Washington Revised Code Title 34. Administrative Law § 34.05.458. Separation of functions

(1) A person who has served as investigator, prosecutor, or advocate in an adjudicative proceeding or in its preadjudicative stage, or one who is subject to the authority, direction, or discretion of such a person, may not serve as a presiding officer in the same proceeding.

(2) A person, including an agency head, who has participated in a determination of probable cause or other equivalent preliminary determination in an adjudicative proceeding may serve as presiding officer or assist or advise a presiding officer in the same proceeding unless a party demonstrates grounds for disqualification in accordance with RCW 34.05.425.

(3) A person may serve as presiding officer at successive stages of the same adjudicative proceeding unless a party demonstrates grounds for disqualification in accordance with RCW 34.05.425.