Washington is the only state with worker's compensation tax rates based on the hours worked, rather than per $100 in wages paid. Worker's compensation is not paid for hours the worker is off the job including paid sick leave, vacation or holiday hours and leaves of absence. Workers compensation rates vary by occupation and are comprised of three funds: the Accident Fund, Supplemental Pension Fund, and Medical Aid Fund. The Accident Fund is the only fund that the employer pays in full; up to half of the Supplemental Pension fund and Medical Aid fund can be expensed to the employee.

Source: http://www.lni.wa.gov/ClaimsIns/Files/Rates/2009RatesByBusTypeClassCode.pdf

For additional rate categories, click here.