30 CFR § 75.206
Conventional roof support.
(a) Except in anthracite mines using non-mechanized mining systems,
when conventional roof support materials are used as the only means of
support--
(1) The width of any opening shall not exceed 20 feet;
(2) The spacing of roadway roof support shall not exceed 5
feet;
(3)(i) Supports shall be installed to within 5 feet of the
uncut face;
(a)(3)(ii) When supports nearest the face must be removed to
facilitate the operation of face equipment, equivalent temporary support
shall be installed prior to removing the supports;
(4) Straight roadways shall not exceed 16 feet wide where
full overhead support is used and 14 feet wide where only posts are used;
(5) Curved roadways shall not exceed 16 feet wide; and
(6) The roof at the entrance of all openings along
travelways which are no longer needed for storing supplies or for travel of
equipment shall be supported by extending the line of support across the
opening.
(b) Conventional roof support materials shall meet the following
specifications:
(1) The minimum diameter of cross-sectional area of wooden
posts shall be as follows: