Okla. Stat. tit. 45 § 509
When any mine is operated by a shaft which exceeds seventy-five (75) feet in vertical depth, the persons employed in said mine shall be lowered into and raised from said mine by means of machinery, and where the employees are lowered into and hoisted from the mines at the main shaft opening, the other shaft shall be supplied with safe and suitable machinery for hoisting and lowering persons, or with safe and convenient stairs for use in cases of emergency by persons employed in said mine: Provided, that any mine operated by two shafts, and where safe and suitable machinery is provided at both shafts for hoisting coal or other mineral, or persons, as herein provided for, shall have sufficiently complied with the requirements of this section.
Okla. Stat. tit. 45, § 509