Ohio Revised Code Title XV. Conservation of Natural Resources § 1563.16

In the development of mines, doors shall be eliminated wherever practicable. All main or principal air currents shall be controlled by double doors to form an air lock, said doors to be self-closing and to be a sufficient distance apart to accommodate any trip that may be handled through them, thus having one door closed at all times. At all points where double doors are impracticable and single doors are used, there must be an attendant in charge of said door unless a self-closing door approved by the deputy mine inspector is used. A hole for shelter shall be provided at each door to protect the attendant from danger from cars while performing his duties. Persons when regularly employed for this purpose shall remain at the doors at all times during working hours. The same attendant may attend two doors if his absence from the first door does not endanger the safety of the employees. At every door on any incline plane or road whereon haulage is done by equipment other than locomotives, an attendant shall always be on duty during working hours, and an extra door shall be provided for use in case of necessity. Except where double doors are used, a spare or standby door shall be installed adjacent to all regular doors on main haulage roads for emergency use. The responsibility for closing doors shall rest upon the person who opens them. This section does not apply to clay mines.

No operator of a mine shall refuse or neglect to comply with this section.