Workbook 6 - Special Problems

Introduction

Our primary purpose is to make you aware of some of the problems which do exist, how to avoid them, and how to deal with them when they occur. Job knowledge, sound judgment and common sense will go a long way toward reducing problems. And when the number of problems is reduced, there will also be a reduction in accidents.

Preliminary Questions

Responsibility and Definitions

The prevention of special problems in the blasting area are the responsibility of:
- A. Drilling crews
- B. Blasters
- C. Everyone involved - from the initial planning through the shot firing
The best definition of burden is the distance:
- A. Between holes in a row
- B. From the face to the first row of holes, and the distance between rows
- C. From loaded holes to unloaded holes
Spacing is defined as the distance between _______________.
Excessive burden can result in blowouts and flyrock.
- A. True
- B. False
When blowouts occur, fragmentation (may be poor/is unaffected - which?) _______________.
Excessive burden can cause too (little/much - which?) _______________ fragmentation of the toe in front of the holes.
Noise and vibration which exceed allowable limits can be caused by too much _______________.

Answers - Page 1

C is correct
B is correct
Holes in a row
A is correct
May be poor
Little
Burden

Spacing and Priming Issues

Poor fragmentation and toe-in between the holes are problems common to:
- A. Too little burden
- B. Too much spacing
- C. Excessive priming
Excessive noise and vibration can be caused by too much burden.
- A. True
- B. False
Insufficient priming can result in (CHECK ANY CORRECT ANSWERS):
- A. Increased coal production
- B. Poor fragmentation
- C. Fewer complaints
- D. Inefficiency
The purpose of the primer is to detonate the _______________.
Insufficient priming (can/cannot - which?) _______________ cause unsuccessful shots.

Answers - Spacing and Priming

B is correct
A is correct
B and D are correct
Blasting agent
Can

Pattern Accuracy

Excessive burden is often the result of (CHECK ANY CORRECT ANSWERS):
- A. Incorrect figures
- B. Incorrect measurements
- C. Stepping off
Throwing the pattern off by even a few feet (CHECK THE CORRECT ANSWER):
- A. Can cause no problem
- B. Is the accepted practice
- C. Can result in an unsuccessful shot
Good communications between crews and between workers play an important role in successful blasting.
- A. True
- B. False

Answers - Pattern Accuracy

A, B and C are all correct
C is correct
A is correct

Stemming and Wet Holes

In determining the amount of stemming the measurement should (CHECK ANY CORRECT ANSWERS):
- A. Include the depth of backfill
- B. Be the distance between the bottom of the borehole and the original contour
- C. Never include the depth of backfill
When bulk-loaded ANFO is used as the main explosive charge, special handling of wet holes is not necessary.
- A. True
- B. False
Some companies are using a plastic liner in the hole to keep explosives (dry/tightly packed - which?) _______________.
The best way to deal with problems is to (CHECK THE CORRECT ANSWER):
- A. Prevent them whenever possible
- B. Put additional workers on the job
- C. Reduce the work load

Answers - Stemming and Wet Holes

B and C are correct
B is correct
Dry
A is correct

Special Problems - Detailed

General: Excessive Burden

Excessive burden can cause (CHECK ANY CORRECT ANSWERS):

A. Blowouts and flyrock
B. Excessive fragmentation
C. Noise and vibration
D. Toe problems
E. Poor fragmentation

Burden Definition Review

Burden is the distance from the _______________ to the first row of holes... and the distance between _______________.

Rule-of-Thumb: Burden Calculation

Accuracy in all steps of the blasting operation is essential to a successful shot. Here is the rule-of-thumb to follow:

Burden = Borehole diameter (thought of as feet instead of inches) × 2

So, if you have a 7-inch borehole, the burden would be (7/14/28 - which?) _______________ feet.

Examples with common-sized boreholes:

A. 10-5/8" borehole equals approximately ___ feet of burden
B. 15" borehole equals ___ feet
C. 12" borehole equals ___ feet of burden

Pattern Layout

Correctly laid out pattern:

  ●     ●     ●     ●     ●
  14'   14'   14'   14'
  ●     ●     ●     ●     ●
  14'   14'   14'   14'
  ●     ●     ●     ●     ●

Notice how the 14' burden has been carried on throughout the entire pattern.

Carelessly laid out pattern:

  ●     ●     ●        ●      ●
  14'   10'   20'   8'
  ●         ●   ●    ●     ●
  18'   6'    22'  12'
  ●     ●         ●        ●      ●

Which pattern would produce the most successful shot, with fewer problems?

