San Francisco Fire Department |
Water Supply System
by Steve Van Dyke, Superintendent
Bureau of Engineering and Water Supply
San Francisco Fire Department
Every San Franciscan is familiar with the great San Francisco Earthquake of April 18,
1906, and the conflagration which followed, leaving a major portion of the City in ashes.
Few people, however, know that most of the damage resulted not from the 'Quake, but
from the ensuing fires the worst fire in the history of the United States. More than
300 water main breaks and over 23,000 broken water services turned the water distribution
system into a sieve, and reduced water pressure to the downtown area. Four days later, by
the time the fire was finally extinguished on April 21, all of the City's downtown area was
destroyed. Twenty-five thousand buildings had burned 80 per cent of the
entire City's property value. It was the sixth time since 1849 that The City had burned to
The 1906 Earthquake crippled the City's water supplies, and left firefighters literally
drafting from sewers in an effort to halt the conflagration, and the people of San Francisco
blamed the destruction of the City on the failed water system. Insurance rates soared, and,
in some areas, coverage was unobtainable.
In 1908, Marsden Manson, the City Engineer, conducted a study of 250 cities throughout
the world to develop plans for a guaranteed water supply system for the sole purpose of
fire protection. Exhaustive tests of pipe materials, valves and hydrants were conducted, and
many eminent engineers of the period were consulted. All arguments were for a separate
fire combat water system and against a private system outside the jurisdiction of the Fire
The solution was the design and construction of the Auxiliary Water Supply System
(AWSS) for fire protection a separate and distinct water supply system for fire
protection use only with the Fire Department solely responsible for its
maintenance, operation and development. Adequate volume and pressure
were the primary foundations of the many ideas which eventually evolved into the San
Francisco AWSS. More water main pressure meant less dependency on the horse-
drawn steam fire engines of the era.
The AWSS remains the only high-pressure network of its type in the United States,
and was the only public project funded by the citizenry following the Great Earthquake of
1906. The system was developed with a $5.2 million bond issue approved by the people of
San Francisco in 1908.
Strongly influenced by the insurance companies of the period, the AWSS is dedicated to
the principle that the City will never again be destroyed by fire, at least not for lack of water
for fire fighting purposes. It is capable of covering a city block (100,000 square feet) with
water to a depth of 25 feet in one day.
Over the years, as the needs of the City have grown, the distribution system has been
improved and increased, from an original 72 miles of mains with 889 hydrants, to a 1997
total of 150 miles of 8- to 20-inch diameters mains, with 1,550 special
hydrants for a city of 47 square miles.
The AWSS system utilizes San Francisco's hilly terrain and waterfront perimeter to the best
advantage with an excellent combination of features. The structure and design of each
component illustrates how the design engineers aimed to defeat the devastating results of
earthquake and fire. These include:
Water Storage, Pressure and Elevation
Twin Peaks Reservoir the backbone of the system a 10.5-
million-gallon storage reservoir located on the City's Twin Peaks Mountains,
as originally envisioned by Chief Dennis T. Sullivan in the 1890's, at an elevation of 758
feet. This reservoir, constructed of reinforced-concrete slabs six inches thick, is
divided into two equal bays. Normal discharge flows from one bay only. In the event of a
sudden break in the pipeline distribution system, only one-half of the capacity would
be lost. The reservoir is normally supplied with fresh water by two 750 gallon-per-
minute centrifugal pumps drawing from the city's domestic water system. Saltwater
has better fire-extinguishing properties, but it is more destructive to fire fighting
Ashbury Tank of riveted steel construction on a reinforced-concrete
base at an elevation of 495 feet and with a capacity of 500,000 gallons, normally serves
elevations above the 150-foot contour. It has gated manifold connections to the
Twin Peaks Reservoir, but is only supplied with the higher pressure when required.
Jones Street Tank of reinforced concrete construction, at an elevation of 369
feet and a capacity of 750,000 gallons, supplies the mains below the 150-foot
elevation. This tank is staffed 24 hours per day, and has normally closed, gated manifold
connections to the Ashbury distributing system. When required, the reservoirs can be
interconnected to provide a total static pressure of 325 psi on the high-value
congested downtown districts.
