(1) All relevant evidence, including hearsay evidence, is admissible if, in the opinion of the board, the offered evidence is the kind of evidence on which reasonably prudent persons are accustomed to rely in the conduct of their affairs. The board may 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 board may exclude evidence that is irrelevant, immaterial, or unduly repetitious.

(2) The board's experience, technical knowledge, competency, and specialized knowledge may be used in evaluation of evidence.

(3) If not inconsistent with subsection (1) of this section, the board may refer to, but shall not be bound by, the Washington rules of evidence.

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