Drilling-And-Blasting
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DRILLING AND BLASTING IN MINING – COMPLETE GUIDE (2026)

ByMine Mitra

Drilling and blasting form the backbone of modern mining. Whether it’s a large opencast metal mine, a limestone quarry, a coal overburden operation, or an underground hard-rock mine, almost every ton of rock produced today is broken using drilling and blasting.

What is Drilling and Blasting in Mining?

Drilling & Blasting is a mechanical + explosive process used to break rock into a workable size.

The sequence is simple:

  1. Drill holes in the rock
  2. Fill them with explosives
  3. Initiate them safely
  4. The blast fractures the rock
  5. Load → Haul → Crush → Process

Mining without drilling and blasting is impossible in hard rock. Even in soft rock, drilling & blasting reduces cost and improves fragmentation.

Importance of Drilling & Blasting

Mining productivity depends directly on drill & blast quality:

  • Better fragmentation → faster loading
  • Less oversized → better productivity
  • Controlled vibration → safer blasting
  • Correct drilling → reduced explosive consumption
  • Proper spacing → uniform breakage
  • Ideal burden → safe energy release

Even a small drilling error can destroy an entire blast pattern.

Drilling And Mining In Mining

Types of Drilling Used in Mining

A) Rotary Drilling

Uses rotation to cut rock.
Used in:

  • Large opencast metal mines
  • Soft formations
  • 150–350 mm holes

Advantages:

  • High rate of penetration
  • Very large diameter holes

B) Percussive Drilling (Hammering Action)

This type breaks rock by repeated hammering.

Types:

  1. Top Hammer (TH)
    • Good for short holes
    • Used in small quarries
  2. Down-The-Hole (DTH)
    • Hammer is directly behind bit
    • Deep, straight holes
    • Most popular in limestone & stone quarries

Why DTH is important?

✔ Minimal deviation
✔ High accuracy
✔ Uniform fragmentation

C) Jumbo Drilling (Underground)

Used for tunneling & development headings.
Comes with 1–3 booms, allowing multiple holes in one setup.

Applications:

  • Drivage
  • Shaft sinking
  • Long-hole blasting
  • Production stoping

Key Drilling Parameters (Exam + Field)

ParameterMeaning
Burden (B)Free face se first hole tak distance
Spacing (S)Hole-to-hole distance
Bench Height (H)Floor to free face height
Sub-DrillingExtra depth for full toe breakage
StemmingInert material above explosive column
Charge per HolePQ × Density × Hole Volume

Typical Ratios

  • Spacing = 1.2–1.5 × Burden
  • Stemming = 0.7 × Burden
  • Sub-drilling = 10–30% of hole depth

Explosives Used in Mining

1. ANFO (Ammonium Nitrate + Fuel Oil)

  • Most common
  • Cheap
  • Easy to load
  • Not water-resistant

Used in:

  • Dry holes
  • Bulk blasting
  • Surface mines

2. Slurry Explosives

  • Water-resistant
  • Good for wet holes

3. Emulsion Explosives

  • High velocity of detonation (VOD)
  • Best for hard rock
  • Very good water resistance

Used in:

  • Granite mines
  • Metal mines
  • Underground charging

4. Cartridge Explosives

  • Gelatin / permitted explosives
  • Underground fiery mines
  • Small diameter holes

Initiation Systems

A) Detonators

  • Electric
  • Non-electric (NONEL) → industry standard

B) Detonating Cord (Det Cord)

Used for surface connections.

C) Delay Systems

  • Short delay
  • Long delay
  • Electronic delay → highest accuracy

Delays help in:
✔ Fragmentation
✔ Vibration control
✔ Reducing flyrock

Blasting Patterns

Surface Mines

  • Square
  • Staggered (most efficient)
  • Line drilling
  • Pre-splitting
  • Buffer blasting

Underground Mines

  • Burn Cut
  • V-Cut
  • Fan Cut
  • Pyramid Cut
  • Parallel Cut

Blasting Problems & Their Solutions

ProblemCauseSolution
FlyrockOverchargingReduce charge, increase stemming
OverbreakExcess energyControlled delay & charge
High vibrationLarge MICReduce charge per delay
Air blastBad stemmingUse proper stemming material
MisfiresPoor connectionProper testing & DGMS checklist

Important Formulas (Exam Use)

Powder Factor (PF):

PF = Rock broken (tons) / Explosive used (kg)

MIC (Maximum Instantaneous Charge):

MIC = Charge fired in one delay

Stemming Length:

≈ 0.7 × Burden

Sub-drilling:

≈ 0.2 × Hole depth

Conclusion

Drilling and blasting are the heart of mining operations.
Performance of the entire mine — from loading to hauling to crushing — depends on how well the drilling & blasting is done. This is article uses for the exam of Mine Supervisor and Royalty Inspector for mining and geology aspirant.

