Which of the following factors does NOT affect mine resistance?

The correct answer is based on the understanding of how resistance is affected in mine ventilation systems. Mine resistance refers to the opposition to airflow, which can be influenced by physical characteristics of the airways through which air moves.

Length of airways directly affects resistance since longer airways create more surface area and obstacles, leading to increased friction and thereby resistance. Similarly, the width of airways plays a significant role; narrower airways restrict airflow and increase resistance due to a smaller cross-sectional area for the air to travel through.

Velocity of air is also crucial, as increased flow rates can lead to greater resistance due to turbulence and increased frictional forces on the airway surfaces.

On the other hand, the color of the air has no impact on mine resistance. The color perceived is due to various factors like contaminants, but it does not affect how air moves through the mine structure or the resistance experienced by airflow. Therefore, this factor does not influence the resistance characteristics in mining airways.