(a) Mine maps shall be revised and supplemented at intervals of not more than 6 months.

(b) Temporary notations shall include:   (1) The location of each working face of each working place;   (2) Pillars mined or other such second mining;   (3) Permanent ventilation controls constructed or removed, such as seals, overcasts, undercasts, regulators, and permanent stoppings, and the direction of air currents indicated;   (4) Escapeways and refuge alternatives designated by means of symbols.

[35 FR 17890, Nov. 20, 1970, as amended at 73 FR 80697, Dec. 31, 2008]