Wash. Rev. Code § 51.52.115
Upon appeals to the superior court only such issues of law or fact may be raised as were properly included in the notice of appeal to the board, or in the complete record of the proceedings before the board. The hearing in the superior court shall be de novo, but the court shall not receive evidence or testimony other than, or in addition to, that offered before the board or included in the record filed by the board in the superior court as provided in RCW 51.52.110: PROVIDED, That in cases of alleged irregularities in procedure before the board, not shown in said record, testimony thereon may be taken in the superior court. The proceedings in every such appeal shall be informal and summary, but full opportunity to be heard shall be had before judgment is pronounced. In all court proceedings under or pursuant to this title the findings and decision of the board shall be prima facie correct and the burden of proof shall be upon the party attacking the same. If the court shall determine that the board has acted within its power and has correctly construed the law and found the facts, the decision of the board shall be confirmed; otherwise, it shall be reversed or modified. In case of a modification or reversal the superior court shall refer the same to the department with an order directing it to proceed in accordance with the findings of the court: PROVIDED, That any award shall be in accordance with the schedule of compensation set forth in this title. In appeals to the superior court hereunder, either party shall be entitled to a trial by jury upon demand, and the jury's verdict shall have the same force and effect as in actions at law. Where the court submits a case to the jury, the court shall by instruction advise the jury of the exact findings of the board on each material issue before the court.
RCW 51.52.115