30 CFR § 57.4560
Mine entrances.
For at least 200 feet inside the mine portal or collar timber used for ground
support in intake openings and in exhaust openings that are designated as
escapeways shall be--
(a) Provided with a fire suppression system, other than fire
extinguishers and water hoses, capable of controlling a fire in its early
stages; or
(b) Covered with shotcrete, gunite, or other material with equivalent
fire protection characteristics; or
(c) Coated with fire-retardant paint or other material to reduce its
flame spread rating to 25 or less and maintained in that condition.
[50 FR 4082, Jan. 29, 1985, as amended at 50 FR 20100, May 14, 1985]
For further information: See MSHA's Program Policy Manual