Section 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;(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: | Post length (in inches) | Diameter of round posts (in inches) | Cross-sectional area of split posts (in square inches) |
| 60 or less | 4 | 13 |
| Over 60 to 84 | 5 | 20 |
| Over 84 to 108 | 6 | 28 |
| Over 108 to 132 | 7 | 39 |
| Over 132 to 156 | 8 | 50 |
| Over 156 to 180 | 9 | 64 |
| Over 180 to 204 | 10 | 79 |
| Over 204 to 228 | 11 | 95 |
| Over 228 | 12 | 113 |
(2) Wooden materials used for support shall have the following dimensions:(i) Cap blocks and footings shall have flat sides and be at least 2 inches thick, 4 inches wide and 12 inches long.(ii) Crossbars shall have a minimum cross-sectional area of 24 square inches and be at least 3 inches thick.(iii) Planks shall be at least 6 inches wide and 1 inch thick.(3) Cribbing materials shall have at least two parallel flat sides.(c) A cluster of two or more posts that provide equivalent strength may be used to meet the requirements of paragraph (b)(1) of this section, except that no post shall have a diameter less than 4 inches or have a cross-sectional area less than 13 square inches.(d) Materials other than wood used for support shall have support strength at least equivalent to wooden material meeting the applicable provisions of this section.(e) Posts and jacks shall be tightly installed on solid footing.(f) When posts are installed under roof susceptible to sloughing a cap block, plank, crossbar or materials that are equally effective shall be placed between the post and the roof.(g) Blocks used for lagging between the roof and crossbars shall be spaced to distribute the load.(h) Jacks used for roof support shall be used with at least 36 square inches of roof bearing surface.53 FR 2375, Jan. 27, 1988, as amended at 55 FR 14228, Apr. 16, 1990; 55 FR 20137, May 15, 1990