___ ms
Hole 10: ___ ms

Remember with electrical systems:

A. All of the caps are energized (WHEN?) _______________
B. The delay times, or periods, are controlled by the delay caps which are (on the ground/in the holes - which?) _______________

Sequentially-Timed Blasting Machines

Electrical blasting using a sequentially-timed blasting machine can become quite involved. A blasting machine might have as many as 10 circuits in it, and using these circuits in conjunction with caps which have a number of delay periods, you could wire and detonate a very intricate pattern.

For instance, the Atlas Rockmaster caps have as many as 38 periods. Using these and the 10 circuits available in the sequentially-timed blasting machine could enable you to expand to as many as _______________ periods between individual shots.

The combinations are (very limited/virtually unlimited - which?) _______________.

Gas Initiation Systems (Hercudet)

Gas initiation systems use all in-hole delays, providing the advantages of fewer cut-offs and misfires. Once the gas is ignited, it propagates through the circuit without stopping.

Key Fact: The gas in this system detonates at 8,000 feet per second. Therefore, it takes 1 millisecond for the gas to detonate through 8 feet of tubing.

Knowing this, you could create your own delay times by (CHECK THE LOGICAL ANSWER):

A. Wiring electrical caps into the system
B. Avoiding the use of gas systems
C. Simply adding lengths of tubing to the system

Example: If you're using Hercudet and have 25-ms delays in the holes, and you want to add 10 ms of delay between two holes, use an additional _______________ of tubing between those two holes.

Nonel and Detonating Cord Systems

These two systems have both in-the-hole and surface delays, and they can be used individually or in combination with each other. Both electrical caps and gas systems can be used in combination with detonating cord or Nonel systems.

Important: The surface delay used in Nonel or detonating cord systems will stop the detonation front for the time period stated by the delay. After that period, the detonation front will begin again.

When surface delays are used, the delay times must be (added together/subtracted from each other - which?) _______________ to determine the firing time of a given hole or charge.

Detonating Cord Example - In-Hole Delays Only

All of the delays are in the hole, and all are 25-ms delays. Since detonating cord shoots at 21,000 feet per second, if the delays are 25-ms, the three holes shown (CHECK THE CORRECT ANSWER):

A. Will fire at essentially the same time
B. Won't fire at all
C. Will fire at 25-ms intervals

Surface Delays Example

When only surface delays are used (no delays in the holes):

For hole #1:

A. The detonation stops at the first delay and waits (HOW LONG?) _______________
B. After this delay, the front moves on to both the primer in hole #___ and to the _______________ before hole #2 at the same time
C. The detonation front waits at this second _______________ for the indicated 9 ms, then moves simultaneously on to the _______________ in hole #2 and the delay for hole #3, etc.

Additive Delays

In the surface delays case, the delays are "additive":

Hole #1 fires after a 9-ms delay (9 ms after the detonation front reaches the delay)
Hole #2 fires at 18 ms after the first delay is reached
Hole #3 fires at ___ ms after the front reaches the first delay

Combined Surface and In-Hole Delays

When both surface and in-hole delays are used:

Hole #1 will fire after 34 ms (9 ms for the surface delay, plus 25 ms for the in-hole delay)
Hole #2 will fire at 43 ms (9 ms + 9 ms for the two surface delays, plus 25 ms for the delay in hole #2)
Hole #3 will fire at ___ ms

By using delays wisely - no matter what type of initiation system you're using - you can (CHECK THE CORRECT ANSWER):

A. Develop only a limited number of delay patterns
B. Probably work out most delay problems with little difficulty

Standard Nonel Delays

Standard, commonly used Nonel delays include: 17ms, 42ms, 100ms, etc. These are used in conjunction to attain the desired delay periods.

Example Pattern:

HIGHWALL
  |
  |  ●──────●──────●
  |  #1    #2     #3
  |
PIT SHOT GROUND

Hole #1 fires at 0 ms
Hole #2 fires at 17 ms (the shortest delay commonly used)
Hole #3 fires at ___ ms

Square Pattern on Echelon

Using 42ms delays in the first row and 17ms in the second row. The pattern is designed to move the overburden toward the shot ground.

Hole #1 fires at 0 ms
Hole #2 at 17 ms
Hole #3 at 42 ms

Complete the pattern using 17ms and 42ms delays for the remaining holes.

Delay Effectiveness

Since one millisecond equals one-thousandth of one second, an 8-millisecond delay between shots would not be noticeable to the naked eye or ear! However, this delay time has been proven effective in:

Reduction of noise and vibration
Obtaining the desired fragmentation

Delay Combinations

There are several combinations of surface delays which can be used, including:

9-ms, 17-ms, 25-ms, 42-ms, 100-ms, and 200-ms delays

The layout of the pattern, operator and blaster preference, and so forth, determine the surface delays to use. In addition, there are a number of in-hole delays that can be used.

