Okla. Stat. tit. 45, § 45-507: Openings to be separated by natural strata

In all shaft mines the openings to the surface hereinbefore

provided for shall be separated from each other by natural strata at

all points by a distance of not less than one hundred fifty (150)

feet, and at all mines worked by slope openings, the distance

separating openings shall not be less than fifty (50) feet of

natural strata: Provided, that in any mine opened heretofore the

distance between said openings may be less, if the mine inspector of

the district shall deem it impracticable to comply with the

foregoing requirements. Where the two openings shall not have been

provided as hereinbefore required, the mine inspector shall cause

the second opening to be made in every mine without delay and in no

case shall furnace ventilation be used where there is only one

opening into the mine.