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