Jawaharlal Nehru Technological University Hyderabad B.Tech III MINE ENVIRONMENTAL ENGINEERING - II Previous Question Paper (February - 2022 - R18)

Spontaneous combustion in coal mines is primarily caused by the low-temperature oxidation of coal when it reacts with oxygen in the air. This chemical process is exothermic, and if the heat generated exceeds the rate of heat dissipation, the temperature of the coal mass rises, leading to an exponential increase in the reaction rate. Factors contributing to this include the rank and moisture content of the coal, the presence of pyrites, the degree of coal fragmentation, and the availability of oxygen through leakage in ventilation systems.

Mine fires are broadly classified into two categories based on their origin and development: endogenous fires and exogenous fires.

1. Endogenous Fires (Spontaneous Combustion): These fires originate from within the coal seam due to self-heating. The process begins with the absorption of oxygen by coal, leading to oxidation. Key characteristics include:

• Induction Period: The time taken for coal to reach its ignition temperature under specific conditions.
• Factors: High volatile matter, presence of moisture, and geological factors like faulting or crushing of coal increase susceptibility.
• Detection: Often identified by the smell of oil or smoke, sweating on coal surfaces, or the presence of carbon monoxide (CO) in the return air.

2. Exogenous Fires: These fires are caused by external sources of ignition introduced into the mine environment. They are typically sudden and require immediate suppression. Common causes include:

• Electrical Faults: Short circuits, overheating of cables, or sparks from electrical equipment.
• Mechanical Friction: Overheating of conveyor belt rollers, bearings, or friction between moving parts and coal/timber.
• Blasting Operations: Improper use of explosives or ignition of methane gas by sparks during blasting.
• Human Negligence: Use of open flames, smoking, or improper handling of welding and cutting equipment underground.

While endogenous fires are characterized by a slow, smoldering development that is difficult to locate, exogenous fires are usually open flames that spread rapidly through combustible materials like timber supports, conveyor belts, and hydraulic fluids. Management strategies for both involve strict ventilation control, regular monitoring of atmospheric gases, and the use of fire-fighting equipment such as fire extinguishers, stone dust barriers, and inert gas injection.