30 C.F.R. § 57.22221 Overcast and undercast construction (I-A, II-A, III, and V-A mines).
Title 30 - Mineral Resources
Overcasts and undercasts shall be— (a) Of substantial construction; (b)(1) Constructed of noncombustible materials; or (2) Where constructed of combustible materials, the outside surfaces shall be coated with at least one inch of construction plaster containing perlite and gypsum; at least one inch of expanded vermiculite, Portland cement and limestone; or other coatings with equivalent fire resistance; (c) Kept clear of obstructions.
Title 30: Mineral Resources
PART 57—SAFETY AND HEALTH STANDARDS—UNDERGROUND METAL AND NONMETAL MINES
Subpart T—Safety Standards for Methane in Metal and Nonmetal Mines
Ventilation
§ 57.22221 Overcast and undercast construction (I-A, II-A, III, and V-A mines).
