Wash. Admin. Code § 381-60-150
All relevant evidence shall be admissible which, in the opinion of the presiding officer, is the best evidence reasonably obtainable, having due regard for its necessity, availability, and trustworthiness. "Relevant evidence" means evidence having a tendency to make the existence of any fact that is of consequence to the determination of the action more or less probable than it would be without the evidence. In passing upon admissibility of evidence, the presiding officer conducting the hearing shall give consideration to, but shall not be bound to follow, the rules of evidence governing civil proceedings in matters not involving trial by jury in the superior courts of the state of Washington. When objection is made to the admissibility of evidence, such evidence may be received subject to a later ruling. The presiding officer may, in his discretion, either with or without objection, exclude inadmissible evidence or order accumulative evidence discontinued. Parties objecting to the introduction of evidence shall state the precise grounds of such objection at the time evidence is offered.
Wash. Admin. Code § 381-60-150
91-14-029, § 381-60-150, filed 6/26/91, effective 7/27/91.