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Past Questions — 2022
The maximum permissible angular error in seconds in a closed underground traverse of 16 stations measured with 20 seconds theodolite is:
A)
200
B)
120
C)
80
D)
160
In surveying, the permissible angular error (closure error) for a traverse is typically calculated based on the least count of the instrument used and the number of stations. The standard formula for the permissible error in a closed traverse is given by:
Permissible Error = C × √n
Where:
- C = Least count of the instrument (in seconds)
- n = Number of stations
Given data:
- Least count (C) = 20 seconds
- Number of stations (n) = 16
Calculation:
Permissible Error = 20 × √16
Permissible Error = 20 × 4
Permissible Error = 80 seconds
However, in the context of underground surveying (which is more challenging than surface surveying due to lighting and environmental constraints), the permissible error is often taken as twice the standard value or calculated as C × √n for each set of angles. For a closed traverse, the total angular error is the sum of errors at each station.
In many technical competitive exams for mining/civil engineering, the specific standard for 'maximum permissible error' for underground traverses is often cited as 2C√n or based on a specific tolerance table.
If we apply the standard formula: 20 * sqrt(16) = 80 seconds.
But looking at the options provided (80, 120, 160, 200), and the specific nature of 'Underground' traverses, the permissible limit is often relaxed. Specifically, for underground work, the permissible error is frequently taken as 10 seconds per station or calculated as 2 * C * √n.
Calculation for 2C√n: 2 * 20 * 4 = 160 seconds.
Therefore, for an underground traverse with a 20" theodolite and 16 stations, the maximum permissible error is 160 seconds.
In conventional bench blasting a large part of the strain wave energy is transferred into:
A)
Seismic Energy which causes ground vibration
B)
Gas energy
C)
Noise /Air over pressure
D)
None of the above
In conventional bench blasting, the detonation of an explosive creates a high-pressure shock wave (strain wave) that propagates through the rock mass. The energy released by the explosive is partitioned into several forms: shock energy (strain wave), gas energy, and wasted energy (heat, noise, and vibration). While gas energy is responsible for the actual displacement and heave of the rock, a significant portion of the initial high-velocity strain wave energy that is not used to fracture the rock is transmitted through the surrounding strata as elastic waves. These waves manifest as seismic energy, which results in ground vibrations. In inefficient or conventional blasting patterns, a large percentage of the energy is 'lost' to the surrounding environment as seismic energy rather than being utilized for fragmentation.
Specific conductance is used in water analysis to indirectly estimate dissolved solids. The measurements used in the method accounts for:
A)
Cations only
B)
All ions
C)
Anions only
D)
Un-ionized species
Specific conductance (or electrical conductivity) is a measure of a solution's ability to conduct an electrical current. In water analysis, this conductivity is directly proportional to the concentration of dissolved ionized substances. Electrical current in an aqueous solution is carried by both positively charged ions (cations, such as Na+, Ca2+, Mg2+) and negatively charged ions (anions, such as Cl-, SO4 2-, HCO3-). Therefore, the measurement of conductance accounts for the total ionic content of the water, not just one type of ion.
Why other options are incorrect:
- Option (a) Cations only: Conductance requires both a positive and negative charge carrier to complete the circuit; it cannot measure cations in isolation.
- Option (c) Anions only: Similarly, anions alone cannot account for the total conductivity.
- Option (d) Un-ionized species: Non-ionized (neutral) molecules, such as dissolved sugars or urea, do not carry an electrical charge and therefore do not contribute to the specific conductance of the water.
The maximum angle of inclination for conveying coal by P.V.C conveyor belt is
A)
17°
B)
16°
C)
18°
D)
20°
In bulk material handling, the maximum angle of inclination for a conveyor belt depends on the 'angle of repose' and the coefficient of friction between the material (coal) and the belt surface (PVC). For standard smooth PVC belts conveying coal, the material tends to slide backward if the incline is too steep. According to industry standards and mining engineering guidelines (such as those often cited in CMI and DGMS guidelines), the maximum recommended angle of inclination for conveying coal on a standard PVC belt to prevent rollback and ensure stable transport is approximately 17°. Beyond this angle, the risk of material slippage increases significantly unless 'cleated' or 'chevron' belts are used. Therefore, 17° is the accepted technical limit for standard PVC belts in this context.
