💥 Explosives in Mining – Types, Properties, and Safety
📌 Introduction Explosives are substances or mixtures that, when subjected to
shock, impact, heat, or friction, undergo instantaneous chemical transformation, releasing a
large volume of high-temperature gases at high pressure. This rapid reaction causes
shattering, blasting, and demolition, making explosives an essential part of mining operations. They are manufactured using
fuels, oxidizers, sensitizers, energizers, and other additives, combined in specific proportions to achieve the desired strength and safety.
⚡ Detonation vs Deflagration - Explosion: Self-propagating exothermic reaction producing gases at high pressure and temperature.
- Detonation:
- Propagation of shock waves through an explosive charge.
- Velocity of detonation (VOD): 1500–9000 m/s (above speed of sound).
- Produces shattering effect.
- Deflagration:
- Extremely rapid burning, but below the speed of sound.
- Produces heat and gas without shock waves.
🔹 Ingredients of Explosives | Category | Examples |
| Fuels | Fuel oil, carbon, aluminum, TNT |
| Oxidizers | Ammonium Nitrate (AN), Sodium Nitrate, Calcium Carbonate |
| Sensitizers | NG, TNT, Nitro-starch, Aluminum |
| Energizers | Metallic powders (Al, Mg) |
| Misc. Agents | Water, thickeners, gelatinizers, emulsifiers, stabilizers, flame retarders |
- Main elements: Oxygen, Nitrogen, Hydrogen, Carbon, Aluminum, Magnesium, Sodium, Calcium.
🔒 Classification of Explosives 1️⃣ Permitted Explosives - Designed for underground coal mines to avoid methane and coal dust explosions.
- Forms: Granular, Gelatinous, Slurry.
- Gelatinous types suited for wet conditions.
- Velocity of detonation: 6000–16,000 ft/sec.
- Contain cooling agents like NaCl, KCl, or Ammonium Chloride.
- Sheathed explosives (sodium bicarbonate cover) also permitted in coal mines.
🔥 Blasting Properties of Explosives a) Strength - Energy released per unit weight or volume.
- Expressed relative to ANFO = 100%.
- Tests: Trauzl lead block test.
- Parameters: VOD, gas volume, energy, detonation pressure, explosion temperature.
b) Detonation Velocity (VOD) - Speed of detonation waves (1500–6700 m/s).
- Factors: Explosive type, diameter, confinement, temperature, priming.
- Higher VOD = higher shattering effect.
c) Density - Range: 0.5–1.7 g/cc.
- Higher density → more energy/unit volume → useful in hard strata.
- Every explosive has a critical density, above which detonation fails.
d) Water Resistance - Ability to withstand water without losing sensitivity.
- ANFO: Poor water resistance.
- Slurries: Good.
- NG-based explosives: Best.
e) Fume Characteristics - Good explosive → generates minimum toxic gases (CO, NOx).
- Range: 0.023–0.094 m³/kg.
- NG explosives may cause health hazards (headache).
f) Oxygen Balance - Ratio of oxidizers to fuels.
- Excess oxygen → toxic gases (NOx).
- Oxygen deficiency → Carbon monoxide.
- Example: ANFO (Ammonium Nitrate + Fuel Oil).
g) Detonation Pressure - Formula: P = 2.5 × ρ × v² × 10⁻⁶ (KB)
- ρ = density (g/cc), v = velocity (m/s).
- Range: 5–150 KB.
- Higher pressure = higher brisance (shattering ability).
h) Borehole Pressure & Critical Diameter - Borehole pressure: 10–60 KB.
- Critical diameter: Minimum diameter below which detonation fails → risk of misfire.
i) Sensitivity - Ability of an explosive to propagate detonation wave between cartridges.
- Important for primer selection.
j) Handling & Storage Safety - ANFO: Hygroscopic, poor storage quality, can irritate skin.
- Some explosives deform under high temperature.
- Tests for sensitivity:
- Impact Test (fall hammer)
- Friction Pendulum Test
- Projectile Impact Test
- Bullet Sensitivity Test
📖 Exam-Oriented Points (DGMS Focus) - Definition of Explosives: Fuels + Oxidizers + Sensitizers + Energizers.
- Difference between Detonation & Deflagration.
- Permitted Explosives: Contain cooling agents (NaCl, KCl, NH₄Cl).
- Key Properties: Strength, VOD, Density, Water Resistance, Oxygen Balance.
- Important Formula: Detonation Pressure P = 2.5 ρ v² × 10⁻⁶ KB.
- Tests: Trauzl block, Ballistic mortar, Lead block test.
- Critical Diameter: Below which detonation fails → misfire.
Q1. An explosive undergoes instantaneous chemical transformation into gases with high temperature and pressure when subjected to: A) Only shock B) Only friction
C) Shock, heat, friction, or spark
D) Only ignition
E) Only pressure ✅
Answer: C
Explanation: Explosives can be initiated by multiple stimuli like shock, heat, friction, spark, or ignition.
Q2. The process of shock wave propagation through an explosive charge is called: A) Explosion
B) Deflagration
C) Detonation
D) Combustion
E) Ignition ✅
Answer: C
Explanation: Detonation is propagation of shock waves through an explosive at supersonic speed (1500–9000 m/s).
