30 CFR § 27.31
A methane-monitoring system shall be tested by MSHA to determine its
functional performance, and its explosion-proof and other safety
characteristics. Since all possible designs, arrangements, or combinations
cannot be foreseen, MSHA reserves the right to make any tests or to place any
limitations on equipment, or components or subassemblies thereof, not
specifically covered herein, to determine and assure the safety of such
equipment with regard to explosion and fire hazards.