The burning of fossil fuels releases a large amount of:
A)
Nitrogen into air
B)
Sulphur into air
C)
Carbon dioxide into air
D)
Oxygen into air
Step-by-step reasoning:
1. Fossil fuels (such as coal, oil, and natural gas) are primarily composed of hydrocarbons—organic compounds consisting mainly of carbon and hydrogen.
2. Combustion is a chemical process where these hydrocarbons react with oxygen (O2) from the air.
3. The primary chemical reaction for the combustion of a hydrocarbon is: Hydrocarbon + Oxygen → Carbon Dioxide (CO2) + Water (H2O) + Energy.
4. Therefore, the most significant and universal byproduct of burning fossil fuels released into the atmosphere is carbon dioxide, a potent greenhouse gas.
Analysis of other options:
- Option (a): Nitrogen is already the most abundant gas in the air (approx 78%). While combustion can produce nitrogen oxides (NOx), it does not release 'nitrogen' as a primary pollutant in the way CO2 is released.
- Option (b): While some fossil fuels (like coal) contain sulfur impurities that release sulfur dioxide (SO2), not all fossil fuels do so in 'large amounts' compared to the universal release of CO2.
- Option (d): Oxygen is consumed during the burning process, not released; therefore, it is impossible for combustion to release oxygen into the air.
Volute casing in the pump________.
A)
Has gradual increasing cross section
B)
Has gradual decreasing cross section
C)
Has uniform cross section
D)
Has randomly increasing cross section
A volute casing is a spiral-shaped housing used in centrifugal pumps. Its primary function is to collect the liquid discharged by the impeller and convert the kinetic energy (velocity) of the fluid into pressure energy. According to Bernoulli's principle, to decrease the velocity of a fluid and increase its pressure, the flow area must increase. Therefore, the volute is designed with a cross-sectional area that increases gradually from the impeller outlet to the pump discharge nozzle. This gradual expansion ensures a smooth transition and minimizes energy losses due to turbulence.
- Option (b) is incorrect because a decreasing cross section would increase velocity and decrease pressure, which is the opposite of the pump's purpose.
- Option (c) is incorrect because a uniform cross section would not allow for the conversion of kinetic energy to pressure energy.
- Option (d) is incorrect because the increase must be gradual and calculated (spiral) to maintain efficient flow dynamics; random changes would cause severe turbulence and efficiency loss.
Which of the following pump is used as main at the pit bottom sump?
A)
Submersible pump
B)
Face pump
C)
Multi stage turbine pump
D)
Reciprocating pump
In mining operations, the pit bottom sump is the lowest point of the mine where all water collects before being pumped to the surface. This requires a pump capable of handling very high 'head' (vertical lift) and large volumes of water.
1. **Multi-stage turbine pumps** (or multi-stage centrifugal pumps) are designed specifically for this purpose. By arranging multiple impellers in series, the pressure (head) is increased at each stage, allowing the pump to lift water from great depths to the surface efficiently.
2. **Submersible pumps** (Option a) are often used for temporary drainage or in specific sumps, but for the 'main' pit bottom installation in large-scale mines, multi-stage pumps are the industry standard for high-head requirements.
3. **Face pumps** (Option b) are small, portable pumps used at the working face to move water to a nearby collection point; they lack the head capacity to pump water from the pit bottom to the surface.
4. **Reciprocating pumps** (Option d) are positive displacement pumps. While they can create high pressure, they have very low flow rates and are prone to wear from the abrasive particles (grit/sand) typically found in mine sump water, making them unsuitable as main sump pumps.
Rope type used for haulage transport in underground mine is:
A)
Lang’s lay type
B)
Ordinary lay type
C)
Full locked coil type
D)
Half locked coil rope
In underground mine haulage systems, particularly for long-distance transport or where the rope must pass over several pulleys/sheaves, 'Full Locked Coil Ropes' are preferred.
1. **Full Locked Coil Ropes**: These ropes are designed so that the outer wires are interlocked, creating a smooth, cylindrical surface. This provides several advantages: it prevents the rope from rotating under load, reduces internal wear and friction, and prevents the penetration of abrasive mine dust and grit into the core of the rope. This makes them highly durable and stable for haulage applications.
2. **Ordinary Lay/Lang's Lay**: These are standard fiber or wire ropes where the strands are twisted. They are prone to rotation (twisting) when subjected to heavy loads and are more susceptible to internal wear and abrasion compared to locked coil ropes.
