§ 33.121. General requirement.

   The owner, operator or superintendent of every mine shall provide and maintain a constant and adequate supply of pure air in the mine as provided in this subchapter. Pure air shall mean air containing not less than 19.5% oxygen, not more than 0.5% carbon dioxide and no harmful quantities of other noxious or poisonous gases. When it becomes necessary to install means for mechanical ventilation, prior to being placed in operation, the means for providing pure air shall be approved by the Department or its authorized representative.

   This section cited in 34 Pa. Code §  33.126 (relating to furnace ventilation).