Surface Environment, Mine Ventilation and Underground Hazards
This section tests airflow in mine roadways and networks, ventilation planning and fans, mine gases and dust, and the hazards of fire, explosion and inundation. It is the most formula-driven part of the paper: almost every calculation reduces to Atkinson's equation, network reduction, or fan power and fan laws.
Ventilation principles
- Atkinson: pressure drop p = R Q^2, with resistance R = k C L / A^3 for a roadway.
- Networks: resistances add in series; in parallel the reciprocals of square roots add, 1/sqrt(R_eq) = sum of 1/sqrt(R_i).
- Natural ventilation pressure arises from the density difference between intake and return columns, approximately (rho1 - rho2) g H.
- Fan air power = p x Q; shaft power = p x Q / efficiency. Fan laws: Q scales with speed N, pressure with N^2, power with N^3.
Gases, dust and hazards
- Methane is explosive between about 5 and 15 percent in air; carbon monoxide is dangerous well below 0.1 percent; carbon dioxide (blackdamp) collects at the floor.
- Coal dust explosions are suppressed by stone-dusting to raise the incombustible content and by water barriers; spontaneous combustion is tracked by gas ratios and crossing-point methods.
- Dust sampling is gravimetric or konimeter-based; heat stress uses kata thermometer, WBGT and air cooling power.
Worked example
Two parallel airways have resistances R1 = 0.4 and R2 = 0.9 Ns^2/m^8. 1/sqrt(R_eq) = 1/sqrt(0.4) + 1/sqrt(0.9) = 1.581 + 1.054 = 2.635. sqrt(R_eq) = 0.3795, so R_eq = 0.144 Ns^2/m^8. For a total airflow of 60 m^3/s, p = 0.144 x 60^2 = 518.4 Pa, and the fan shaft power at 75 percent efficiency is 518.4 x 60 / 0.75 = 41.5 kW.
Traps
- Adding parallel resistances directly instead of adding reciprocals of square roots.
- Assuming the total airflow splits equally between parallel branches; it splits inversely with the square root of resistance.
- Applying the fan laws with power proportional to N^2 rather than N^3.