(1) Evidence, including hearsay evidence, is admissible if in the judgment of the presiding officer it is the kind of evidence on which reasonably prudent persons are accustomed to rely in the conduct of their affairs. The presiding officer shall exclude evidence that is excludable on constitutional or statutory grounds or on the basis of evidentiary privilege recognized in the courts of this state. The presiding officer may exclude evidence that is irrelevant, immaterial, or unduly repetitious.

(2) If not inconsistent with subsection (1) of this section, the presiding officer shall refer to the Washington Rules of Evidence as guidelines for evidentiary rulings.

(3) All testimony of parties and witnesses shall be made under oath or affirmation.

(4) Documentary evidence may be received in the form of copies or excerpts, or by incorporation by reference.

(5) Official notice may be taken of (a) any judicially cognizable facts, (b) technical or scientific facts within the agency's specialized knowledge, and (c) codes or standards that have been adopted by an agency of the United States, of this state or of another state, or by a nationally recognized organization or association. Parties shall be notified either before or during hearing, or by reference in preliminary reports or otherwise, of the material so noticed and the sources thereof, including any staff memoranda and data, and they shall be afforded an opportunity to contest the facts and material so noticed. A party proposing that official notice be taken may be required to produce a copy of the material to be noticed.