A drilling mistake = a blasting disaster.
A blasting mistake = a production disaster.

MineMitra – MCQ Test (150 Questions)

MineMitra – 150 MCQs

1. Drilling in mining is primarily used for:

  1. Creating ventilation
  2. Making blast holes to place explosives
  3. Measuring rock density
  4. Groundwater extraction
Correct: b
Drilling creates blast holes to charge explosives.

2. The distance between a blast hole and nearest free face is called:

  1. Spacing
  2. Stemming
  3. Burden
  4. Sub-drilling
Correct: c
Burden controls the direction of rock movement.

3. Spacing refers to:

  1. Distance between adjacent holes
  2. Bench height
  3. Charge length
  4. Drill rod length
Correct: a
Spacing affects fragmentation distribution.

4. ANFO consists of ammonium nitrate and:

  1. Diesel
  2. Kerosene
  3. Fuel Oil
  4. Emulsion
Correct: c
ANFO = Ammonium Nitrate + Fuel Oil.

5. The most common drilling method in limestone quarries:

  1. Rotary
  2. Top Hammer
  3. DTH drilling
  4. Hand drilling
Correct: c
DTH gives straight, deep, accurate holes.

6. Stemming is placed to:

  1. Increase hole depth
  2. Confine gases inside the hole
  3. Increase burden
  4. Reduce spacing
Correct: b
Stemming prevents gas escape and reduces flyrock.

7. In DTH drilling, the hammer is located:

  1. At surface
  2. Halfway down drill pipe
  3. Just behind the drill bit
  4. Inside compressor
Correct: c
Closer hammer → better energy transfer.

8. Best explosive for wet holes:

  1. ANFO
  2. Black Powder
  3. Slurry/Emulsion
  4. Detonating Cord
Correct: c
Slurry/emulsion explosives are water-resistant.

9. Powder Factor is:

  1. kg of explosive per ton of rock
  2. Tons of rock broken per kg of explosive
  3. Hole depth × diameter
  4. Delay interval
Correct: b
PF represents blasting efficiency.

10. Misfire must be handled by:

  1. Any worker
  2. Supervisor
  3. Excavator operator
  4. A competent blaster
Correct: d
DGMS rules require trained blaster handling.

11. Sub-drilling ensures:

  1. Reduced bench height
  2. Proper toe breakage
  3. More stemming
  4. Less PF
Correct: b
Extra drilling below the floor ensures toe fragmentation.

12. MIC stands for:

  1. Minimum ignition charge
  2. Maximum instantaneous charge
  3. Mechanical initiation circuit
  4. Mine internal charge
Correct: b
MIC controls vibration.

13. Flyrock is mainly caused by:

  1. Good stemming
  2. Poor stemming / overcharging
  3. Low bench
  4. High spacing
Correct: b
Poor confinement causes uncontrolled rock throw.

14. Pre-splitting helps in:

  1. Increasing PF
  2. Controlling wall damage
  3. Creating toe
  4. Reducing delay timing
Correct: b
Pre-split creates smooth final walls.

15. Stemming prevents:

  1. Sub-drilling
  2. Escape of gases
  3. Spacing errors
  4. Drill deviation
Correct: b
Stemming confines explosive energy.

16. Highest water resistance explosive:

  1. Black powder
  2. ANFO
  3. Permitted explosive
  4. Emulsion explosives
**Correct:** d
Emulsions are highly water-resistant.

17. Flyrock is dangerous because it:

  1. Reduces dust
  2. Can cause fatal injuries
  3. Indicates good blast
  4. Improves fragmentation
Correct: b
Flyrock is the biggest safety hazard.

18. VOD is highest in:

  1. ANFO
  2. Black powder
  3. Emulsion
  4. Watergel
Correct: c
High VOD → better hard-rock fragmentation.

19. DTH drilling uses:

  1. Water pump
  2. Compressor air
  3. Battery
  4. Picks
Correct: b
Compressed air drives hammer + flushing.

20. Major risk in misfire:

  1. No stemming
  2. High spacing
  3. Unexploded explosive remains
  4. No marking
Correct: c
Misfires can detonate later = fatal risk.

