49 C.F.R. § 173.311
The following packing instruction is applicable to transportable UN Metal hydride storage systems (UN3468) with pressure receptacles not exceeding 150 liters (40 gallons) in water capacity, and having a maximum developed pressure not exceeding 25 MPa. UN Metal hydride storage systems must be designed, constructed, initially inspected, and tested in accordance with ISO 16111:2018 (IBR, see § 171.7 of this subchapter), consistent with § 178.71(m) of this subchapter. Until December 31, 2026, UN Metal hydride storage systems may instead conform to ISO 16111:2008(E) (IBR, see § 171.7 of this subchapter). Steel pressure receptacles or composite pressure receptacles with steel liners must be marked in accordance with § 173.301b(f) , which specifies that a steel UN pressure receptacle displaying an "H" mark must be used for hydrogen-bearing gases or other gases that may cause hydrogen embrittlement. Requalification intervals must be no more than every five years, as specified in § 180.207 of this subchapter, in accordance with the requalification procedures prescribed in ISO 16111:2018 or ISO 16111:2008.
49 C.F.R. §173.311