Wash. Rev. Code § 50.12.120
No person shall be excused from attending and testifying or from producing books, papers, correspondence, memoranda, and other records before any duly authorized representative of the commissioner or any appeal tribunal in obedience to the subpoena of such representative of the commissioner or such appeal tribunal, on the ground that the testimony or evidence, documentary or otherwise, required of him or her may tend to incriminate him or her or subject him or her to a penalty or forfeiture; but no individual shall be prosecuted or subjected to any penalty or forfeiture for or on account of any transaction, matter, or thing concerning which he or she is compelled, after having claimed his or her privilege against self-incrimination, to testify or produce evidence, documentary or otherwise, except that such individual so testifying shall not be exempt from prosecution and punishment for perjury committed in so testifying.
RCW 50.12.120