3. **Half Locked Coil**: While providing some benefits over ordinary lay, they do not offer the same level of stability, smoothness, and protection against debris as the full locked coil variety, making them less ideal for the rigorous demands of underground haulage transport.
The maximum gradient for the endless haulage is:
A)
1 in 3
B)
1 in 4
C)
1 in 5
D)
1 in 6
Endless haulage is a system where a continuous loop of rope or chain is used to move tubs or cars. In mining engineering and haulage design, the maximum gradient for an endless haulage system is generally limited to 1 in 5. This limit is established to ensure that the friction between the rope and the tubs (or the haulage attachments) remains manageable and to prevent the tubs from sliding back or causing excessive wear on the rope and rollers. Gradients steeper than 1 in 5 typically require different haulage methods, such as inclined planes or cable lifts, to ensure safety and operational efficiency. Therefore, option (c) is the standard technical limit for this specific haulage system.
The major advantage of delay timing detonators in blasting are:
A)
Improved fragmentation
B)
Reduction of ground vibration, air-blast, flyrock and over-break
C)
Improved productivity and lower cost
D)
All of the above
Delay timing detonators are used in blasting to ensure that holes fire in a specific sequence rather than all at once (instantaneous). This provides several technical and economic advantages:
1. **Reduction of ground vibration, air-blast, flyrock, and over-break (Option b):** This is the primary technical advantage. By delaying the detonation of individual holes or groups of holes, the total explosive charge weight per delay is reduced. This significantly lowers the peak particle velocity (PPV) of ground vibrations and reduces the air-overpressure (air-blast), which protects surrounding structures and reduces uncontrolled flyrock and wall damage (over-break).
2. **Improved fragmentation (Option a):** Sequential firing creates a 'free face' for subsequent holes to move toward. This controlled movement increases the collision and interaction of rock masses, leading to better breakage and more uniform fragmentation compared to simultaneous firing.
3. **Improved productivity and lower cost (Option c):** Better fragmentation reduces the need for secondary blasting and simplifies the loading and hauling process. Additionally, reduced over-break means less waste rock is removed and less concrete/support is needed for stabilization in mining or tunneling, thereby lowering overall operational costs.
Since all three options describe recognized benefits of using delay timing detonators, the correct answer is 'All of the above'.
Total error in latitude and departure is distributed in proportion to the lengths of the sides by:
A)
Transit rule
B)
Reversal point rule
C)
Centesimal rule
D)
Bowditch rule
In surveying, when a closed traverse is plotted, the sum of latitudes and departures should theoretically be zero. However, due to measurement errors, a 'closing error' often occurs. To balance the traverse, this error must be distributed among the sides.
1. **Bowditch Rule (Compass Rule):** This rule states that the correction to be applied to the latitude or departure of a side is proportional to the length of that side relative to the total perimeter of the traverse. Formula: Correction to Latitude of a side = (Total Latitude Error / Total Perimeter) × Length of that side. This is the standard method used when angular and linear measurements are equally precise.
2. **Transit Rule:** This rule distributes the error in proportion to the magnitude of the latitude (for departure correction) or departure (for latitude correction) of the side, rather than the total length. It is used when angular measurements are more precise than linear measurements.
3. **Centesimal rule and Reversal point rule:** These are not standard methods for distributing closing errors in a traverse. The centesimal system refers to a unit of angle measurement (grads), and reversal points are related to leveling or specific instrument setups, not error distribution in traverses.
The full form of COD is:
A)
Chemical Oxygen Demand
B)
Chemically Oxygen Demand
C)
Chemistry Oxygen Demand
D)
None of the above
In water quality analysis, COD stands for Chemical Oxygen Demand. It is a critical measure used to determine the amount of oxygen required to chemically oxidize the organic and inorganic matter in a water sample. This is typically achieved using a strong oxidizing agent (such as potassium dichromate) under acidic conditions.
Analysis of options:
- Option (a) 'Chemical Oxygen Demand' is the standard scientific term used globally in environmental engineering and chemistry.
- Option (b) 'Chemically Oxygen Demand' is grammatically incorrect as 'Chemical' (adjective) is required to modify the noun phrase 'Oxygen Demand'.
- Option (c) 'Chemistry Oxygen Demand' is incorrect as 'Chemistry' is the name of the field of study, not the descriptor for the type of demand.
Which of the following is not a geometric controllable parameter of blasting ?
