Wash. Rev. Code § 51.12.090
The provisions of this title shall apply to employers and workers (other than railways and their workers) engaged in intrastate and also in interstate or foreign commerce, for whom a rule of liability or method of compensation now exists under or may hereafter be established by the congress of the United States, only to the extent that the payroll of such workers may and shall be clearly separable and distinguishable from the payroll of workers engaged in interstate or foreign commerce: PROVIDED, That as to workers whose payroll is not so clearly separable and distinguishable the employer shall in all cases be liable in damages for injuries to the same extent and under the same circumstances as is specified in the case of railroads in the first proviso of RCW 51.12.080: PROVIDED FURTHER, That nothing in this title shall be construed to exclude goods or materials and/or workers brought into this state for the purpose of engaging in work.
RCW 51.12.090
Effective dates-Implementation-1982 c 63: See note following RCW 51.32.095.