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Calculating the Benefit Charge

Consistent with the statutory requirements, the benefit charge is based on the principle that the basic unit of public fire service is delivery of water to a fire. Accordingly, the Puget Sound Fire benefit charge formula focuses on correlating fire flow to the deployment of resources necessary for the “delivery of water to the fire.”

The Puget Sound Fire benefit charge formula can be summarized as follows:

  • The beginning point, which is driven by the size of the structure, establishes the minimum amount of water that is needed to put out a fire in a given structure(s).
  • Size is determined by finding the total square footage of all improvements on a property. Total square footage is determined by adding all gross square footage (outside measurements of building(s) and all floors, basements, garages and mezzanine spaces are added together to determine total square footage) on the property.
  • Puget Sound Fire then uses the formula to determine the resources (personnel and equipment) needed to deliver that base fire flow to a given (or group of) structure(s) on a land parcel.
  • The Puget Sound Fire formula breaks down structures by categories using four types; single and double family occupancies, manufactured homes in mobile home parks, multi-family or apartments, and commercial structures.


The benefit charge formula used is:

√square feet x (18)* x (category factor) x (response factor) x (risk factor)  x (fire flow factor) x (discount)

*18 is a coefficient value based on empirical tests by the Insurance Services Organization (ISO)

When the structural improvement(s) or uses within improvements on a commercial property have higher than normal risk as defined by the National Fire Protection Association in Standard 13, or other standards, the benefit charge formula adds to the base fire benefit charge as follows:

  • A 15% increase on automotive fuel dispensing stations/structures.
  • A 20% increase for big box retail, automotive fueling, repair and service facilities.
  • A 30% increase when products or uses with high combustibility or high rates of heat release are present.
  • A 40% increase when products or uses with high quantities of flammable, combustible or hazardous materials are present.


Factors in calculation of the benefit charge