ISO Mitigation SLIDERS v03 Fire

Forty points of a community’s Public Protection Classification (PPC™) grading is based on its water supply. ISO looks at whether there is sufficient water for fire suppression beyond the community’s maximum daily consumption for other purposes.

Minimum criteria

For your community to be eligible for a PPC of Class 8 or better, your water supply system must be able to deliver at least 250 gpm for a period of 2 hours. That flow is in addition to the community’s maximum daily rate of consumption for purposes other than firefighting.

If the fire department delivers the 250 gpm through tanker shuttle, large-diameter hose, or other alternative water supply, the water must be available within 5 minutes of the arrival of the first-due apparatus, and the department must maintain the flow, without interruption, for the 2-hour duration.

Class 8B

If a community has superior fire protection services and fire alarm facilities but lacks the water supply required for a PPC of Class 8 or better, the community may be eligible for a Class 8B rating. For more information, see “Minimum Criteria for Class 8B.” Evaluation of systems that exceed the minimum requirement.

If your water supply meets the 250 gpm minimum, ISO will evaluate your system — together with factors relating to your fire department and your fire alarm and communications systems — to determine whether you qualify for a PPC of Class 8 or better.

Within the Fire Suppression Rating Schedule (FSRS), a section called “Needed Fire Flow (NFF)” outlines the methodology for determining the amount of water necessary for providing fire protection at representative locations throughout the community. To evaluate your community’s water supply, ISO calculates the NFF for selected locations. We then determine the water flow capabilities at those locations and calculate a ratio considering the need (NFF) and availability (water flow capability). We use that ratio in calculating the credit points identified in the FSRS.

ISO calculates the NFF for an individual building based on the building’s area, construction, occupancy, and exposure. To get full credit, the water supply must be able to deliver water at 20 psi residual pressure and at the specified rate of flow for a specified period of time. NFFs for individual buildings range from a minimum of 500 gpm to a maximum of 12,000 gpm. For more information, see the Guide for Determination of Needed Fire Flow.

Buildings not considered in the community’s PPC

For purposes of calculating your community’s PPC, ISO does not normally consider the NFF at certain high-demand properties. Those properties include buildings with an NFF in excess of 3,500 gpm.

ISO individually grades the protection of buildings with an NFF in excess of 3,500 gpm, and their PPC can differ from that of the community or district that provides their fire protection.

Evaluation method

ISO analyzes three primary factors in the evaluation of the water supply at each representative site in your community:

  • capacity of the supply works
  • capacity of the water mains or distribution system
  • distribution of hydrants

We analyze each of those factors according to applicable standards of the National Fire Protection Association (NFPA) and the American Water Works Association (AWWA). In addition, ISO evaluates the type and installation of hydrants and/or suction points throughout your community or district, along with any program of hydrant inspections and flow testing. You receive additional credit points based on that evaluation.