The important thing to remember, regardless of the combination of delays used, is to hook up the shot so that there is never less than an ___ ms delay between charges.

Decked Charges

Definition and Purpose

Holes loaded with two or more individually primed and delayed charges which are separated by sufficient stemming to prevent cross-propagation are called decks.

Decking may be necessary due to:

Vibration problems
Strata which contain soft material which can blow out easily
Other site-specific conditions

In any case, each deck must be carefully separated with _______________.

Example: Square Pattern with Two Decks

Using an ignition system involving:

100-ms delays down row
17-ms delays across
175-ms and 200-ms delays in the holes

Primadet Delay Reference:

#	Delay Time
1	25 ms
2	50 ms
3	75 ms
4	100 ms
5	125 ms
6	150 ms
7	175 ms
8	200 ms

When the shots are fired, they must fire within the legal limits of the allowable minimum delay time. The only way to be sure is to calculate the sequence in which the shots will be fired in (CHECK THE CORRECT ANSWER):

A. Seconds
B. Microseconds
C. Milliseconds

Calculating Deck Firing Sequence

The first charge to be fired is considered Time "0".

In the example:

"0" would be shot first
Then 17-ms in Row 2
Then 17-ms in the third row

Indicate - in milliseconds - the times at which the shots will be fired:

A. 1st hole: ___
B. 2nd hole: ___
C. 3rd hole: ___

The first deck in Row 1 will detonate at 175 ms after Time "0". The first deck in the second row will fire 17 ms after the first deck in the first row, and so on.

Proper Loading Practices for Decking

A point to be emphasized concerning decking is the importance of proper loading practices.

Proper stemming must be maintained between the explosive decks. The exact amount is based on:

Explosive type
Borehole diameter
Other factors

This assures that one deck will not propagate to the next deck and helps prevent violation of the _______________ delay requirement.

Hole Loading Practices

Importance of Measurement

Many problems could be eliminated by constant measurement. Even though measuring every step of the loading procedure sounds painstaking and time-consuming, proper measurement could greatly enhance the safety and efficiency elements.

Question: How do you know the exact depth of the borehole unless you measure it?

Once the drill crew has measured and marked the hole and moved on to the next hole, there (is/is not - which?) _______________ the possibility of a cave-in or development of a wet hole.

So, the only way the blasting crew can know for sure that the hole has remained in the same condition as indicated by the driller is to _______________.

Explosive Loading Accuracy

Too much explosives (could/could not - which?) _______________ result in a blowout causing excessive airblast and flyrock.

The same holds true with the individual decks and the remaining area of the hole for proper stemming height. The only way you can be accurate in these procedures is to _______________ accurately.

Stemming and Fill Considerations

In some instances, the bench must be levelled out so fill is put in.

Fill Example:
┌────────────────────────┐
│        FILL (20')      │
├────────────────────────┤
│                        │
│   ORIGINAL CONTOUR     │
│                        │
│      HOLE DEPTH        │
│                        │
└────────────────────────┘

Good communications, including a driller's log, are necessary, since this may be the only way the blasting crew will know a situation such as fill exists.

Important: The loose fill which has been used to level out the bench should not be considered as part of the stemming or part of the total depth of the hole.

Therefore, when measuring hole depth or area of stemming, the measurement (CHECK THE CORRECT ANSWER):

A. Can include the 20' of fill shown in this drawing
B. Should include the fill as hole depth but not stemming
C. Must start with the original contour, excluding the fill entirely

In this particular case, if the fill were included in the hole depth and stemming, it would probably (CHECK THE CORRECT ANSWER):

A. Result in a blowout with increased noise and vibration
B. Not result in any noticeable side-effects because we're only talking about 20 feet

Blasting Operation Safety

Pre-Blast Requirements

Before the shots are fired (CHECK ANY CORRECT ANSWERS):

A. Warning sirens or horns must be sounded
B. Visual checks must be made
C. The area must be cleared to a safe radius from the blast

Personnel Training

Construction personnel should be carefully trained in the safety methods concerning blasting which are implemented in your mine operation.

Such personnel would include (CHECK THE CORRECT ANSWER):

A. Only blasters - those who load holes
B. Blasting foremen, not other blasting personnel
C. All employees working in and around a blasting area

Misfires

Prevention First

The simplest and safest method to deal with misfires would be to prevent them.

When all persons involved in the transportation, storing, handling, loading and firing of explosives follow the standards recommended by the governing bodies, the problem of misfires will be almost eliminated.

Misfires must always be considered as a possibility, and every misfire (is/is not - which?) _______________ a hazard.

Handling Misfired Explosives

With a misfire, the undetonated explosive is often thrown into a muck pile by the other holes. All visible explosives material should be removed, since digging with a shovel (could/could not - which?) _______________ result in detonation.

Repriming Options

When a misfired charge is found right after the blast, the stemming can often be washed out, the charge reprimed, restemmed and shot, but there will always be the danger of flyrock.

