Ohio Rev. Code § 1567.59: Flame safety lamps.

The operator of an underground coal mine shall keep on hand in proper condition for use not less than one approved flame safety lamp, other approved methane detector, or other approved device capable of detecting methane gas in equivalent quantities as a flame safety lamp, for each fifty men employed in said mine, and upon the order of the deputy mine inspector, shall provide such additional flame safety lamps or approved methane detectors as are required to meet probable emergency.

This section does not apply to clay mines, except when such equipment is deemed necessary by the deputy mine inspector.

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