Wash. Rev. Code § 49.60.150
No person shall be excused from attending and testifying or from producing records, correspondence, documents or other evidence in obedience to the subpoena of the commission or of any individual member, on the ground that the testimony or evidence required of the person may tend to incriminate or subject the person to a penalty or forfeiture, but no person shall be prosecuted or subjected to any penalty or forfeiture for or on account of any transaction, matter or thing concerning which the person is compelled, after having claimed the privilege against self-incrimination, to testify or produce evidence, except that such person so testifying shall not be exempt from prosecution and punishment for perjury committed in so testifying. The immunity herein provided shall extend only to natural persons so compelled to testify.
RCW 49.60.150