Fire-resistant hydraulic fluids and concentrates required to be employed in the hydraulic system of underground equipment in accordance with the provisions of Sec. 75.1107-1 shall be considered suitable only if they have been produced under an approval, or any modification thereof, issued pursuant to Part 35 Subchapter I of this chapter (Bureau of Mines Schedule 30), or any revision thereof. [37 FR 15301, July 29, 1972]