JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MINE ENVIRONMENTAL ENGINEERING - II Previous Question Paper (August - 2022 - R16)

Spontaneous heating is the self-heating of coal due to low-temperature oxidation, which can lead to spontaneous combustion if heat dissipation is slower than heat generation. Causes: High susceptibility of coal (high moisture and volatile matter), presence of pyrite, geological disturbances like faults, presence of crushed coal in goaf areas, and inadequate ventilation leading to leakage of air through coal pillars or goaf. Detection: Monitoring of mine air for indicators such as carbon monoxide (CO), the Graham's ratio (CO/O2 deficiency), ethylene (C2H4), and hydrogen (H2). Physical signs include an increase in air temperature, sweating on roof or sides, and the smell of oil or smoke. Precaution: Minimizing air leakage through proper ventilation control, using pressure balancing techniques, sealing off abandoned areas with fire-resistant stoppings, adopting depillaring methods that minimize coal loss, and applying fire-retardant coatings on exposed coal surfaces.

Open fires in mines are detected through a combination of direct observation, environmental monitoring, and sensory indicators. Visual and Sensory Detection: Direct observation of flames or glowing embers, presence of thick smoke, and the smell of burning materials (wood, oil, or rubber). Environmental Monitoring: Continuous monitoring of atmospheric gases is critical. Rapid increases in carbon monoxide (CO) concentrations, often accompanied by a significant drop in oxygen levels, are primary indicators. Thermal Detection: The use of infrared thermography and handheld thermal imaging cameras helps identify localized hotspots on conveyor belts, electrical equipment, or coal faces before visible flames occur. Fire Detection Systems: Installation of point-type smoke detectors, linear heat sensors along conveyor galleries, and flame detectors in high-risk areas like substations and workshops provide early warning signals to the surface control room.