Why in the mine ventilation system, when conditions permit, try to divide the total intake air early and converge the total return air late?

Each mine must have a complete independent ventilation system, and it is not appropriate to combine two mines that can be ventilated independently into one ventilation system.

If there are two air shafts, the airflow from the mining area to each air shaft should be independent.

Before the return air of each working face enters the return air duct of the mining area, the return air of each mining area cannot be arbitrarily penetrated before entering the return air level, and the lower level return air flow and the upper level intake air flow must be strictly separated.

When conditions permit, try to separate the total inlet air early and converge the total return air late.