21. Bench height depends on:

  1. Truck size
  2. Excavator reach
  3. Explosive type
  4. Weather
Correct: b
Bench must match loader reach safely.

22. Common tunneling cut:

  1. Ring cut
  2. V-cut
  3. Parallel cut
  4. Cross cut
Correct: b
V-cut gives initial relief.

23. Buffer blasting protects:

  1. Magazine
  2. Final walls
  3. Compressor
  4. Drill rigs
Correct: b
Buffer charge = lower damage to final wall.

24. NONEL advantage:

  1. Cheap
  2. High vibration
  3. Not affected by stray electricity
  4. Time consuming
Correct: c
NONEL is safe in electrical noise.

25. Long delays used for:

  1. Small blasts
  2. Large benches
  3. Coal mines
  4. Toe removal
Correct: b
Used in big benches.

26. Line drilling is used for:

  1. Production blasting
  2. Controlled blasting
  3. Secondary blasting
  4. DTH drilling
Correct: b
Creates a plane for smooth walls.

27. Underground long-hole drilling uses:

  1. Hand drills
  2. Jumbo rigs
  3. Top hammer
  4. Manual chisels
Correct: b
Jumbos give accuracy underground.

28. Watergel is a type of:

  1. Powder explosive
  2. Slurry explosive
  3. Permitted explosive
  4. Primer
Correct: b
Watergel = slurry.

29. Cut holes create:

  1. Toe
  2. Initial free face
  3. Stemming
  4. Spacing
Correct: b
Cut holes give relief.

30. Burden controls:

  1. Stemming
  2. Direction of rock throw
  3. Delay timing
  4. Hole deviation
Correct: b
Burden affects breakout direction.

31. Best fragmentation pattern:

  1. Square
  2. Staggered
  3. Ring
  4. Linear
Correct: b
Staggered distributes energy more uniformly.

32. Strongest permitted explosive types:

  1. P1
  2. P2
  3. P3 / P4
  4. P5
Correct: c
Used in fiery UG coal mines.

33. Delay detonators reduce:

  1. Burden
  2. Spacing
  3. Ground vibration
  4. Hole depth
Correct: c
Delay → lower MIC → lower PPV.

34. Burn cut is used for:

  1. OC mining
  2. Tunneling
  3. Toe blasting
  4. Raising charge
Correct: b
Used for development headings.

35. Best explosive for hard rock:

  1. Black powder
  2. ANFO
  3. Permitted explosive
  4. Emulsion explosive
Correct: d
Emulsions have high VOD for hard rock.

36. Toe problems commonly occur due to:

  1. Poor stemming
  2. Insufficient sub-drilling
  3. Large spacing
  4. Low bench height
Correct: b
Toe remains unbroken without enough depth.

37. Typical VOD of ANFO:

  1. 1500 m/s
  2. 3200–4500 m/s
  3. 7000 m/s
  4. 12000 m/s
Correct: b
ANFO has moderate VOD.

38. Pre-splitting uses:

  1. Heavy charge
  2. Light charge
  3. No stemming
  4. Large hole diameter
Correct: b
Light charge produces controlled cracking.

39. Purpose of primer:

  1. Add weight
  2. Initiate main explosive column
  3. Replace detonator
  4. Reduce burden
Correct: b
Primer gives strong initial shock.

40. MIC affects:

  1. Burden
  2. Ground vibration
  3. Toe
  4. Hole deviation
Correct: b
Higher MIC = higher PPV.

41. First step before charging:

  1. Hookup
  2. Stemming
  3. Hole cleaning
  4. Marking
Correct: c
Cleaning ensures proper charge placement.

42. Overbreak is prevented by:

  1. More charge
  2. Controlled blasting techniques
  3. No stemming
  4. Increase burden
Correct: b
Used to protect slope stability.

43. Delay detonators help to:

  1. Increase burden
  2. Increase charge
  3. Control firing sequence
  4. Reduce sub-drilling
Correct: c
Sequencing optimizes fragmentation + vibration.

44. EX-removal means:

  1. Remove stemming
  2. Remove excess explosive
  3. Remove primer
  4. Remove detonator
Correct: b
Avoids overcharging.

45. Inclination means:

  1. Spacing angle
  2. Drill hole angle
  3. Charge direction
  4. PF ratio
Correct: b
Inclined drilling reduces flyrock.

46. Coal blasting uses:

  1. Slurry
  2. Permitted explosives
  3. Emulsion only
  4. Dynamite
Correct: b
Coal mines require flame-proof permitted explosives.

