30 C.F.R. § 75.1107-11
Extinguishing agents; requirements on mining equipment employed in low coal
On mining equipment no more than 32 inches high, the quantity of extinguishing agent required under the provisions of §§ 75.1107-7, 75.1107-9, and 75.1107-10 may be reduced by one-fourth if space limitations on the equipment require such reduction.