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Alternative Water Supplies

The Fire Suppression Rating Schedule (FSRS) recognizes alternative water-supply systems, including dry hydrants, suction points, large-diameter hose relays, and hauled water using tanker shuttles.

The water-delivery system must be available 365 days a year and provide 250 U.S. gpm for a two-hour duration within five minutes of the arrival of the first apparatus. If a community uses a dry hydrant or suction supply point, ISO may need certification of the water capacity available during a 50-year drought cycle. Many state and local governments have geological engineers or hydrologists who can provide that information. A good place to start is with the local department of environmental conservation.

ISO treats suction points — with or without dry hydrants — in the same way it treats standard fire hydrants. Any property within 1,000 feet of a creditable suction point may be eligible for a protection class better than Class 9, provided the building is within five road miles of a responding fire station and the community has obtained 20% credit or more under the FSRS.

ISO may extend credit beyond 1,000 feet of a fire hydrant when the company uses large-diameter hose, if the fire department can demonstrate a standard procedure for deployment of hose and also establish a relay operation.

ISO may extend credit for the use of tanker-shuttle operations. In general, ISO divides the tanker capacity (minus 10% to account for spillage and incomplete filling and discharge) by the sum of the fill time, round-trip travel time, and discharge time of each tanker to determine a gpm capability. ISO considers all tankers, as well as the use of automatic-aid apparatus. If the community is capable of increasing the 250 gpm within 15 minutes of the arrival of the initial apparatus, and maintaining the flow for the duration (usually two hours), ISO will credit the higher delivery rate.

To determine your fire department's eligibility for recognition of a tanker shuttle, ISO needs to understand the delivery capability of each apparatus. ISO considers:

  • fire-site pump capacity
  • drop-tank capacities
  • distance of responding apparatus from the fire station to the fire site
  • distance of responding supply pumper to supply site
  • distance from the fire site to the supply site
  • amount of water carried by apparatus
  • discharge rate of water-supply apparatus
  • fill rate of water-supply apparatus
  • quantity of water available and the rate available from the supply source
  • set-up times

The procedure for determining your system's capability involves running a time-line analysis. ISO considers apparatus arrival times, travel times, discharge rates, fill rates, fire flow at the fire site, wait time for apparatus to fill or discharge their water supply, and supply delivery capability.

In grading a community, ISO does consider apparatus — including tankers, supply-point pumpers, and relay pumpers — that support the alternative water-supply effort as in-service engine companies. ISO does not consider apparatus located more than 1,000 feet from the fire site as fire-site engine companies. However, ISO does consider firefighters remaining at the fire site as company personnel.

ISO considers that second-alarm apparatus operated by paid drivers leave their fire stations 3 minutes after arrival of the first apparatus at the fire site. ISO considers that second-alarm apparatus operated by volunteer drivers leave their fire stations 6 minutes after arrival of the first apparatus at the fire site. The delay covers the time needed for decision (2 minutes), communication (1 minute), and assembly (3 minutes).

ISO’s calculations assume that fire apparatus travel at 35 mph on average. ISO calculates the travel time according to the formula:

T = 0.65 + 1.7D
where T =
D =
the travel time in minutes
the distance in miles

ISO uses slower speeds for underpowered apparatus or apparatus laying hose lines.

For more information . . .
. . . on any topic related to the PPCTM program or the Fire Suppression Rating Schedule, click Talk to ISO Mitigation, or call the ISO mitigation specialists at 1-800-444-4554.

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Mainstream Dry Hydrants Inc. is a leading promoter, supplier and installer of top quality, dry hydrant systems for rural Fire Departments.