Code of Federal Regulations Title 30. Mineral Resources § 30.57.4461 Gasoline use restrictions underground

(a) The mine shall be nongassy and shall have multiple horizontal or inclined roadways from the surface large enough to accommodate vehicular traffic;

(b) All roadways and other openings shall connect with another opening every 100 feet by a passage large enough to accommodate any vehicle in the mine or alternate routes shall provide equivalent escape capabilities;  and

(c) No roadway or other opening shall be supported or lined with wood or other combustible materials.