Disintegration of the immediate shale roof in coal mines interferes with ventilation, production, and safety. The effect is seasonal and correlates with high levels of moisture in the intake ventilation air. Disintegration, although not completely understood, is caused by shale dilation and weakening upon exposure to atmospheric moisture. Fluctuating moisture conditions are particularly deleterious, but may be at least partially controlled by tempering the air before it is brought to the working place. This paper discusses a 2-year program that was conducted on behalf of the Bureau of Mines to study the deterioration problem in mines.