Answer: _______________

Most problems (can/cannot - which?) _______________ be avoided.

Pattern Error Example

Assume that the hole size is 7" and that the planned burden is therefore 14 feet. Somehow, perhaps by inaccurate measurements, the burden in the last row is _______________ feet more than initially planned.

Since the powder factor is pre-determined, the holes in the last row will be loaded with the same amount of explosives as the holes in the first row.

Will the fragmentation resulting from the shots in the second, third and fourth rows of holes be the same as that attained by the holes in the first row? (YES or NO) _______________

WHY? _______________

Conditions from Off-Pattern Drilling

List the conditions which could develop from too little or excessive burden due to getting off pattern:

A. _______________
B. _______________
C. _______________
D. _______________

Too Little Burden

When too little burden exists, there can be a great deal of airblast and flyrock. In other words, excessive _______________ can occur when the burden is too small.

There may also be too much fragmentation with too little burden:

A. When the bench is too greatly _______________, the dragline may not be able to rest safely on it
B. With a shovel working in the pit, too little burden may result in throwing too much _______________ into the pit - and could result in hazardous conditions, since the _______________ could crumble and fall as it's removed

While parts of the bench can be overly fragmented when too little burden exists, much of the explosive force can often escape in the form of airblast.

Burden Summary

Problems can result (CHECK THE CORRECT ANSWER):

A. Only when there's too much burden
B. Only when there's too little burden
C. When there's too much or too little burden

Spacing

Definition and Calculation

Too much spacing can result in several problems similar to those caused by excessive burden:

Poor fragmentation
Toe-in between the holes
Noise and vibration

Definition: Spacing is simply the distance between _______________ in a _______________.

Rule-of-Thumb:

Spacing = 1.5 × Burden

Examples:

With a 7" borehole: burden = ___ feet, spacing = ___ feet
With a 12" borehole: burden = ___ feet, spacing = ___ feet

Summary of Rules

Calculation	Formula
Burden	_______________ × 2
Spacing	_______________ × Burden

Practice: Layout Pattern

In the space below, lay out a pattern using a 16" diameter hole:

Burden = ___ feet
Spacing = ___ feet

Excessive Spacing Consequences

Considering the discussion of excessive burden, what could happen as a result of too much spacing?

Answer: _______________

Borehole Measurement

Importance of Verification

We've mentioned the importance of accurate measurement for burden and spacing - we should also stress the importance of measuring the borehole itself.

Scenario: The borehole when the driller's crew finished:

Depth: 55 feet

Later: How the borehole looked by the time the hole was loaded:

Cave-in: 10 feet of fill at bottom
Actual available depth: 45 feet

This situation would affect the amount of explosives because the powder factor was calculated on ___ feet of borehole, where in fact, there is now only ___ feet.

This (could/could not - which?) _______________ result in blowouts and toe problems due to the now insufficient amount of stemming, because the explosive is too high in the hole.

Detection of Cave-ins

The fill or the cave-in in the bottom of the hole could have been detected and the problem eliminated by (CHECK THE CORRECT ANSWER):

A. Visually inspecting the hole
B. Measuring the hole before loading

Remedying Backfill

When a backfill situation is discovered, the situation must be remedied before the hole is loaded. The only logical step is to (CHECK THE CORRECT ANSWER):

A. Ignore the situation and load the hole as planned
B. Bring the drill back to the hole and re-drill it
C. Adjust the amount of explosives in the hole to allow for the backfill

Most problems - like most accidents - (can/cannot - which?) _______________ be prevented.

Rider Vein

Definition

Sometimes, there's a smaller vein of coal - one which is so thin that it's not worth mining - through the overburden over the main vein.

Cross-Section View:
┌─────────────────────────────┐
│        OVERBURDEN           │
├─────────────────────────────┤
│        RIDER VEIN           │  ← Smaller, thin vein
├─────────────────────────────┤
│    PARTING (Overburden)     │
├─────────────────────────────┤
│        MAIN VEIN            │  ← Main coal seam
└─────────────────────────────┘

The smaller vein is referred to as a _______________ vein, and (ANFO/stemming - which?) _______________ is placed in the hole where this vein is located.

Preventing Energy Escape

The top overburden layer could be shot (if necessary) and the rider vein mined, then the second layer of overburden (parting) could be shot and removed. But when a rider vein is to be shot with the overburden, it could provide an "escape route" for the energy of the blast.

