Wash. Rev. Code § 35.103.050
Cities and towns conducting annexations of all or part of fire protection districts shall, at least through the budget cycle, or the following budget cycle if the annexation occurs in the last half of the current budget cycle, in which the annexation occurs, maintain existing fire protection and emergency services response times in the newly annexed areas consistent with response times recorded prior to the annexation as defined in the previous annual report for the fire protection district and as reported in RCW 52.33.040. If the city or town is unable to maintain these service levels in the newly annexed area, the transfer of firefighters from the annexed fire protection district as a direct result of the annexation must occur pursuant to RCW 35.13.238(4) through (8).
RCW 35.103.050