When the borehole has been disturbed or offset so that it's impossible to reopen the hole, the location should be marked. Then it may be possible to remove the explosives as the overburden is removed.

In any case, the procedures are quite hazardous and should be attempted only by (CHECK THE CORRECT ANSWER):

A. Trained and qualified personnel
B. Anyone who helps lay out the blast
C. The drilling crew

Drilling Near Misfires

Drilling near a misfired hole is extremely dangerous and should be avoided due to the fact that the misfired charge could have been disturbed or offset and drilling could result in _______________.

All misfires are hazardous. They should be dealt with only by qualified personnel - and in accordance with the procedures established by the explosives manufacturer.

Test - Workbook 4: Blasting Techniques

Instructions: Select the correct answer for each question.

1. Shock or compression waves travel:

A. Only the width of the drill hole
B. Straight up the drill hole
C. Away from the drill hole

2. The compression waves which bounce off the open face and return are called:

A. Ground tidal waves
B. Tsunami waves
C. Tensile waves

3. The amount of fragmentation desired depends upon the:

A. Type of equipment being used to remove the overburden
B. Type of strata
C. Both A and B are correct

4. The primer is used to:

A. Initiate the major explosive charge
B. Make certain the explosive is placed in the hole properly
C. Keep the explosive safe until detonation

5. Velocity is the rate at which the:

A. Column of explosives travels through the primer
B. Detonation front travels through the blasting pattern

6. The most widely used blasting agent in commercial mining is:

A. Water-gel slurry
B. Gelatinized dynamite
C. ANFO

7. Small primers which cause a burning action or low order detonation:

A. Move ANFO to its steady state velocity too quickly
B. Cannot provide enough shock energy to properly detonate ANFO
C. Produce carbon dioxide and cut off the oxygen supply for the detonation

8. When loading bulk ANFO, better results are usually obtained with:

A. Multiple small primers put on the cord and located throughout the hole
B. One primer of the correct size, in the bottom of the hole
C. One larger primer and several small primers placed throughout the hole

9. In wet hole loading, it's important to remember that primers must be kept out of the mud and in contact with the wet-hole bag to:

A. Obtain maximum efficiency and help prevent misfires
B. Keep from getting wet, or the charge will be non-existent
C. Make sure the explosive column is the right height

10. The use of bulk ANFO loading trucks is:

A. Not feasible for mining operations
B. Becoming more common in larger mining operations
C. Seldom used in mining operations

11. An advantage resulting from the delayed shots is:

A. More vibration
B. Less movement of the burden
C. Better fragmentation

12. Some good reasons for decking are:

A. Reducing explosives used in one period; placement of charge where energy is needed
B. Less fragmentation; more vibration
C. Both A and B are correct

13. All blasting will be performed under the direct control of an authorized person and will conform to all:

A. Demands of close residence owners
B. Federal and Provincial regulations
C. Preferences of the mine superintendent

14. Charged holes and detonating cord which are run over by equipment or vehicles could:

A. Detonate prematurely
B. Be crushed and necessitate reloading of the hole
C. Become completely useless and delay the shot

15. When personnel are cleared of the area prior to blasting, a warning device:

A. Need not be sounded
B. May or may not be sounded, depending upon Company rules
C. Must be sounded anyway

16. The primer should be as thick as:

A. Two times the diameter of the hole
B. The diameter of the hole
C. One-half the diameter of the hole

17. Whether an electric, a Nonel or a detonating cord system is used, primers are:

A. Simply lowered into the borehole
B. Wrapped with ANFO and dropped into the borehole
C. Simply dropped into the borehole

18. Before making up a primer, each electric blasting cap should be checked with a:

A. Voltmeter
B. Galvanometer
C. Oscilloscope

19. According to the rule of thumb, what is the minimum delay per charge?

A. 8-ms delay between shots in the same hole or row
B. 15-ms delay between shots in the same hole or row
C. 6-ms delay between shots in the same hole or row

20. Decked charges can be defined as:

A. A minimum of four charges in the same hole
B. A hole loaded with two or more individually primed or delayed charges
C. Two or more explosive charges loaded into the bottom of the hole

21. The construction personnel who should be carefully trained on blasting safety methods are:

A. Blasting crews only
B. Blasting foremen
C. All employees

22. Since misfires of blasting agents and detonating cord are not potentially as hazardous as dynamite misfires, they are considered:

A. A very minor problem
B. An extremely undesirable condition which must be taken seriously
C. A job slow-down instead of a potential hazard

Answer Key - Test

Question	Answer
1	C
2	C
3	C
4	A
5	B
6	C
7	B
8	B
9	A
10	B
11	C
12	A
13	B
14	A
15	C
16	C
17	A
18	B
19	A
20	B
21	C
22	B

Fill-in-the-Blank Answer Key

Introduction Section

Q1: Shock, heat, gases
Q2: Compression, tensile
Q3: Gases