Wash. Rev. Code § 38.52.200
Liability for the compensation provided by this chapter, as limited by the provisions thereof, is in lieu of any other liability whatsoever to an emergency worker or his or her dependents or any other person on the part of the state, the agency, the local organization for emergency management with which the emergency worker is registered, and the county or city which has empowered the local organization for emergency management to register him or her and direct his or her activities, for injury or death arising out of and in the course of his or her activities while on duty as an emergency worker: PROVIDED, That nothing in this chapter shall limit or bar the liability of the state or its political subdivisions engaged in proprietary functions as distinguished from governmental functions that may exist by reason of injury or death sustained by an emergency worker.
RCW 38.52.200