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.