What is not permitted in areas with multiple fans?

In underground mining operations where multiple fans are installed to ventilate the area, it is crucial that airflow is managed efficiently to ensure the safety and health of miners. Neutral areas, which are zones where there is little to no airflow or where the airflow is substantially weakened, can be problematic in such environments. These areas might not provide adequate ventilation and can lead to the buildup of hazardous gases or insufficient oxygen levels.

Having multiple fans can create overlapping air currents, which, while needing to be balanced correctly, do not necessarily create neutral areas and can provide effective ventilation. Excessive noise from fans is an issue but does not directly impact the safety of airflow management. High air pressure might be a consideration in certain contexts but does not apply directly to conditions leading to neutral zones. Thus, neutral areas are distinctly undesirable because they undermine the purpose of having a well-ventilated space, making them not permitted in areas with multiple fans.