Haw. Rev. Stat. § 269-10
In all investigations made by the public utilities commission, and in all proceedings before it, the commission and each commissioner shall have the same powers respecting administering oaths, compelling the attendance of witnesses and the production of documentary evidence, examining witnesses, and punishing for contempt, as are possessed by circuit courts. In case of disobedience by any person to any order of the commission or of any commissioner, or any subpoena issued by it or the commissioner, or of the refusal of any witness to testify to any matter regarding which the witness may be questioned lawfully, any circuit court, on application by the commission or a commissioner, shall compel obedience as in case of disobedience of the requirements of a subpoena issued from a circuit court or a refusal to testify therein. No person shall be excused from testifying or from producing any book, waybill, document, paper, or account in any investigation or inquiry by a hearing before the commission or any commissioner, when ordered to do so, upon the ground that the testimony or evidence, book, waybill, document, paper, or account required of the person may tend to incriminate the person or subject the person to penalty or forfeiture; but no person shall be prosecuted for any crime, punished for any crime, or subjected to any criminal penalty or criminal forfeiture for or on account of any act, transaction, matter, or thing concerning which the person shall under oath have testified or produced documentary evidence. Nothing herein shall be construed as in any manner giving to any public utility or any person immunity of any kind. The fees and traveling expenses of witnesses shall be the same as allowed witnesses in the circuit courts and shall be paid by the State out of any appropriation available for the expenses of the commission. All meetings and hearings of the commission shall be public.
HRS § 269-10