Okla. Stat. tit. 45, § 45-509: Hoisting machinery in shaft over seventy-five feet deep

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.