30 CFR 57.4461 - Gasoline use restrictions underground.
If gasoline is used underground to power internal combustion engines -
(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.