Ohio Revised Code Title XLIX. Public Utilities § 4903.08

No person shall be excused from testifying or from producing accounts, books, and papers, in any hearing before the public utilities commission any public utilities commissioner, or any person appointed by the commission to investigate any matter under its jurisdiction, on the ground or for the reason that the testimony or evidence might tend to incriminate him, or subject him to a penalty or forfeiture. No such person shall be prosecuted or subjected to any penalty or forfeiture on account of, any transaction or matter concerning which he has testified or produced any documentary evidence. No person so testifying shall be exempted from prosecution or punishment for perjury in so testifying.