Mine Ventilation and Environmental Hazards - short answer type questions from AMIE exams (Set 2)

Explain homotropal and antitropal ventilation.

  • Homotropal ventilation  Ventilation by a current of air travelling in the same direction as the flow of mineral out of a mine.
  • Antitropal ventilation  Ventilation by a current of air travelling in the opposite direction to that of the flow of mineral out of the mine.

What do you understand by flame-proof apparatus?

  • The equipment is simply contained in a heavy protective enclosure, usually made of die-cast steel, occasionally plastic. If heat or sparks from faulty equipment within the enclosure ignite flammable gas present with it the resulting explosion is contained within the enclosure. 
  • Advantage – simple to design the system, suitable for high power equipment
  • Disadvantage – equipment becomes extremely heavy & expensive; opening the enclosure while powered is not permitted

Name the fittings on an explosion-proof fire stopping.

A fire-stopping should have the following fittings
  • Water gauge,
  • Thermometer,
  • A sampling pipe, 18 mm dia, with a valve for collecting samples of air from behind the stopping.
  • 50 mm dia. mild steel pipe with plug for recording temperature of the atmosphere behind the stopping.
  • Water seal at the floor level for drainage of water. A water seal consists of a piece of pipe built into the brickwork at flow level with a bend at its outbye end which dips into the water contained in a small reservoir.
  • A number plate giving the reference number of the stopping.
  • A signature board for the overman to put his signature and date after inspection of the stopping.

Define geothermic gradient and give its approximate value for Indian coalfields.

The term ‘geo’ means earth, ‘thermal’ means heat and ‘gradient’ means a change in a particular quantity with respect to distance. Thus, we can define ‘geothermal gradient’ as the change of heat/temperature of subsurface rocks with respect to distance.
It is given by the following formula

GG = \frac{{\Delta T}}{{\Delta Z}}{\,^0}C/m
Values in Indian coal mines
Location, Geothermic gradient (m/°C)
Jharia coalfield, India, coal measure rocks, 17.2-39
Raniqanj coalfields, India, coal measure rocks, 38.4
Singareni coalfields, India, coal measure rocks, 30
Kolar Gold Fields, India, 91.1

Define the angle of ‘Yaw' for the anemometer. How does it influence the measurement of airflow?

“Yaw” and angle of yaw” is the angle between the axis of the instrument and the direction of the mean velocity.

What do you understand by water blast?

Water blast cleaning is a technique for cleaning internal and external surfaces, which relies entirely on the sheer force of water from a pressurized source to achieve the desired cleaning effect on the intended surface. Abrasives or toxic chemicals are not used by water blasting systems.s

What do you understand by the term ‘nystagmus'?

Miner's Nystagmus is a vision condition in which the eyes make repetitive, uncontrolled movements. These movements often result in reduced vision and depth perception and can affect balance and coordination. These involuntary eye movements can occur from side to side, up and down, or in a circular pattern.

Define incubation period.

In the extraction of coal underground, the incubation period is customarily used as a tool, for deciding the size of an underground coal mine panel, so that coal therein can be extracted within this period without any sign or symptoms of spontaneous heating. 

Explain why 9.5 per cent methane forms the most dangerous mixture in mine air.

Methane, the main component of natural gas, is combustible, and mixtures of about 5 per cent to 15 per cent in the air are explosive. When the air contains approximately 9.5 per cent of methane (the most dangerous concentration), it reaches the perfect oxidation point, which means that the right amount of fuel is mixing with the right amount of oxygen. This produces water, carbon dioxide and a lot of amount of heat. It does not require much heat to ignite the combustion process and therefore methane explosion can accelerate very fast.

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