What is Main Fall:
When the area of extraction or void area is nearly eqal to or more than the square of the depth,the cracks due to depillaring extend up to surface.The rooffall which affected the surface is known as"Main fall".The main fall take place long after the first roof fall or localfall in the depillaring district.If the seam is at a shallow depth the air leaks through the cracks which is developed due to main fall and is responsible for spontaneous heating.Such spontaneous heating hass been the case of fire in the area near Jharia and Katras town.

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