Mine Ventilation & Air Conditi

Cheatsheet Content

### Introduction to Mine Ventilation Mine ventilation is crucial for maintaining safe and healthy working conditions in underground mines. It involves controlling air quality, temperature, and humidity, and removing harmful gases and dust. #### Key Aspects - **Air Quality Control**: Ensuring breathable air by removing pollutants. - **Thermal Environment**: Managing heat and humidity for miner comfort and safety. - **Dust Control**: Mitigating the physiological effects of mine dust. - **Methane Drainage**: Preventing explosions and utilizing methane as a resource. ### Effect of Heat and Humidity on Miners Miners' health and efficiency are significantly impacted by the thermal environment. #### Metabolic Heat Balance - **Metabolic Energy (M)**: Energy from food oxidation ($$M = Metabolic Heat + Work_{gravity} + Stored Energy (Ac)$$). - **Heat Transfer**: - **Convection & Radiation**: Primary modes of sensible heat transfer. - **Evaporation**: Main mechanism for heat removal from the human body (sweat). - **Body Temperature Regulation**: - **Central Core Body Temperature ($$T_c$$)**: Maintained at 36.9°C (normal range 35.9-37.9°C). - **Mean Skin Temperature ($$T_{sk}$$)**: Lower than $$T_c$$. - **Blood**: Acts as a cooling agent for the skin. #### Thermal Conditions & Health Impacts - **Hypothermia**: Body temperature falls below 36°C (heat loss > heat production). - **Effects**: Heart rate slows, blood vessels constrict, shivering, hypothermia, potentially death. - **Hyperthermia**: Body temperature rises above 37.9°C (heat production > heat loss). - **Effects**: Body temperature increases, reduced heat removal. #### Dry Bulb Temperature Effects | Dry Bulb Temp (°C) | Body Temp (°C) | Physiological Effects | |--------------------|----------------|-----------------------| | 36.9 | 36.9 | Heat transfer reverses, heat removal only via evaporation | | --- | 39 | Heart beat > 140 bpm, fatal | | --- | 41 | Unconsciousness, coma, potential death | | --- | > 43.3 | Sudden death | #### High Wet Bulb Temperature Effects - High relative humidity hinders evaporation. - Body temperature rises if evaporation is reduced. - If body temperature exceeds 2°C rise, heart rate increases, leading to unconsciousness or death. | Wet-bulb Temp (K) | Rise in Body Temp (K) | |-------------------|-----------------------| | = 307.65 | 1.44-1.90 | #### Heat Hazards - **Heat Cramps**: Caused by prolonged exposure to high temperatures, heavy perspiration, and salt loss. - **Symptoms**: Severe muscle cramps, exhaustion, dizziness. - **Care**: Cool place, salted water, massage, ice packs. - **Heat Exhaustion**: Due to excessive heat exposure and loss of fluid/salt. Can lead to heat stroke. - **Symptoms**: Rapid/shallow breathing, cold/clammy skin, dizziness, heavy perspiration, weak pulse. - **Care**: Cool place, rest, remove clothes, fan skin, salted water, oxygen if needed. - **Heat Stroke**: Body fails to regulate temperature, especially above 41°C. Fatal. - **Symptoms**: Deep/shallow breathing, rapid/weak pulse, dry/hot skin, dilated pupils, loss of consciousness. - **Care**: Immediate cooling, dark room, oxygen, ice packs, urgent medical attention. #### Air Velocity Effects - **Higher air velocity**: Aids evaporative cooling. - **1 m/s**: Good comfort. - **> 2 m/s**: Causes dust, discomfort. - **3 m/s + High Dry Bulb Temp (48.85°C) + Low Relative Humidity**: Causes burning sensation, rise in body temperature, potentially heat stroke. #### Miners' Working Efficiency - Efficiency decreases with rising temperature and relative humidity. - Initial drop is gentle, becomes steeper as wet bulb temperature increases. ### Heat Indices in Underground Mines Heat indices quantify the degree of comfort based on environmental factors. #### Direct Indices - **Wet-bulb temperature (aspirated)**: Most important for hot and humid conditions; reliable when evaporation is dominant. - **Standard**: 2.5-3.0 m/s can raise dust. - **Dry-bulb temperature**: Rare as a standalone index. Useful with air velocity when convection/radiation dominate. - **Limitation**: Above 45°C causes burning sensation. #### Empirical Indices (Kata Thermometer) - **Developed by Dr. L. Hill (1916)**. - **Construction**: Glass thermometer with a large bulb, two smaller bulbs, and alcohol as thermometric fluid. Marks at 35°C (95°F) and 37.8°C (100°F). - **Working**: - **Dry-kata**: Measures heat loss by convection and radiation. - **Wet-kata**: Measures heat loss by convection, radiation, and evaporation. - **Kata Cooling Factor**: Heat lost (millicalories) per cm² of bulb surface cooling from 37.8°C to 35°C. #### Numerical Approach (Wet-Kata Cooling Power) - **Mishra (1986)**: - $$K = (14.65 + 35.59v^{1/3})(309.65 - T_w)$$ for $$v \le 1$$ m/s - $$K = (4.19 + 46.05v^{1/3})(309.65 - T_w)$$ for $$v \ge 1$$ m/s - Where: $$K$$ = kata cooling power (W/m²), $$v$$ = air velocity (m/s), $$T_w$$ = wet bulb temperature (K). - **McPherson (1993)**: - $$K = (0.7 + v^{0.5})(36.5 - T_w)$$ - Where: $$K$$ = wet kata cooling power (mcal/(cm² S)), $$T_w$$= wet-bulb temperature (°C), $$v$$ = air current velocity (m/s). - **Standards**: - Preferred: 4.5-12.0 mcal/(cm² s). - Light work: 4.5 mcal/(cm² s). - Moderate work: 7 mcal/(cm² s). - Hard work: 12 mcal/(cm² s). #### Limitations of Kata Thermometer - Variation of kata factor with temperature. - Underestimates temperature and humidity effects, overestimates air velocity effects. - Cools faster than human body due to different convective/evaporative coefficients and smaller volume to surface area ratio. - A comfortable environment of 165 W/m² requires a kata reading of 5 x 165 W/m² due to faster cooling. - Fragile bulb. - Limited use in hot and humid climates. #### Rationally Derived Indices - **Human Body Heat Balance**: $$M = W + Ac + (Rad + Con + Evp + Br)$$ - For steady state, $$Ac = 0$$. Breathing heat loss (Br) is negligible. - $$M - W = Rad + Con + Evp$$ (Cooling power of the environment). - **Factors affecting Cooling Power**: - Wet bulb temperature ($$T_w$$) - Dry bulb temperature ($$T_d$$) - Mean radiant temperature ($$T_r$$) - Air-current velocity ($$v$$) - Atmospheric pressure ($$P_a$$) - Skin temperature ($$T_{sk}$$) - Wetted area fraction ($$w_a$$) ### Humidity and Hygrometers Understanding and measuring humidity is vital for mine ventilation. #### Humidity Definitions - **Humidity**: Water-vapor content of air. Moist air is common in mines. - **Capacity to hold moisture**: Increases with temperature. - **Relative Humidity (RH)**: Ratio of vapor pressure to saturation vapor pressure at the dry bulb temperature. - $$RH = (e / e_{sd}) \times 100\%$$ - Unitless, expressed as percentage. - **Specific Humidity**: Weight (kg) of water vapor per kg of dry air. - $$Specific Humidity = 0.622 \times (e / (P_b - e)) kg/kg_{dry air}$$ - Where: $$e$$ = vapor pressure (kPa), $$P_b$$ = barometric pressure (kPa). - **Absolute Humidity**: Amount of water vapor (kg) per unit volume of air (m³). - $$m' = (10^3 e) / (461.9T)$$ - Where: $$m'$$ = absolute humidity (kg/m³), $$T$$ = temperature (K). - **Discouraged**: Varies with temperature and pressure changes in ventilation system. - **Dew Point**: Temperature at which air becomes saturated, leading to condensation. - At dew point: dry bulb and wet bulb temperatures are equal, RH = 100%. - **Degree of Saturation**: Ratio of weight of water vapor in air to weight of water vapor in saturated air (at constant temperature). - $$Degree of Saturation = (0.622 \times (e / (P_b - e))) / (0.622 \times (e_{sw} / (P_b - e_{sw}))) \times 100\%$$ - Where: $$e_{sw}$$ = saturation vapor pressure at wet bulb temperature (kPa). #### Vapour