What are the two systems of ventilation used in mines?

The correct choice identifies blowing and exhaust as two systems of ventilation used in mines, which is an important concept in mining operations.

Blowing refers to the method where fresh air is introduced into the mine to dilute and remove harmful gases, dust, and heat, ensuring a safe breathing environment for miners. This system uses fans or blowers to push air into the mine workings.

Exhaust, on the other hand, involves the removal of contaminated air from the mine. This can be achieved through shafts or ventilation ducts that help displace the stale air with fresh air drawn from the surface. Exhaust systems are crucial for maintaining air quality and preventing the accumulation of hazardous gases.

Understanding these ventilation systems is vital for mine safety management, as they directly relate to preserving air quality and minimizing health risks associated with mining operations. In contrast, the other options refer to different concepts that do not specifically delineate the primary systems of ventilation used in mining environments.