Wash. Rev. Code § 35A.14.380
If a portion of a fire protection district including at least sixty percent of the assessed valuation of the real property of the district is annexed to or incorporated into a code city, ownership of all of the assets of the district shall be vested in the code city, upon payment in cash, properties or contracts for fire protection services to the district within one year, of a percentage of the value of said assets equal to the percentage of the value of the real property in the entire district remaining outside the incorporated or annexed area.
The fire protection district may elect, by a vote of a majority of the persons residing outside the annexed area who vote on the proposition, to require the annexing code city to assume responsibility for the provision of fire protection, and for the operation and maintenance of the district's property, facilities, and equipment throughout the district and to pay the code city a reasonable fee for such fire protection, operation, and maintenance.
RCW 35A.14.380