MSHA - Code of Federal Regulations - 30 CFR 57.22238
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MSHA - Title 30 CFR
30 CFR § 57.22238
Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

If methane reaches 2.0 percent in the mine atmosphere, all persons other than competent persons necessary to make ventilation changes shall be withdrawn from the mine until methane is reduced to less than 0.5 percent.