Pressure (e) - **Dalton's Law**: Total pressure ($$P_b$$) = partial pressure of dry air ($$P_d$$) + vapor pressure ($$e$$). ($$P_b = P_d + e$$). - **Calculation**: $$e = e_{sw} - 0.000644 P_b (T_d - T_w)$$ - Where: $$e_{sw}$$ = saturation vapor pressure at wet bulb temperature (kPa), $$P_b$$ = barometric pressure (kPa), $$T_d$$ = dry bulb temperature (°C), $$T_w$$ = wet bulb temperature (°C). - **Saturation Vapour Pressure ($$e_s$$)**: Maximum water vapor air can hold at a specific temperature. - $$e_s = 610.6 \exp (17.27T / (237.3 + T)) Pa$$ - Independent of pressure, increases with temperature. #### Methods of Measuring Water Vapour Content | S.No. | Method | Apparatus/Instruments Used | |-------|--------------------------|-----------------------------------------| | 1. | Thermodynamic method | Psychrometers | | 2. | Using hygroscopic substances | Hair hygrometers | | 3. | Condensation method | Dew-point hygrometers | | 4. | Absorption method | - | | | a. Chemical method | - | | | b. Electrical methods | Electronic psychrometers or humidity meters | #### Hygrometers (Thermodynamic Method) - **Wall Mounted Type**: Non-ventilated, fixed in well-ventilated mine areas. - **Construction**: Two thermometers (dry/wet bulb), wet bulb covered by muslin cloth immersed in water. - **Working**: Records dry and wet bulb temperatures, barometric pressure. - **Precautions**: Avoid nearby heat sources, wipe bulbs, use distilled water. - **Whirling Hygrometer (Sling Psychrometer)**: Rotated to create air current. - **Construction**: Wooden frame with handle, two thermometers (dry/wet bulb), wet bulb covered by muslin cloth with water supply. - **Working**: Rotated at ~200 rpm for 1-2 minutes for steady reading. Water evaporation cools wet bulb. - **Precautions**: Keep away from observer's body, record wet-bulb first (fluctuates). - **Limitations**: Moisture affects thermometers without sufficient air current (>3 m/s). - **Aspirated Type (Assmann Psychrometer)**: Fan-driven for accurate readings. - **Construction**: Two thermometers (dry/wet bulb), battery-driven fan, metal sleeves (chromium-coated) for bulbs, central tube for insulation. - **Working**: Fan draws air through inner sleeves, air travels through central tube, exits via slits. Fan runs ~3 minutes for constant wet-bulb temp. - **Advantages**: High accuracy (± 1%), shields from radiation, accurate in sunlit areas, easy to operate. - **Precautions**: Requires calibration, hold away from observer, hold opposite to airflow direction. #### Calculating Water Vapour Content 1. **Record/Measure**: $$T_d$$ (dry bulb temp), $$T_w$$ (wet bulb temp), $$P_b$$ (barometric pressure). 2. **Evaluate $$e_s$$**: $$e_s = 610.6 \exp (17.27T / (237.3 + T)) Pa$$ (replace $$T$$ with $$T_d$$ for $$e_{sd}$$ and $$T_w$$ for $$e_{sw}$$). 3. **Evaluate $$e$$**: $$e = e_{sw} - 0.000644 P_b (T_d - T_w)$$ 4. **Calculate Specific Humidity**: $$0.622 \times e / (P_b - e) kg/kg_{dry air}$$ 5. **Calculate Relative Humidity**: $$(e / e_{sd}) \times 100\%$$ ### Sources of Heat in Mines Heat sources contribute to adverse thermal conditions in underground mines. #### Major Sources - **Strata Heat**: Heat from the surrounding rock mass. - **Auto-compression**: Air warms up as it flows deeper into the mine due to compression. - **Machinery and Lights**: Heat generated by equipment and lighting. - **Underground Water**: Warm water bodies. #### Minor Sources - **Human Metabolism**: Heat generated by workers. - **Oxidation**: Chemical reactions (e.g., coal oxidation). - **Blasting**: Heat released during explosive operations. - **Rock Movement**: Frictional heat from ground movement. - **Pipelines**: Heat transfer from pipes carrying fluids. - **Energy Losses in Airflow**: Frictional losses. #### Air Conditioning Necessity - When temperature and humidity exceed limits, air conditioning (refrigeration plants, spot coolers) is required to ensure comfort, safety, and efficiency. - In extreme cold climates, heat may need to be supplied to intake air. ### Methods of Improving Cooling Power of Mine Air Various techniques are employed to enhance the cooling capacity of mine air. #### 1. Increasing Quantity of Ventilating Air - **First Option**: Improves hot and humid conditions. - **Mechanism**: Dilutes heat, increases air velocity (improves cooling power). - **Deep Mines**: Requires extra air to deal with heat. - **Heat Balance**: $$M H_a = q + M H_i$$ or $$Q = q / ((H_a - H_i) \rho)$$ - Where: $$q$$ = heat added (kW), $$M$$ = mass flow-rate of dry air (kg/s), $$Q$$ = air flow (m³/s), $$\rho$$ = apparent density (kg/m³), $$H_a$$ = allowable enthalpy (kJ/kg), $$H_i$$ = in-flowing air enthalpy (kJ/kg). - **Limitations**: - **Mine airways**: Must be large enough to handle increased air quantity without excessive frictional pressure loss or velocity. - **High pressure loss**: Increases ventilation power cost. - **High velocity**: Raises dust. #### 2. Circulating Drier Air - **Importance**: Maintaining dry air in deep, hot mines improves working conditions. - **Drying Methods**: - **Refrigeration**: Most economical for drying. - **Desiccants**: Calcium chloride, magnesium chloride, silica gel (costly, heat of absorption counteracts drying). - **Preventing Moisture Pickup**: - **Dry mining**: Prevent water evaporation from strata. - **Dust-collecting means**: Adopt dry methods over water for dust suppression in hot mines. - **Spraying fuel oil**: Reduces evaporation from airways. - **Concrete lining**: In major airways. - **Drain pipes**: To remove water behind lining. - **Covering water drains**: Minimizes evaporation. #### 3. Cooling or Refrigeration of Circulating Air - **Necessity**: When increasing air quantity is insufficient. - **Process**: Air cooled and dehumidified by refrigeration plants (275-278 K), then directed to working faces. - **Design**: Plant capacity sufficient for the farthest face. #### Calculation of Cooling Load - If total heat added ($$q$$), required cooling load ($$q_c$$) is: - $$q_c = q + Q \rho (H_i - H_a)$$ kW - **Cooling load**: Calculated for maximum heat content of in-flowing air (summer). #### Refrigeration Methods - **Freezing Mixture**: Ice and salt (NaCl, CaCl2). Latent heat for freezing taken from mixture. Liquid mixture cools other substances. - **Dry Ice**: Solid carbon dioxide. Sublimes at -78°C, no liquid residue. Expensive. - **Refrigerants**: Volatile liquids used in refrigerating machines. - **Ideal Refrigerant**: Low boiling point (~0°C), non-corrosive, high heat transfer efficiency, non-toxic. - **Common Refrigerants**: | Name | Chemical Formula | Boiling Point (°C) | Absolute Saturation Pressure (bar) at 5°C | Absolute Saturation Pressure (bar) at 50°C | Limitations | |-------------------|------------------|--------------------|--------------------------------------------|--------------------------------------------|----------------------------------| | Refrigerant 717 | NH3 | -33.4 | 5.16 | 20.3 | Toxic nature | | Refrigerant 11 | CCl3F | +23.9 | 0.49 | 2.35 | By-products deplete ozone layer | | Refrigerant 12 | CCl2F2 | -30 | 3.62 | 12.2 | By-products deplete ozone layer | #### Refrigeration Systems - **Absorption System** - **Compression System**: Commonly used (vapor compression type). Liquid refrigerant extracts latent heat of vaporization from mine air. #### Vapor Refrigeration Cycle Components - **Evaporator**: Refrigerant "boils" (evaporates), absorbing heat. - **Compressor**: Compresses vaporized refrigerant. - **Condenser**: Vapor condenses to liquid, releasing heat. - **Expansion Valve**: Refrigerant expands, temperature and pressure drop. #### Classification of Refrigeration Plants (by location) 1. **Surface Plant**: - **Mechanism**: Air cooled on surface, then sent underground via intake shaft. - **Advantages**: Simplicity, lower cost (cheaper refrigerants), ease of operation/inspection, easy waste heat disposal, aids natural ventilation pressure. - **Disadvantages**: Poor positional efficiency, cooled air picks up heat due to auto-compression in deep shafts. - **Example**: Champion Reef Gold mine (Kolar Gold Field, 1940s) - 3.7 MW capacity, ammonia refrigerant, reciprocating compressors, cooling water pumps, shell and tube condenser. - **Working**: Ammonia compressed, oil separated, cooled to liquid in condenser (water circulated by pumps). Liquid ammonia passed to shell-and-tube evaporator, exchanging heat with calcium chloride solution (to cool mine air). Liquid ammonia converts to gas, sent to compressor. - **Cooling capacity**: 70.8 m³/s of air cooled from 21.1°C DBT / 18.3°C WBT to 4.4°C saturated. 2. **Underground Plant**: - **Mechanism**: Cooling plant located underground. Air cooled centrally or at chilled water spray chambers near face. - **Advantages**: High positional efficiency, avoids auto-compression heating, no surface pipe ranges/pumping costs, avoids environmental problems of surface plants. - **Disadvantages**: Higher refrigerant cost (non-toxic needed), difficult heat dissipation, frequent cleaning due to dust, small capacity (up to 1.75 MW). - **Example**: Champion Reef Mine (80th level) - cooled intake air 2318m below surface. 3 cylinder 125 h.p. reciprocating compressors, Freon 12 refrigerant. 30kW pump, 51m head. Condensing water cooled in upcast shaft. - **Cooling capacity**: 9.44 m³/s of air cooled from 32.75°C DBT / 20.05°C WBT to 3.35°C saturated. 3. **Spot Coolers**: - **Mechanism**: Small, semi-portable refrigerating units for isolated hot workings (50-500 kW). - **Types**: - **Small spot coolers**: Direct cooling of air stream on evaporator coils (refrigerant evaporation). - **Big spot coolers**: Use intermediate coolant (e.g., water). - **Advantages**: Maximum positional efficiency, aids dust suppression, compact, effective in deep mines. - **Disadvantages**: Leaves rest of mine air hot, very expensive. - **Example**: Champion Reef, KGF (102nd level) - 140 kW capacity, R12 refrigerant, 6.37 m³/s air cooled from 41.6°C DBT / 25.8°C WBT to 33.3°C DBT / 22.2°C WBT. #### 4. Regenerative Cooling - **Theoretical Concept**: Not yet adopted in practice. - **Mechanism**: High density, low specific heat gas (e.g., CO2) circulated in a closed circuit (down upcast shaft, up downcast shaft). Heat from auto-compression dissipated into upcast air. Cooling from auto-expansion cools downcast air. - **Benefits**: Cools downcast air, increases natural ventilation. #### 5. Using Devaporized Compressed Air - **Mechanism**: Air compressed (500-650 kPa), cooled in heat exchanger (devaporized compressed air stream), then used to run an air motor. Expansion cools air to 273 K, liquefying and removing moisture. - **Benefits**: Dry air helps maintain temperature and humidity at the face. ### Mine Gases – Methane (CH4) Methane drainage is critical for safety and can provide a valuable fuel source. #### Methane Drainage - **Purpose**: Reduces CH4 emissions, minimizes hazards, and provides fuel. - **Fuel Value**: 1 kg CH4 evolves 13,600 kcal (vs. 580 kcal for gunpowder, 1500 kcal for nitroglycerine). - **Application**: Recommended for seams with gas emission > 20-25 m³/t. - **History**: First tried in Ruhr coalfields (Germany, 1943). Experimented in India (Amlabad colliery). - **Degasification**: - From the seam being worked. - From seams above or below the working seam. #### Methods of Methane Drainage - **No Single Preferred Technique**: Choice depends on permeability, drainage reason, and mining method. 