Wash. Rev. Code § 51.12.060
The application of this title and related safety laws is hereby extended to all lands and premises owned or held by the United States of America, by deed or act of cession, by purchase or otherwise, which are within the exterior boundaries of the state of Washington, and to all projects, buildings, constructions, improvements, and property belonging to the United States of America, which are within the exterior boundaries of the state, in the same way and to the same extent as if said premises were under the exclusive jurisdiction of the state, and as fully as is permitted under the provisions of that act of the congress of the United States approved June 25, 1936, granting to the several states jurisdiction and authority to apply their state workers' compensation laws on all property and premises belonging to the United States of America, being 49 United States Statutes at large 1938, title 40, section 290 United States code, 1958 edition: PROVIDED, That this title shall not apply to employees of the United States of America.
RCW 51.12.060