A)
Burden
B)
Spacing
C)
Type of explosive
D)
Hole depth
In blasting engineering, parameters are categorized into geometric (spatial/dimensional) and non-geometric (material/chemical/temporal) parameters.
1. Geometric parameters refer to the physical dimensions and spatial arrangement of the blast holes. These include:
- Burden (the distance from a blast hole to the nearest free face).
- Spacing (the distance between adjacent blast holes in a row).
- Hole depth (the vertical or inclined length of the drilled hole).
- Stemming length and Sub-drilling.
2. Non-geometric parameters refer to the properties of the materials used or the timing of the blast. These include:
- Type of explosive (which determines the velocity of detonation and gas pressure).
- Powder factor (amount of explosive per unit volume of rock).
- Delay timing (the sequence in which holes fire).
Since 'Type of explosive' is a material property and not a spatial dimension, it is not a geometric controllable parameter.
Carbon monoxide has more affinity with haemoglobin than oxygen for about:
A)
2000 times
B)
100 times
C)
210 times
D)
20 times
Carbon monoxide (CO) has a significantly higher affinity for hemoglobin (Hb) than oxygen (O2) does. When CO binds to hemoglobin, it forms carboxyhemoglobin (COHb), which prevents the transport of oxygen to tissues and inhibits the release of any bound oxygen. In toxicology and medical literature, the relative affinity of hemoglobin for CO compared to O2 is generally cited as being between 200 and 250 times greater. Among the given options, '210 times' falls precisely within this scientifically accepted range. Option (a) 2000 times is an exaggeration, while options (b) 100 times and (d) 20 times are too low to account for the extreme toxicity of carbon monoxide even at low atmospheric concentrations.
Which of the following are major environmental issues involved in mining?
A)
Air pollution
B)
Water pollution
C)
Soil degradation
D)
All of the above
Mining activities have comprehensive negative impacts on the environment, affecting air, water, and land.
1. Air Pollution: Mining operations generate significant amounts of particulate matter (dust) from blasting, drilling, and transportation. Additionally, smelting processes associated with mining release sulfur dioxide and other toxic gases into the atmosphere.
2. Water Pollution: Mining often leads to Acid Mine Drainage (AMD), where sulfide minerals are exposed to air and water, creating sulfuric acid that leaches heavy metals into nearby streams and groundwater. Chemical spills from processing plants also contaminate water bodies.
3. Soil Degradation: Open-cast mining involves the removal of topsoil and vegetation (overburden), leading to the complete loss of fertile soil layers, increased soil erosion, and contamination of the land with toxic tailings and chemicals.
Since all three options (a, b, and c) are recognized as major environmental consequences of mining, the correct answer is 'All of the above'.
In emulsion explosive, one of the chemical/ingredient is not included. What is that chemical/ingredient?
A)
Ammonium nitrate
B)
Water
C)
Emulsifying agent
D)
Nitroclycerine
Emulsion explosives are a type of water-in-oil emulsion. Their composition typically consists of: 1) Ammonium Nitrate (the primary oxidizer), 2) Water (used to dissolve the ammonium nitrate), and 3) An emulsifying agent (used to stabilize the mixture of the aqueous oxidizer solution and the fuel/oil phase). Nitroglycerine is the primary ingredient in dynamite (a gelatinous explosive), but it is specifically excluded from emulsion explosives to make them safer to handle, more stable, and less sensitive to accidental detonation. Therefore, Nitroglycerine is not an ingredient in emulsion explosives.
A conveyor transported the coal at the rate of 220 te/hr is 600 m long moving up a gradient of 1 in 60. If the belt width (W) is 0.75 and cross sectional area of the material is 0.1 W2 along with bulk density of coal is 0.8 t/m3. Calculate the belt speed.
A)
0.04 m/s
B)
0.96 m/s
C)
1.36 m/s
D)
1.89 m/s
To calculate the belt speed, we use the fundamental formula for the capacity of a conveyor belt:
Capacity (Q) = Area of material (A) × Velocity (v) × Bulk Density (ρ)
1. **Identify Given Data:**
- Capacity (Q) = 220 tonnes/hr = 220 / 3600 tonnes/sec ≈ 0.06111 t/s
- Belt Width (W) = 0.75 m
- Cross-sectional Area (A) = 0.1 × W² = 0.1 × (0.75)² = 0.1 × 0.5625 = 0.05625 m²
- Bulk Density (ρ) = 0.8 t/m³
- Length (600 m) and Gradient (1 in 60) are provided but are not required for calculating the speed, as speed depends on the throughput and cross-sectional area.