Q3. Deflagration differs from detonation in that: A) It produces no gas
B) It occurs below the speed of sound
C) It is faster than detonation
D) It requires no heat
E) It is non-exothermic ✅
Answer: B
Explanation: Deflagration is rapid burning, but at subsonic speed (below sound).
Q4. The main elements found in explosives include: A) Oxygen, Nitrogen, Hydrogen, Carbon
B) Only Oxygen and Carbon
C) Only Nitrogen and Hydrogen
D) Only Metals like Al, Mg
E) None ✅
Answer: A
Explanation: Primary elements: O, N, H, C; plus metals like Al, Mg, Na, Ca.
Q5. Permitted explosives are designed for: A) Metal mines
B) Surface blasting
C) Underground coal mines
D) Tunnel excavation
E) Quarry blasting ✅
Answer: C
Explanation: Permitted explosives are specifically designed to prevent methane–coal dust explosions in underground coal mines.
Q6. Cooling agents in permitted explosives include: A) Sodium chloride
B) Potassium chloride
C) Ammonium chloride
D) All of the above
E) None ✅
Answer: D
Explanation: All these salts act as cooling agents to suppress incendive flames.
Q7. A sheathed explosive in coal mines refers to: A) Explosive covered with plastic
B) Explosive wrapped with sodium bicarbonate layer
C) Explosive mixed with aluminium
D) Explosive dipped in water
E) Explosive coated with wax ✅
Answer: B
Explanation: Sheathed explosives are cartridges wrapped with 3 mm sodium bicarbonate sheath.
Q8. Explosive strength is measured relative to: A) TNT = 100%
B) ANFO = 100%
C) RDX = 100%
D) Gelatin = 100%
E) NG = 100% ✅
Answer: B
Explanation: Explosive strength is expressed relative to ANFO (standard = 100%).
Q9. Trauzl lead block test is used to measure: A) Oxygen balance
B) Detonation velocity
C) Strength of explosives
D) Sensitivity
E) Fume quality ✅
Answer: C
Explanation: Trauzl lead block test measures the strength (energy) of explosives.
Q10. Velocity of detonation (VOD) of explosives generally ranges from: A) 100–500 m/s
B) 1500–6700 m/s
C) 7000–10,000 m/s
D) 50–100 m/s
E) None ✅
Answer: B
Explanation: VOD ranges between 1500–6700 m/s; higher VOD → better shattering.
Q11. Higher VOD explosives are preferred for: A) Soft rocks
B) Weakly fractured rocks
C) Hard rocks
D) Clayey strata
E) All conditions ✅
Answer: C
Explanation: High shattering effect of high VOD is suitable for hard rocks.
Q12. Density of explosives usually lies between: A) 0.1–0.5 g/cc
B) 0.5–1.7 g/cc
C) 2–3 g/cc
D) 3–5 g/cc
E) 5–10 g/cc ✅
Answer: B
Explanation: Explosives typically have density between 0.5 and 1.7 g/cc.
Q13. Which explosive has poor water resistance? A) ANFO
B) Slurry
C) Gelatinous explosives
D) NG-based explosives
E) Emulsion explosives ✅
Answer: A
Explanation: ANFO absorbs water easily and loses sensitivity → poor water resistance.
Q14. Fume characteristics of explosives refer to: A) Quantity of useful gases
B) Toxic gases produced
C) Velocity of detonation
D) Explosion temperature
E) Energy output ✅
Answer: B
Explanation: Good explosives should produce minimal toxic gases like CO, NOx.
Q15. Oxygen balance in explosives is necessary to: A) Increase strength
B) Avoid excessive fumes
C) Control energy generation
D) Both B and C
E) None ✅
Answer: D
Explanation: Proper oxygen balance reduces toxic fumes and regulates energy output.
Q16. Detonation pressure (P) is calculated using: A) P = ρ × g × h
B) P = 2.5 ρ v² × 10⁻⁶
C) P = m × a
D) P = F/A
E) P = E/t ✅
Answer: B
Explanation: Detonation pressure formula:
P = 2.5 ρ v² × 10⁻⁶ KB.
Q17. Borehole pressure of explosives generally lies between: A) 1–5 KB
B) 5–10 KB
C) 10–60 KB
D) 100–200 KB
E) None ✅
Answer: C
Explanation: Borehole pressure typically ranges from 10 to 60 KB.
Q18. Critical diameter of an explosive is: A) Diameter at which explosive fails to store
B) Minimum diameter below which detonation cannot proceed
C) Maximum permissible diameter of cartridge
D) Borehole diameter
E) None ✅
Answer: B
Explanation: Critical diameter is the minimum charge diameter below which detonation stops.
Q19. Sensitivity of an explosive is measured as: A) Ability to resist water
B) Ability to withstand pressure
C) Ability to propagate detonation wave across a gap
D) Energy per unit volume
E) None ✅
Answer: C
Explanation: Sensitivity is the explosive’s ability to propagate detonation between charges.
Q20. ANFO has poor storage quality because: A) It evaporates at low temperature
B) It is hygroscopic in nature
C) It is very dense
D) It is insensitive to detonation
E) It emits toxic fumes ✅
Answer: B
Explanation: ANFO absorbs moisture (hygroscopic), reducing efficiency and storage life.
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