After the filing of a petition or petitions for review as provided for in RCW 51.52.104
, the proposed decision and order of the industrial appeals judge, petition or petitions for review and, in its discretion, the record or any part thereof, may be considered by the board and on agreement of at least two of the regular members thereof, the board may, within twenty days after the receipt of such petition or petitions, decline to review the proposed decision and order and thereupon deny the petition or petitions. In such event all parties shall forthwith be notified in writing of said denial: PROVIDED, That if a petition for review is not denied within said twenty days it shall be deemed to have been granted. If the petition for review is granted, the proposed decision and order, the petition or petitions for review and the record or any part thereof deemed necessary shall be considered by a panel of at least two of the members of the board, on which not more than one industry and one labor member serve. The chair may be a member of any panel. The decision and order of any such panel shall be the decision and order of the board. Every final decision and order rendered by the board shall be in writing and shall contain findings and conclusions as to each contested issue of fact and law, as well as the board's order based thereon. The board shall, in all cases, render a final decision and order within one hundred and eighty days from the date a petition for review is filed. A copy of the decision and order, including the findings and conclusions, shall be mailed to each party to the appeal and to his or her attorney of record.