What is the primary function of an overcast in mine ventilation?

The primary function of an overcast in mine ventilation is to enable one air current to cross another without mixing. This is crucial in mining operations, as it allows for the effective separation of different airflows that serve distinct purposes, such as maintaining fresh air supply and removing contaminated air. By ensuring that two air currents can cross without mixing, an overcast helps to optimize air quality and reduce the risk of hazardous conditions, such as the accumulation of harmful gases. This highly controlled airflow arrangement is essential for maintaining safe and healthy working conditions within the mine.