To prevent this:

A. _______________ is placed in a hole at the location of the _______________
B. Above this point, another _______________ and more _______________, up to the remainder of the stemming, are loaded into the hole
C. By doing this, the overburden is fragmented by (more/less - which?) _______________ of the energy than would otherwise be available

So, when the second vein (rider vein) is of no value, stemming is used to help obtain maximum _______________ from the explosives in the hole.

Wet Holes

Pre-Loading Inspection

The borehole must be inspected before loading to make certain it is the correct _______________ for the planned amount of explosives.

However, this is not the only reason for hole inspection. The blaster's crew should always check to determine:

Whether there are obstructions, such as rocks or mud-squeezes in the column
Whether there is water in the bottom

Logically, such conditions (CHECK THE CORRECT ANSWER):

A. Need not be considered when loading the hole
B. Require special handling and techniques for hole loading
C. Point out the need for extra caution, but the loading procedure is the same as for dry holes

Handling Obstructions

When there's an obstruction in the hole - mud or a rock has protruded into it, partially or completely blocking it - you should handle the situation as you would in a cave-in:

Bring the _______________ back and _______________ the hole.

Wet Hole Loading Procedures

After the hole is measured, usually the first step in hole loading is the lowering of the properly assembled (explosive/primer - which?) _______________ to the bottom of the hole.

When a hole is wet and ANFO wet-hole bags are to be used, a detonating cord downline is attached to the primer. The cord is then used as a stringer for extra primers loaded alternately with the wet-hole bags.

In this instance (CHECK THE CORRECT ANSWER):

A. All of the wet-hole bags are placed in the bottom of the hole, and the primers positioned on top of the bags
B. All priming material is put on the bottom of the hole - then the wet-hole bags
C. The hole is loaded alternately with primer and wet-hole bags

Alternate Loading Method

Many blasters prefer to load wet holes in this manner:

Wet-hole bags in hole first
Then primer
Two wet-hole bags next
And so forth

This assures primer/explosive _______________.

Bulk ANFO Loading

When bulk ANFO is used, it is poured to the correct height of the predetermined powder column. A probe pole or weighted tape to gauge the correct height is very important since:

The location of a powder column can change if the bottom has caved in
The proper amount of powder is essential
Sufficient stemming is important to a successful shot and the minimizing of _______________

Loading Through Water

In wet holes, slurry or wet-hole bag ANFO is loaded to (CHECK THE CORRECT ANSWER):

A. Form a solid base for ANFO
B. Build up out of the water
C. Boost the primer since these products are completely waterproof

Almost Full of Water

Occasionally you might come across a hole that is almost full of water. When this happens, you must remember the slow sink rate of slurry and ANFO wet-hole bags.

When loading under these conditions you should (CHECK THE CORRECT ANSWER):

A. Allow enough time between drops for the bags to sink so they won't jam up the hole
B. Skip this hole because you cannot shoot it
C. Drop the bags quickly so the weight will force them to the bottom

The situation described above points out another instance where accurate measurements are a must to determine whether the hole is loaded properly.

A. True
B. False

Misfires

Post-Blast Safety

A misfire is a condition which must be handled with the utmost caution for the safety of all workers.

After the blast, never return to the blasted area until enough time has passed to allow smoke, dust and fumes to clear away.

Returning to a blast area too soon after the shot is fired could (CHECK ANY CORRECT ANSWERS):

A. Result in accidents caused by poor visibility
B. Be hazardous if there happened to be undetonated explosives remaining in the area

Burning Charges

A misfired charge that is burning is extremely hazardous because it could _______________.

Pre-Return Checks

The blast area should be checked before the workers return to the site. So, it makes sense to:

A. Wait until the blast area has cleared of _______________ and _______________
B. Never return to a blasting site until it has been _______________ by the blaster in charge

Prevention

It has been determined that if all recommended procedures for the transportation, storing, handling, loading, and firing of explosives were strictly followed, the problem of misfires would be practically eliminated.

If all jobs were performed properly, most misfires could be _______________.

But we said most misfires could be prevented, not that the chances of a misfire have been eliminated.

A misfire (CHECK THE CORRECT ANSWER):

A. Is a very hazardous situation
B. Is no longer a threat in the coal mining industry
C. Need not be considered dangerous enough for special precautions

Because of the possibility of serious accidents and injuries caused by misfires, everything possible must be done to _______________ them.