47. Highest hole deviation occurs in:

  1. Top Hammer drilling
  2. DTH
  3. Rotary
  4. Jumbo
Correct: a
Energy loss in rods increases deviation.

48. Best technique for final wall control:

  1. Toe blasting
  2. Heavy charging
  3. Pre-splitting
  4. Staggered pattern
Correct: c
Pre-splitting protects slope walls.

49. Airblast is caused by:

  1. Poor stemming
  2. Dry holes
  3. Wide burden
  4. Slurry explosive
Correct: a
Gas escape = overpressure (airblast).

50. No free face leads to:

  1. Good fragmentation
  2. Backbreak
  3. No drilling
  4. Low VOD
Correct: b
Without relief, rock fractures backward.

51. Fragmentation mainly depends on:

  1. Drill rod color
  2. Bench width
  3. Burden, spacing & charge distribution
  4. Magazine location
Correct: c
Fragmentation is controlled by geometry + energy.

52. Flyrock distance increases when:

  1. Burden is correct
  2. Charge is too high
  3. Stemming is perfect
  4. Delays are long
Correct: b
Overcharging pushes rock violently upward.

53. Ground vibration is measured in:

  1. Hz only
  2. dB
  3. mm/s (PPV)
  4. m/s²
Correct: c
PPV (Peak Particle Velocity) is measured in mm/s.

54. Electronic detonators are preferred because:

  1. Cheapest
  2. Produce more dust
  3. Highly accurate timing
  4. More misfires
Correct: c
Millisecond accuracy → better results, less vibration.

55. The main purpose of sub-drilling is:

  1. Increase stemming
  2. Break the bench toe
  3. Decrease spacing
  4. Increase VOD
Correct: b
Extra depth ensures bottom breakage.

56. Higher burden than required causes:

  1. Good fragmentation
  2. Poor fragmentation
  3. No effect
  4. More flyrock
Correct: b
Too much burden restricts explosive energy.

57. Airblast is measured in:

  1. mm/s
  2. dB (decibel)
  3. Hz
  4. kg/s
Correct: b
Air overpressure is measured in decibels.

58. Staggered pattern is preferred because:

  1. Looks neat
  2. Energy distribution becomes uniform
  3. It needs less drilling
  4. Creates more dust
Correct: b
Staggered layout improves fragmentation.

59. Best explosive for very hard rock:

  1. Black powder
  2. ANFO
  3. Emulsion explosive
  4. Permitted explosive
Correct: c
High VOD handles tough formations.

60. The free face helps:

  1. Rock to move and break freely
  2. Increase vibration
  3. Increase stemming
  4. Increase deviation
Correct: a
Free face gives direction for rock movement.

61. The main purpose of stemming is to:

  1. Increase hole depth
  2. Confine explosive gases
  3. Reduce explosive cost
  4. Reduce spacing
Correct: b
Confined gases → better fragmentation.

62. The most accurate initiation system:

  1. Electric detonators
  2. NONEL
  3. Detonating cord
  4. Electronic detonators
Correct: d
Electronic → millisecond accuracy.

63. Toe problem may occur when:

  1. High VOD
  2. Sub-drilling is insufficient
  3. Delay is long
  4. Spacing is small
Correct: b
Toe requires more energy and depth.

64. Overcharging leads to:

  1. Good fragmentation
  2. No change
  3. Flyrock issues
  4. Less dust
Correct: c
Too much charge pushes rocks uncontrolled.

65. Stemming length is typically:

  1. 0.1 × burden
  2. 0.7 × burden
  3. Equal to hole depth
  4. Twice the charge length
Correct: b
Empirical rule: Stemming = 0.7B.

66. MIC is reduced by:

  1. Short stemming
  2. Higher burden
  3. Using delays
  4. Increasing VOD
Correct: c
Delays reduce instantaneous charge.

67. Which drill has maximum deviation?

  1. Top hammer
  2. DTH
  3. Rotary
  4. Hydraulic
Correct: a
Rod bending increases deviation.

68. Best timing control is obtained by:

  1. NONEL
  2. Electronic detonators
  3. Fuse
  4. Det cord
Correct: b
Highest timing precision.

69. Burden too small leads to:

  1. No effect
  2. Flyrock
  3. Good fragmentation
  4. More dust
Correct: b
Small burden → too much energy → flyrock.

70. Loading unit efficiency depends on:

  1. Truck model
  2. Drill rod type
  3. Fragmentation size
  4. Explosive price
Correct: c
Better fragmentation = faster loading.