1. **In-seam Drainage**: - **Conditions**: Successful if coal permeability is high. - **Mechanism**: Boreholes drilled into the seam (up to 1000m length, 100mm diameter initially, then 75mm) from return airways, connected to pipe system. Pre-drains seam before working. - **Spacing**: 10-80m, depending on permeability. - **Flanking Boreholes**: Drain gas from coal ahead of advancing headings. - **Life Cycle**: - **Initial High Flow**: Due to gas expansion and desorption. - **Dewatering Phase**: Permeability increases, gas flow increases. - **Depletion Phase**: Gas flow decays as zone is depleted. - **Dewatering**: Removes water from boreholes to improve methane flow and enhance strata permeability. Inner pipe for water, outer for methane. - **Challenges**: Spalling of coal (use smooth drill rods), drill chippings (use water flush/augers). - **Maintenance**: Perforated plastic liners maintain open holes. 2. **Gob Drainage by Surface Boreholes**: - **Purpose**: Captures "gob gas" (methane in caved longwall goaves) to prevent migration into working areas. - **Mechanism**: Vertical boreholes drilled from surface (500-600m intervals along panel centerline). - **Borehole Specs**: 200-250mm diameter, drilled 8-10m into roof of coal seam. Cased near surface. - **Activation**: Methane accumulates as face passes under borehole. - **Yield**: Can yield > 50,000 m³/day for months. - **Application**: Favored in the United States, also used in pillar extraction areas. - **Control**: Surface gas drainage pumps control flow rate and gas purity. Excessive suction draws ventilating air, diluting methane. 3. **Cross-measure Borehole Method**: - **Common Method**: Used when surface drilling is difficult. - **Mechanism**: Boreholes drilled from roadways in working seams at an inclination (50-60° in flat seams), either upwards or downwards (upward preferred). - **Hole Specs**: 65-90mm diameter, 15-100m length (30-45m preferred), spaced 20-30m apart (zones overlap slightly). - **Suction**: 1000-1500 Pa. - **Preparation**: Sand and water injected at high pressure to break open strata pores. - **Efficiency**: 20-70%. 4. **Superjacent or Hirschbach Method**: - **Applicability**: Unworkable seam 25-35m above working seam. - **Mechanism**: Headings (5-7m² cross-section) driven 25-30m above working seam, positioned midway between gate roads. - **Benefits**: Maximum gas quantity with high methane percentage, avoids interference with mining operations. Suitable for retreating longwall and bord-and-pillar. - **Limitations**: Not successful with massive sandstone caps (poor roof fissures). - **Practice**: Both along-the-seam and cross-measure boreholes drilled from headings. Headings sealed at outbye end. Methane drawn with 203 kPa suction. - **Prevalence**: Eastern Europe and China. 5. **Pack-cavity Method**: - **Mechanism**: Corridors or webs left in solid pack (40m intervals, 20m from intake/return-gate roads), connected to main pipe range in return airway. Gas collected with 250-350 Pa suction. - **Pipe Specs**: Individual pack cavities connected to 150-300mm diameter main pipe range. - **Disadvantages**: Minimum gas quantity, often diluted. Small, closely controlled suction head needed to prevent air leakage and spontaneous heating. ### Mine Dust – Physiological Effects and Control Mine dust poses significant health and safety risks to workers. #### Introduction to Aerosols - **Natural Atmosphere**: Contains liquid and solid particles (aerosols). - **Aerosol**: Solid or liquid particles suspended in a gas. - **Sources**: Natural (volcanic activity, soils) and industrial (condensation, smokes). - **Visibility**: Most particles are invisible. - **Common Forms**: Dust, fumes, smoke, fog, smog, haze. #### Dust - **Definition**: Solid particulate matter suspended in gas. - **Problem**: Most common aerosol problem in mineral industries. - **Formation**: Fragmentation processes (drilling, crushing, grinding, air