Legal Requirements

When a misfire is discovered:

First action: Report it to the proper supervisor

The misfire must be disposed of safely (CHECK THE CORRECT ANSWER):

A. While work is being performed in the area
B. Before any other work is done in the blasting area
C. In conjunction with overburden removal carried out with added precautions

Wait Times

When EB caps have been used, workers should wait for at least ___ minutes before returning to the blast site.

Sometimes companies have rules which are even more stringent than Provincial law, but in any case, the law requires workers to stay away from the blast sites for at least ___ minutes when EB caps have been used and a misfire is suspected.

When explosives are suspected of burning in a hole:

All persons in that area must be removed to a safe location
No one should return to the area until the danger has passed
Never return within ___ hour(s)

The law also requires that all blast sites be examined for undetonated explosives after each blast and that all discovered undetonated explosives shall be disposed of safely.

Summary of Legal Requirements

According to the law:

A. Misfires shall be reported to the proper _______________
B. Workers shall not return to the blast site for ___ minutes when _______________ have been used
C. When explosives are suspected of burning in a hole, workers should never return within _______________
D. Blasted areas shall be examined for undetonated explosives (WHEN?) _______________

Handling Procedures

A misfired charge is very hazardous, and they must all be disposed of by _______________ persons.

In the event of a misfire, a considerable amount of the explosives load will probably be thrown into the muck pile by the action of the other holes.

All visible explosives should be cleaned up because the operation of the shovel or other removal equipment could cause them to _______________.

When a detonator is included in the unfired explosives, the seriousness of the situation is greatly (increased/decreased - which?) _______________.

Disposal Methods

Once the shovel digs through the pile, the remains of the misfired hole will often be exposed.

Two common practices used to dispose of misfires:

A. Desensitize with _______________
B. Reprime and _______________ the explosives

Refiring Options

If a misfired charge is discovered and the problem is easily seen (an above-ground break in the initiation system, for example), and it would be safe to refire the hole, you can simply reconnect the system and refire that hole.

But if the problem is down-hole, it may be necessary to:

Remove the stemming, and perhaps even the explosives, by washing (with water) or blowing (with air) the hole clear
Reprime the hole
Reload if necessary
Restem
After appropriate safety precautions are taken, _______________

Hole Cannot Be Reopened

If the hole is offset or disturbed in a manner that prevents it from being reopened, the location should be marked so the _______________ can be recovered as the overburden is removed.

Summary of Misfire Handling

Refiring or recovery of undetonated explosives is the preferred mode of action. These two methods are usually carried out after making these considerations:

A. When a misfire is found right after the blast, the safest thing to do is _______________ the _______________ and _______________ the charge, or _______________ the explosives
B. If a hole cannot be reopened, the location of the misfire should be _______________ so the explosives can be recovered or disposed of when the overburden is removed

Flyrock Danger

It is often extremely dangerous to refire undetonated explosives, even when the stemming can be removed and the charges reprimed. The problem is that the other holes in the shot will have dislodged the burden in front of this hole.

This situation (could/could not - which?) _______________ result in a flyrock problem.

Therefore, it makes sense to (CHECK THE CORRECT ANSWER):

A. Go ahead and refire the undetonated charges
B. Seek expert advice from the explosive manufacturer before taking any action

Final Reminders

The very nature of explosives demands respect from those who handle or work in close proximity to explosives. Common sense and good judgment can and do prevent accidents.

For your own well-being - and the well-being of your co-workers:

Know your job
Don't take any chances
If you have any doubts about how to handle a specific problem - find out the proper method before you take any action
Above all, observe any Federal and Provincial safety regulations - and those of your Company

Test - Workbook 6: Special Problems

Instructions: Select the correct answer for each question.

1. Prevention of special problems in the blasting area is the responsibility of:

A. Drilling crews
B. Blasters
C. Everyone involved - from the initial planning through the shot firing

2. Burden is the distance:

A. Between holes in a row
B. From the face to the first row of holes - and the distance between rows
C. From loaded holes to unloaded holes

3. Spacing is the distance:

A. From the face to the first row of holes, and the distance between rows
B. Between holes in a row
C. From loaded holes to unloaded holes