71. Water-sensitive explosive:

  1. ANFO
  2. Emulsion
  3. Watergel
  4. Slurry
Correct: a
ANFO cannot be used in wet holes.

72. Flyrock can be minimised by:

  1. More charge
  2. Proper stemming
  3. Short benches
  4. No delays
Correct: b
Stemming absorbs excess energy.

73. Fragmentation improves with:

  1. Low VOD
  2. High VOD explosives
  3. Random spacing
  4. Short stemming
Correct: b
High VOD breaks dense rock effectively.

74. DTH drilling is best for:

  1. Soft clay
  2. Hard, compact rock
  3. Sand
  4. Loose gravel
Correct: b
DTH gives deep penetration in hard formations.

75. Which helps reduce PPV?

  1. High MIC
  2. Using delays
  3. Overcharging
  4. Short stemming
Correct: b
Delays reduce peak energy release.

76. Drill bit selection depends on:

  1. Operator age
  2. Color of bit
  3. Rock hardness
  4. Weather
Correct: c
Rock properties decide bit type.

77. Electronic detonators provide:

  1. Lowest cost
  2. High current risk
  3. Best timing accuracy
  4. No advantage
Correct: c
Highly accurate firing delays.

78. Fragmentation is evaluated by:

  1. Sound of blast
  2. Dust amount
  3. Sieve analysis
  4. Bench height
Correct: c
Actual size distribution is measured by sieving.

79. Not a fragmentation parameter:

  1. Spacing
  2. Burden
  3. Charge length
  4. Operator age
Correct: d
Human factors do not affect fragmentation physics.

80. Decoupled charge is used to:

  1. Increase VOD
  2. Reduce vibration
  3. Increase PF
  4. Increase dust
Correct: b
Lower coupling reduces transmitted energy.

81. Ground vibration is measured using:

  1. pH meter
  2. Thermometer
  3. Seismograph
  4. Weigh bridge
Correct: c
Seismographs record PPV & frequency.

82. Cast blasting is used to:

  1. Increase PF
  2. Throw rock to waste dump
  3. Reduce overbreak
  4. Increase stemming
Correct: b
Used in coal OB removal.

83. Buffer is used to:

  1. Blast more rock
  2. Protect final wall
  3. Create toe
  4. Increase dust
Correct: b
Lower energy protects walls.

84. To reduce flyrock:

  1. Increase charge
  2. Increase stemming
  3. Remove burden
  4. Use no delays
Correct: b
Stemming = primary protection.

85. Explosive magazine must follow:

  1. Personal rules
  2. DGMS rules
  3. Truck rules
  4. No rules
Correct: b
Magazine storage follows DGMS Safety Rules.

86. Overbreak is reduced by:

  1. Overcharging
  2. Pre-splitting
  3. No stemming
  4. Short spacing
Correct: b
Pre-split protects slope face.

87. Trim blast is used to:

  1. Break toe
  2. Clean wall for final shaping
  3. Increase PF
  4. Lower burden
Correct: b
Trim blast finishes the wall.

88. Environmental issue in blasting:

  1. Ventilation
  2. Dust & vibration
  3. Better fragmentation
  4. More trucks
Correct: b
Dust + vibration = main concerns.

89. When blasting near structures:

  1. Increase charge
  2. Reduce MIC
  3. Use no stemming
  4. Increase spacing
Correct: b
Lower MIC reduces vibration.

90. Stemming length (rule of thumb):

  1. 0.2 × burden
  2. 0.7 × burden
  3. Equal to bench height
  4. 2 × charge length
Correct: b
Most common empirical ratio.

91. Misfires mostly caused by:

  1. Good priming
  2. Poor connection
  3. Strong detonator
  4. Perfect stemming
Correct: b
Loose/damaged cords cause misfires.

92. Large burden causes:

  1. Backbreak
  2. Good fragmentation
  3. No effect
  4. Lower vibration
Correct: a
Too much burden → uncontrolled backward fracture.

93. Thin seam blasting uses:

  1. Heavy blasting
  2. Contour / cast blasting
  3. Toe blasting
  4. No stemming
Correct: b
Cast blasting is economical for thin seams.