movement). - **Particle Size**: 1-100 µm. - ** 20 µm**: Settle quickly. #### Fumes - **Definition**: Solid products from combustion, sublimation, or distillation. - **Particle Size**: 10 µm captured before larynx. - **Mouth Breathing**: Bypasses initial protection. - **Trachea/Bronchioles**: Air progresses through. Trachea (20mm diameter, 120mm long) composed of cartilage rings. Passages subdivide like tree roots. - **Air Velocity**: Decreases to laminar flow in smaller bronchioles. - **Mucus**: Coats passages, continuously expelled. Bronchial ailments can increase mucus viscosity/thickness, restricting airflow. - **Higher Air Velocities (wheezing)**: Through constricted passages can cause audible noise. - **Alveoli (air sacs)**: Smallest bronchioles terminate here (0.2-0.6mm). Walls are 0.5 µm thick membrane for gas exchange. - **Dust Retention**: - Few particles > 3 µm reach alveoli. - 0.2 µm particles: 25% retention. - 0.02 µm particles: ~55% retention. - **Mucus Production**: Cells lubricate alveoli, facilitate dilation/contraction. - **Dust Removal from Alveoli**: - **Macrophages (phagocytes)**: Large cells (10-50 µm) engulf particles up to 10 µm. Migrate to bronchioles for ciliary expulsion. - **Life Expectancy of Macrophage**: ~1 month. Rapid death if toxic particles engulfed. - **Increased Dust**: Increases macrophages, but dust-loaded cells cleared slower. - **Soluble Particles**: Dissolve in mucus or diffuse through epithelium into bloodstream. #### Mine Dust Diseases 1. **Pneumoconiosis (Black Lung)**: Generic term for cardiorespiratory damage from dust inhalation. - **Coal Workers' Pneumoconiosis (CWP)**: - **Cause**: Coal dust. Low biological response. - **Progression**: Dust accumulation forms soft plaques in lung tissue (small black spots on X-rays). - **Diagnosis**: 10-15 years after employment. - **Advanced Stages**: Opacities grow, coalesce, accompanied by fibrosis. - **Symptoms**: Cough, shortness of breath, chest tightness, black sputum (mucus). May occur at rest in advanced stages. - **Severe**: Scarring prevents oxygen reaching blood, stressing heart/brain, causing additional symptoms. - **Treatment**: No cure. Slow progression: maintain weight/nutrition, exercise, prevent infections. - **Prevention**: Black lung is preventable. 2. **Silicosis**: - **Cause**: Free crystalline silica (quartz, chert). Not silicates in clays. - **Hazard**: Greatest from freshly produced dust (mining, sandblasting). Progressive and fatal. - **Progression**: - **Early Stages**: Localized dust accumulations (X-ray). - **Advanced**: Progressive massive fibrosis. - **Types**: - **Chronic**: > 10 years exposure. Simple silicosis, progressive massive fibrosis. - **Subacute (Accelerated)**: 2-5 years exposure, heavier exposure. - **Acute**: Few months of intense exposure to high percentage silica. 3. **Asbestosis**: - **Cause**: Inhalation of asbestos (inorganic mineral fiber, silicate chains). - **Types**: Chrysotile (curly fibers), Amphibole (straight, brittle fibers). - **Mechanism**: Fibers captured in respiratory system (interception), accumulate at bends/bifurcations. Aerodynamic diameter determines reach to alveoli. - **Effects**: Fibrosis (different from silicosis/CWP), brittle plaques with sharp calcified ridges. Fibrous bands radiate through lungs, significant loss of elasticity. - **Physiological Impact**: Reduced tidal volume, breathlessness. Reduced oxygen transfer stresses heart, leading to cardiac failure. - **Cancer Link**: Linked to bronchial, lung, abdominal cancers. Carcinogens adsorbed on fiber surfaces (not silicate chains themselves). ### Other Indirect Ways of Controlling Mine Climate - **Acclimatization**: Allowing workers to adapt to hot conditions. - **Control of Moisture**: Preventing excessive humidity. - **Proper Ventilation System**: Ensuring efficient air circulation.