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
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
- 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
- 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).
ISOs 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 =
|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.