2. **Rearrange the formula to solve for Velocity (v):**
v = Q / (A × ρ)
3. **Substitute the values:**
v = (220 / 3600) / (0.05625 × 0.8)
v = 0.06111 / 0.045
v ≈ 1.358 m/s
4. **Rounding:**
Rounding 1.358 m/s to two decimal places gives 1.36 m/s.
Therefore, the correct option is (c) 1.36 m/s.
The opening cut in opencast mining is called:
A)
Berm
B)
Trench
C)
Drift
D)
Box cut
In opencast (open-pit) mining, the initial excavation made to expose the ore body or coal seam and provide access for machinery is known as a 'Box cut'. It is essentially the first opening cut that allows the mining operation to transition from surface stripping to the development of the pit.
Why other options are incorrect:
- a. Berm: A berm is a horizontal ledge or platform between two benches in an open-pit mine, primarily used for safety (to catch falling rocks) or as a roadway for haulage.
- b. Trench: While a trench is an excavation, in mining terminology, it usually refers to a narrow exploration cut used for sampling or prospecting, not the primary opening cut of a mine.
- c. Drift: A drift is a horizontal underground opening that follows a vein or seam; it is a term associated with underground mining, not opencast mining.
Distance of working from any water body should be at least:
A)
35 m
B)
16.4 m
C)
60 m
D)
48 m
In the context of mining regulations (specifically relating to open-cast mining and safety distances from water bodies), the standard safety requirement to prevent seepage, slope failure, or accidental flooding is typically maintained at 60 meters. This distance acts as a protective barrier or 'buffer zone' to ensure the stability of the mine workings and to prevent the contamination of the water body. While specific regulations can vary slightly by jurisdiction or specific mineral (e.g., Coal vs. Metal), 60m is the recognized standard for general safety distance from water bodies in many technical mining competitive exams based on standard safety guidelines.
Which of the coal have the best heating values in terms of volatile matter?
A)
Containing 20% volatile matter
B)
Containing 30% volatile matter
C)
Containing 40% volatile matter
D)
Containing 50% volatile matter
To determine which coal has the best heating value (Calorific Value) based on volatile matter, we must look at the process of coalification. As coal matures from peat to lignite, bituminous, and finally anthracite, the carbon content increases while the volatile matter (VM) and moisture content decrease.
1. Heating Value and Carbon: The heating value of coal is primarily derived from the combustion of fixed carbon. Higher carbon content generally correlates with a higher heating value.
2. Volatile Matter (VM): Volatile matter consists of gases (like methane) and tars that are released when coal is heated. While VM helps in ignition, an excessively high percentage of VM usually indicates a lower rank of coal (like lignite or sub-bituminous), which also contains more moisture and less fixed carbon.
3. Comparison:
- 50% VM (Option d) and 40% VM (Option c) are characteristic of low-rank coals (Lignite/Sub-bituminous), which have the lowest heating values.
- 30% VM (Option b) is typical of medium-rank bituminous coals.
- 20% VM (Option a) represents a higher rank of coal (High-volatile or Medium-volatile Bituminous moving toward Anthracite).
Since the heating value increases as the rank of coal increases (and volatile matter decreases), the coal with the lowest percentage of volatile matter among the given options will have the highest fixed carbon content and, consequently, the best heating value.
The law which provides that if a given mass of gas (V) is subjected to a change of pressure (P) and temperature (T)at one and same time, then, P1V1/T1 = P2V2/T2, is known as:
A)
Le Chatelier’s equation
B)
Bernoulli’s Theorem
C)
None of these
D)
Graham’s Law
The equation provided, P1V1/T1 = P2V2/T2, is the mathematical expression of the Combined Gas Law. This law combines Boyle's Law (pressure-volume relationship), Charles's Law (temperature-volume relationship), and Gay-Lussac's Law (pressure-temperature relationship) to describe the behavior of a fixed mass of an ideal gas when pressure, volume, and temperature all change simultaneously.
Evaluating the options:
- a. Le Chatelier’s principle relates to chemical equilibrium shifting to counteract a change in conditions; it is not a gas law for P, V, and T.
- b. Bernoulli’s Theorem relates to the conservation of energy in fluid dynamics (pressure, velocity, and elevation), not the state of a gas mass.
