Wash. Rev. Code § 49.66.100
The arbitration board, acting through its chair, shall call a hearing to be held within ten days after the date of the appointment of the chair. The board shall conduct public or private hearings. Reasonable notice of such hearings shall be given to the parties who shall appear and be heard either in person or by counsel or other representative. Hearings shall be informal and the rules of evidence prevailing in judicial proceedings shall not be binding. A recording of the proceedings shall be taken. Any oral or documentary evidence and other data deemed relevant by the board may be received in evidence. The board shall have the power to administer oaths, require the attendance of witnesses, and the production of such books, papers, contracts, agreements, and documents as may be deemed by the board material to a just determination of the issues in dispute and to issue subpoenas. If any person refuses to obey such subpoena or refuses to be sworn to testify, or any witness, party, or attorney is guilty of any contempt while in attendance at any hearing held hereunder, the board may invoke the jurisdiction of any superior court and such court shall have jurisdiction to issue an appropriate order. A failure to obey such order may be punished by the court as a contempt thereof. The hearing conducted by the arbitrators shall be concluded within twenty days of the time of commencement and, within ten days after conclusion of the hearings, the arbitrator shall make written findings and a written opinion upon the issues presented, a copy of which shall be mailed or otherwise delivered to the employees' negotiating agent or its attorney or other designated representative and to the employer or the employer's attorney or designated representative. The determination of the dispute made by the board shall be final and binding upon both parties.
RCW 49.66.100