PHMSA has safety authority over the underground storage facilities used in natural gas pipeline transportation, but has no safety regulations in the DOT Code (49 CFR Part 192) that apply to the down-hole underground storage reservoir for natural gas. PHMSA issued an interim final rule that requires operators of underground storage facilities for natural gas to comply with minimum safety standards, including compliance with API RP 1171, Functional Integrity of Natural Gas Storage in Depleted Hydrocarbon Reservoirs and Aquifer Reservoirs, and API RP 1170, Design and Operation of Solution-mined Salt Caverns Used for Natural Gas Storage. The interim final rule adopted the non-mandatory provisions of the RPs in a manner that would make them mandatory, except that operators are permitted to deviate from the RPs if they provide justification. The next planned action is to finalize the interim final rule.