30 CFR § 75.1107
Fire suppression devices.
FIRE SUPPRESSION DEVICES AND FIRE-RESISTANT
HYDRAULIC FLUIDS ON UNDERGROUND EQUIPMENT
[STATUTORY PROVISIONS]
On and after March 30, 1971, fire-suppression devices meeting specifications
prescribed by the Secretary shall be installed on unattended underground
equipment and suitable fire-resistant hydraulic fluids approved by the
Secretary shall be used in the hydraulic systems of such equipment. Such
fluids shall be used in the hydraulic systems of other underground equipment
unless fire suppression devices meeting specifications prescribed by the
Secretary are installed on such equipment.