4. Too much burden and/or too much spacing can result in:

A. Blowouts and flyrock
B. Too little fragmentation of the toe in front of the holes
C. Both A and B are correct

5. Poor fragmentation and toe-in between the holes are problems common to:

A. Too little burden
B. Too much spacing
C. Excessive priming

6. Insufficient priming can result in:

A. Increased coal production
B. Fewer complaints about noise and vibration
C. Ineffective priming

7. The purpose of the primer is to detonate the:

A. Blasting agent
B. EB cap
C. Detonating cord

8. When a borehole is filled with stemming which is too loose or too porous, the force of the blast will:

A. Cause too much fragmentation
B. Cause a blowout
C. Prevent detonation of the explosives

9. Excessive burden is often the result of:

A. Incorrect figuring
B. Incorrect measurements
C. Both A and B are correct

10. Throwing the pattern off a few feet:

A. Usually causes no problem
B. Is an accepted practice
C. Can result in an unsuccessful shot

11. Due to the special primers and blasting agents used, special handling of wet holes is:

A. Not necessary
B. Necessary
C. Necessary only if deemed so by the blasting crew

12. The best way to deal with special problems is to:

A. Prevent them whenever possible
B. Put additional workers on the job
C. Reduce the work load

13. When laying out a blasting pattern the rule-of-thumb is burden equals the borehole diameter (in feet) times:

A. Three
B. Two
C. Four

14. When laying out a blasting pattern, if you have a seven-inch borehole the burden would be:

A. 14 feet
B. 7 feet
C. 28 feet

15. Spacing of staggered pattern is calculated by using this rule-of-thumb - spacing equals:

A. 3 times burden (3 × B)
B. 1.5 times burden (1.5 × B)
C. 2.5 times burden (2.5 × B)

16. When using the above calculation for spacing, a borehole with a 12-inch diameter would have spacing of:

A. 36 feet
B. 24 feet
C. 18 feet

17. Boreholes must be inspected before loading to check for any obstructions in the column and whether there is water in the bottom. Logically, such conditions:

A. Need not be considered when loading the holes
B. Require special handling and techniques for hole loading
C. Point out the need for extra caution, but the loading procedure is the same as for dry holes

18. Once a containment is covered, usually the first step in hole loading is the lowering of the properly assembled:

A. Explosive to the bottom of the hole
B. Primer to the bottom of the hole
C. Slurry and blasting cap into the hole

19. When a hole is wet and NCN wet-hole bags are to be used, the hole is loaded:

A. With all of the wet-hole bags in the bottom of the hole and the primers positioned on top of the bags
B. With all priming material on the bottom of the hole then the wet-hole bags
C. Alternately with primer and wet-hole bags

20. In wet holes, cartridged slurry or wet-hole bags may be loaded to:

A. Form a solid base for ANFO
B. Build up out of water
C. Boost the primer, since these products are completely waterproof

21. Occasionally a hole might be almost full of water - when this happens, the loader must:

A. Allow enough time between drops for the slow sink rate of slurry and NCN wet-hole bags
B. Skip this hole because it cannot be shot
C. Drop the bags quickly so the weight will force them to the bottom

22. Rushing back into a blast area immediately after the shot is fired could:

A. Result in accidents caused by poor visibility
B. Be hazardous if there happened to be undetonated explosives remaining in the area
C. Both A and B are correct

23. Wait until a blast area has been cleared of smoke, dust, and fumes before:

A. Inspecting the area for possible problems
B. Calling in the dragline
C. Drilling another hole

24. All misfires are:

A. Potential accidents
B. No longer threats in the coal mining industry
C. Not considered dangerous enough for special precautions

25. Misfires shall be disposed of safely:

A. While work is being performed in the area
B. Before any other work is done in the blasting area
C. In conjunction with overburden removal which is carried out with added precautions

26. The law states that when EB caps have been used, workers should wait at least:

A. 15 minutes before returning to the misfired hole
B. One hour before returning to the misfired hole
C. 30 minutes before returning to the misfired hole

27. The law requires workers to stay away from explosives burning in a hole for at least:

A. 15 minutes
B. 1 hour
C. 30 minutes

28. The law requires that all blasted areas be examined for undetonated explosives:

A. Every shift change
B. After each blast
C. At least one time each day

29. A common practice used to dispose of in-hole misfires is:

A. Repriming the charge and firing the explosives
B. Reshooting the original charge without additional priming
C. Covering the misfired shot with at least 10 feet of dirt

Answer Key - Test

Question	Answer
1	C
2	B
3	B
4	C
5	B
6	C
7	A
8	B
9	C
10	C
11	B
12	A
13	B
14	A
15	B
16	B
17	B
18	B
19	C
20	B
21	A
22	C
23	A
24	A
25	B
26	A
27	B
28	B
29	A

Fill-in-the-Blank Answer Key