94. Misfire must be handled after:

  1. 2 minutes
  2. Mandatory waiting period
  3. No wait needed
  4. Throwing water
Correct: b
DGMS rules require waiting before approach.

95. Safest in electrically noisy areas:

  1. Electric detonators
  2. NONEL system
  3. Det cord
  4. Fuse
Correct: b
NONEL is immune to stray currents.

96. Blasting safety regulator in India:

  1. SEBI
  2. DGMS
  3. ISRO
  4. GAIL
Correct: b
DGMS regulates mining safety.

97. Flyrock throw distance increases by:

  1. Low charge
  2. High charge + poor stemming
  3. High burden
  4. Good delays
Correct: b
Energy escapes upward → long throw.

98. Emulsions advantage over ANFO:

  1. Lower VOD
  2. Higher VOD & water resistance
  3. Cheaper
  4. Less reliable
Correct: b
Better performance in wet/hard rock.

99. Charge per hole depends on:

  1. Explosive colour
  2. Rock density & fragmentation target
  3. Magazine name
  4. Blaster’s age
Correct: b
Charge must match rock hardness + design.

100. Dust can be reduced by:

  1. Long delays
  2. Water spraying
  3. More charge
  4. No stemming
Correct: b
Water reduces suspended dust.

101. A bench cut is used to:

  1. Cut trees near bench
  2. Create an initial free face
  3. Increase stemming
  4. Reduce drill depth
Correct: b
Bench cut holes open the face to allow the main blast to break effectively.

102. To improve fragmentation in very hard rock you would typically:

  1. Reduce charge energy
  2. Increase explosive energy (higher VOD or charge)
  3. Use shallower holes
  4. Remove stemming
Correct: b
Hard rock requires more energy per unit volume for efficient breakage.

103. Dividing the charge into delays helps to:

  1. Increase MIC
  2. Lower peak vibration (PPV)
  3. Cause more flyrock
  4. Reduce hole depth
Correct: b
Sequencing spreads energy over time, reducing instantaneous peak ground motion.

104. Feathered or decoupled holes are commonly used in:

  1. Bulk ANFO charging
  2. Pre-splitting operations
  3. Magazine storage
  4. Primer manufacture
Correct: b
Decoupling reduces energy transmitted to the rock and aids controlled fracture planes.

105. Poor drill hole alignment typically causes:

  1. Better fragmentation
  2. Irregular breakage and higher misfire risk
  3. Lower vibration
  4. Shorter stemming requirement
Correct: b
Misaligned holes change energy distribution, causing uneven breakage and initiation problems.

106. Scaled distance is used to predict:

  1. Hole deviation
  2. Ground vibration (PPV) at a distance
  3. Explosive shelf life
  4. Stemming length
Correct: b
Scaled distance relates charge weight to distance to estimate PPV and compliance with limits.

107. A key safety measure at a blast site is:

  1. Allowing anyone near the blast
  2. Clear exclusion zones and signalling
  3. Removing signs to save cost
  4. Using untrained personnel
Correct: b
Controlled access, fencing and audible/visual warnings reduce accidental injuries.

108. Blast design charts are primarily used to:

  1. Decorate the office
  2. Guide burden, spacing and charge selection
  3. Increase misfires
  4. Calculate operator salary
Correct: b
They codify empirical relationships for consistent blast planning.

109. In poor visibility (fog), before firing a blast you must:

  1. Proceed as normal
  2. Ensure warning systems and visual clearance are effective
  3. Skip evacuation
  4. Use larger charges
Correct: b
If visibility is limited, alternative checks are needed to guarantee safety and evacuation.

110. To reduce airblast you should:

  1. Overcharge near surface
  2. Increase stemming and reduce surface charge
  3. Use no delays
  4. Make shallower holes
Correct: b
Proper stemming confines gases and reducing surface charge lowers overpressure.

111. Portable seismographs are used to:

  1. Measure temperature
  2. Record PPV and frequency after blasts
  3. Measure humidity
  4. Check stemming length
Correct: b
Portable vibration monitors log data for regulatory and design use.

112. Proper primer placement is critical to:

  1. Make holes deeper
  2. Ensure reliable initiation of the explosive column
  3. Increase dust
  4. Reduce drill life
Correct: b
Primer bridges detonator energy into the main charge to achieve full detonation.

113. Safe charging operations require:

  1. Untrained helpers
  2. Trained blasters, PPE and controlled access
  3. Open public access
  4. Loose storage of detonators
Correct: b
Competence, PPE and exclusion zones are essential for charging safety.

