30 CFR §57.22205
Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
In mines ventilated by multiple main fans, each main fan installation shall be equipped with noncombustible doors. Such doors shall automatically close to prevent air reversal through the fan. The doors shall be located so that they are not in direct line with explosive forces which could come out of the mine.