- d. Graham’s Law describes the rate of effusion or diffusion of a gas being inversely proportional to the square root of its molar mass.
Since the Combined Gas Law is not listed among the specific named options (a, b, or d), the correct choice is 'None of these'.
In which open stoping method, the stoping operation at lower level is in advance to the upper level?
A)
VCR method
B)
Sublevel method
C)
Room and pillar method
D)
Shrinkage method
In Sublevel Stoping (a variation of open stoping), the orebody is divided into several horizontal sublevels. The stoping operation typically proceeds from the bottom up or involves a sequence where the lower levels are developed and blasted in advance of the upper levels to create a void (stope) into which the blasted ore from the upper levels can fall by gravity. Specifically, in many sublevel open stoping configurations, the lower extraction level is established first to facilitate the removal of ore broken from the sublevels above.
Comparing the options:
- a. VCR (Vertical Crater Retreat) method: This is a top-down method where holes are drilled from the top and blasted in descending slices.
- b. Sublevel method: This is the correct answer as it involves a systematic advance where lower levels are prepared to receive ore from upper levels.
- c. Room and pillar method: This is a horizontal mining method used for flat-lying deposits, not a vertical open stoping method involving upper/lower level sequencing in this manner.
- d. Shrinkage method: In shrinkage stoping, the ore is blasted and left in the stope to act as a working platform; the mining progresses upward, but it is not characterized by the lower level being 'in advance' in the context of open stoping infrastructure.
Find the combined resistance of four parallel airways having individual resistances 64, 4, 64 and 16 Ns2m8 respectively.
A)
2.9 Ns2m8
B)
1.0 Ns2m8
C)
128 Ns2m8
D)
4 Ns2m8
Mine airway parallel: 1/sqrt(R)= sum 1/sqrt(Ri)=0.125+0.5+0.125+0.25=1 => R=1.0.
As per Mohr’s scale of hardness, which rock can be stretched from knife only?
A)
Ortho class
B)
Quartz
C)
Apatite
D)
Diamond
The question refers to Mohs scale of mineral hardness (misspelled as 'Mohr's scale' in the prompt). Mohs scale is a qualitative scale characterizing scratch resistance of various minerals. The scale ranges from 1 (softest) to 10 (hardest).
1. Talc (1)
2. Gypsum (2)
3. Calcite (3)
4. Fluorite (4)
5. Apatite (5)
6. Orthoclase (6)
7. Quartz (7)
8. Topaz (8)
9. Corundum (9)
10. Diamond (10)
In mineralogy, a common field test for hardness is the 'knife test'. A standard steel knife or pocket knife typically has a hardness of approximately 5 to 5.5 on the Mohs scale. Therefore, minerals with a hardness of 5 or less can be scratched (or 'stretched' as per the phrasing in the question) by a knife, while minerals with a hardness of 6 or more cannot.
- Apatite (Hardness 5) can be scratched by a steel knife.
- Orthoclase (Hardness 6), Quartz (Hardness 7), and Diamond (Hardness 10) are all harder than a steel knife and cannot be scratched by one.
In an underground mines, at every place where persons are required to work or pass, the air should not contain:
A)
Less than 19% of O2
B)
More than 19% of O2
C)
More than 0.1% of CO2
D)
All of the above
In underground mine ventilation regulations (such as those outlined in the Coal Mines Regulations or Metalliferous Mines Regulations), the primary objective is to ensure a breathable atmosphere for workers.
1. **Oxygen (O2) Levels**: Normal atmospheric air contains approximately 20.9% oxygen. For safety, regulations specify that the oxygen content in the air at any place where persons work or pass must not fall below a certain threshold to prevent hypoxia. The standard minimum requirement is typically 19%. Therefore, the air should NOT contain 'Less than 19% of O2'.
2. **Carbon Dioxide (CO2) Levels**: While CO2 is a hazardous gas, the limit for its concentration is generally much higher than 0.1%. Most mining regulations set the permissible limit for CO2 at 0.5% (5,000 ppm). Therefore, option (c) is incorrect as 0.1% is too restrictive and not the standard regulatory limit.
3. **Option (b)**: 'More than 19% of O2' is incorrect because having more than 19% oxygen (up to the normal 21%) is desirable and safe; it is the deficiency of oxygen that is the hazard.
Since only option (a) aligns with standard mine safety and ventilation regulations regarding the minimum breathable oxygen level, it is the correct answer.