114. A sign of poor fragmentation is:

  1. Uniform small particles
  2. High proportion of oversized boulders
  3. Fast loading
  4. Low recycle
Correct: b
Oversize indicates insufficient energy distribution or poor design.

115. Corrective action for persistent toe problems:

  1. Decrease bottom charge
  2. Increase bottom charge or sub-drilling
  3. Remove primers
  4. Reduce stemming
Correct: b
More energy at the toe or deeper holes helps break toe material effectively.

116. Personnel handling explosives must have:

  1. Driver licence
  2. Certified blaster training
  3. Cooking certificate
  4. No qualification
Correct: b
Regulations require certification and training for safe handling.

117. After a blast, before re-entry you must:

  1. Rush in immediately
  2. Conduct post-blast inspection and clear fumes/hazards
  3. Collect explosives
  4. Start loading without checks
Correct: b
Check for misfires, gases and unstable ground before allowing access.

118. Blast reports are important to:

  1. Replace daily logs
  2. Record performance, compliance and inform future design
  3. Calculate wages
  4. Hide mistakes
Correct: b
Reports document outcomes, vibration data and lessons for optimisation.

119. To avoid sympathetic detonation you should:

  1. Place charges very close
  2. Maintain safe spacing and use delays
  3. Use identical timing only
  4. Remove stemming
Correct: b
Spacing and sequencing prevent unintended initiation of adjacent charges.

120. Most cost-effective explosive for bulk open-pit ops is:

  1. Emulsion
  2. ANFO
  3. Permitted explosive
  4. Black powder
Correct: b
ANFO is inexpensive and effective where water isn’t an issue.

121. Field evaluation of a blast is done by:

  1. Counting holes
  2. Sieve analysis and productivity tracking
  3. Visual smell
  4. No checking
Correct: b
Combining fragmentation analysis with loading rates shows efficiency.

122. Hole diameter selection depends mainly on:

  1. Magazine color
  2. Type of explosive and required charge volume
  3. Operator height
  4. Weather only
Correct: b
Diameter must suit explosive form (cartridge/bulk) and energy needs.

123. To improve fragmentation without raising explosive cost you should:

  1. Use larger holes
  2. Optimize burden/spacing and delays
  3. Shorten stemming drastically
  4. Increase bench height
Correct: b
Better design and timing often yield fragmentation gains without extra explosives.

124. A sign of a potential misfire is:

  1. Clean muck pile
  2. Unexploded charges visible or silent sections
  3. Good fragmentation
  4. Low dust
Correct: b
Lack of detonation sound or visible unexploded material indicates misfire.

125. In heavily jointed rock fragmentation improves with:

  1. Single large charges
  2. Smaller charge per hole and staggered delays
  3. Ignoring joints
  4. Increasing stemming only
Correct: b
Controlled energy distribution exploits natural joints for better breakage.

126. Securing a blast site from public access requires:

  1. Leave site open
  2. Fencing, signage and authorized access only
  3. Allow public viewing
  4. No action
Correct: b
Proper security prevents accidental injuries and legal issues.

127. A key output of blast design software is:

  1. Operator pay
  2. Optimized burden, spacing and delay sequence
  3. Magazine layout
  4. Noise levels only
Correct: b
Software simulates energy distribution for improved planning.

128. Charge distribution down the hole is affected by:

  1. Explosive color
  2. Column length and density distribution
  3. Only stemming
  4. Only delay type
Correct: b
How mass is placed along hole depth influences how energy is delivered.

129. A reason NOT to perform blast monitoring is:

  1. Regulatory compliance
  2. Evaluate environmental impact
  3. To increase magazine stock illegally
  4. Improve future designs
Correct: c
Monitoring is for safety and optimisation, not illicit purposes.

130. To manage vibration-induced damage to buildings you should:

  1. Ignore regulations
  2. Use scaled distance and keep PPV below limits
  3. Use larger charges near buildings
  4. No action
Correct: b
Scaled distance helps set charge weights to meet allowable PPV for structures.

131. Electronic timing advantage over NONEL is:

  1. Lower cost always
  2. Programmable delays with highest precision
  3. No training required
  4. Less accuracy
Correct: b
Programmable millisecond control allows advanced sequencing strategies.

132. Misfires can be reduced by:

  1. Poor storage
  2. Proper handling, testing and weatherproofing
  3. Using expired explosives
  4. No training
Correct: b
Good procedures and QC minimise misfire incidents.

133. The main goal when blasting near populated areas is to:

  1. Maximise debris throw
  2. Minimise vibration, airblast and flyrock
  3. Use cheapest explosives
  4. Ignore complaints
Correct: b
Community safety and impact management are paramount.

134. Noise from blasts is best reduced by:

  1. Using larger charges
  2. Delay sequencing and encapsulated charges
  3. Blasting late at night always
  4. No action
Correct: b
Sequencing and encapsulation reduce acoustic impulse transmission.

135. A direct sign of detonation failure is:

  1. Clean muck pile
  2. Unblasted columns or heavy undersize
  3. Good fragmentation
  4. Low dust
Correct: b
Unblasted material indicates initiation problems.

136. Safe storage of explosives requires:

  1. Close to worker dorms
  2. Secure magazine, distance from operations and authorized access
  3. Open sun exposure
  4. Store with fuel
Correct: b
Proper magazine design and security reduce risks of theft/accidental initiation.

137. Main reason to use decoupled charges is to:

  1. Raise VOD
  2. Lower transmitted vibration
  3. Increase flyrock
  4. Reduce stemming
Correct: b
Decoupling reduces the coupling of explosive energy to the rock mass.

138. When using ANFO in damp holes you should:

  1. Do nothing special
  2. Ensure hole is dry or use water-resistant boosters
  3. Use more charge
  4. Shorten stemming
Correct: b
ANFO is water sensitive—booster/keep hole dry for reliable initiation.

139. Column length and charge per delay calculations are based on:

  1. Operator age
  2. Hole volume and rock properties
  3. Magazine distance only
  4. No data
Correct: b
Column design uses hole geometry and rock data to set charge mass and distribution.

140. Sites use electronic detonators despite cost because they:

  1. Reduce precision
  2. Provide precision and reduced environmental impact
  3. Are lighter
  4. No reason
Correct: b
Precision reduces MIC and helps control blast impacts better than cheaper options.

141. To improve bench face stability use:

  1. Random blasting
  2. Pre-splitting and controlled charging
  3. No inspection
  4. Heavy overbreak
Correct: b
These techniques protect slope integrity and reduce overbreak.

142. To avoid sympathetic detonation you should:

  1. Place holes closer
  2. Stagger firing times and maintain spacing
  3. Use more primer
  4. Remove stemming
Correct: b
Sequencing and geometry prevent one hole’s initiation from causing others unintentionally.

143. When repositioning a magazine you must:

  1. Move without notice
  2. Notify authorities and follow licensing conditions
  3. Bring public near magazine
  4. No action required
Correct: b
Relocation must comply with legal requirements for safety and legality.

144. Acceptable approach to a misfire is to:

  1. Approach immediately
  2. Follow misfire protocol—wait then inspect with competent personnel
  3. Use water to flush hole
  4. Remove charge manually
Correct: b
Certified blasters handle misfires per established safety procedures.

145. Which variable is least likely to change from blast to blast on a fixed bench?

  1. Charge per hole
  2. Delay timing
  3. Bench geometry
  4. Explosive type
Correct: c
Bench geometry remains constant unless the bench design changes.

146. Environmental management for blasting must consider:

  1. Only production
  2. Mitigating dust, vibration and noise impacts
  3. Increase flyrock
  4. No reporting
Correct: b
Community relations and legal compliance require mitigation measures and monitoring.

147. In wet conditions, detonator reliability improves with:

  1. Expired detonators
  2. Waterproof detonators and protective enclosures
  3. Exposing detonators to water
  4. No protection
Correct: b
Waterproofing maintains circuit integrity and reduces misfires in damp environments.

148. After a blast, required safety checks include:

  1. Immediate re-entry
  2. Gas testing, visual inspection and clearance by competent person
  3. No checks
  4. Ignore misfires
Correct: b
Verification prevents exposure to toxic gases and unstable ground.

149. Reduce charge per delay while keeping fragmentation by:

  1. Using a single long delay
  2. Increasing number of delays with electronic timing
  3. Increasing hole diameter only
  4. Removing stemming
Correct: b
More precise delays allow spreading energy without large instantaneous charges.

150. To ensure compliance with blasting regulations the best approach is:

  1. Ignore audits
  2. Maintain documentation, training and periodic audits
  3. Store explosives without records
  4. No safety policy
Correct: b
Systematic management, records and audits demonstrate due diligence and compliance.

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