When the entire fresh water system fails or is depleted, there are two emergency saltwater
pumping stations built on the Bay's shores, each with a pumping capacity of 10,000 gpm,
which can supplement the water supply with saltwater at a pressure of 300 psi. The
stations, built on solid rock, are self-contained, and can operate in the absence of
electric power utilizing their own self-contained generators. Originally powered by
huge three-story Babcock & Wilcox boilers driving Curtis steam turbines to turn the
Byron Jackson centrifugal pumps, technology has dictated a smaller, more modern diesel
power source, housed in steel-frame buildings with massive reinforced-
concrete walls, to keep the system in service.
When and if the emergency back up pump stations fail, two fireboats (originally the
Dennis T. Sullivan and the David Scannell), the Phoenix and the
Guardian can make hose connections directly into the AWSS via five special
manifolds along the Bay's perimeter. The Phoenix has a pumping capacity of over 9,600
gpm, equal to that of one of the stationary pumping facilities. The Guardian has the
largest pumping capacity of any fireboat in the world (24,000 gpm) and is the only fireboat
that is outfitted with a 5-1/2-inch monitor tip, capable of pumping 9,000 gpm onto a
fire from just one of its monitors.
A network of cast iron and special ductile iron
distributing pipes in three levels, or zones, with a total length of 150 miles of mains, fitted
with 1550 special hydrants, gate valves, and fireboat connections.
In a last-resort, worst-case, drop-dead scenario, a total of 175
independent, underground water cisterns are positioned beneath the intersections, most
with a capacity of 75,000 gallons, with some ranging up to 200,000 gallons.
Bay Suction Connections
Thirty-six water suction connections surround the City's waterfront to allow fire engines to
draft saltwater from the Bay of San Francisco.
Operation of the System
The mains in the lower zone at the city's base elevations are under a static pressure of 160
psi. If, during the process of a fire in the lower zone, the incident commander needs an
increase in pressure above that normally supplied to the lower zone, a radioed command
will put Ashbury Tank on the line; gate valves between the two zones will be opened by a
tank attendant at Jones Street Tank, and the pressure in the mains at the city's base will
increase to 214 pounds per square inch (psi). Should it be necessary to increase the
pressure further, another order will place the Twin Peaks Reservoir on the line and increase
the static pressure to 328 psi. If for any reason the quantity of water delivered in either zone
is not sufficient, the supply can be increased by placing either one or both of the saltwater
pumping stations in service.
The original pipe distribution system is constructed of special extra-heavy pit cast
iron pipe to meet the effects of earthquake shock, high operating pressures ranging up to
328 psi static, plus water-hammer and the possible use of saltwater. The pipe was
cast vertically to permit skimming of impurities. Integrally cast lugs with tie bars, as well as
concrete thrust blocks, provide end restraint, to minimize movement.
A special double-beaded lead joint was selected after conducting expulsion and
leakage tests at 450 psi on 19 leaded joints with different geometrical configurations. The
joint selected has proven its worth over the years, and the combined leakage, evaporation
and usage-per-mile of the system are normally considered low by water
During the 1906 earthquake, areas of filled or man-made ground experienced the
greatest amount of earth movement. It was therefore decided that a double-spigot
pipe with cast sleeves would be used in these areas. This arrangement provides great
flexibility, since the possible deflection at the joint is twice as great as that of standard bell
and spigot pipe. All intersecting mains, if serving the same zone, were connected with
special cast fittings to provide for maximum circulation of water. Gate valves were placed
so that any section of main could be shut off without blocking water from the hydrants
connected to adjacent sections of the main.
Specially designed dry barrel hydrants were used. The hydrants are equipped with three
3.5-inch male threaded outlets, each of which is independently valved. The main
valve at the base of the hydrant incorporates a special pilot valve, which balances water
pressure on both sides of the main valve and facilitates opening of the valve under high
pressure. The outlets are used to prevent direct connection of hose to the outlets and to
require the operator to use a pressure-reducing valve (a Gleeson valve) between the
hydrant and the 3-inch hose coupling. The Gleeson valve provides for control of the
flow and pressure into the hose, and absorbs any pressure surge which might occur when a
valve connected to a hose-line is suddenly opened or closed.
New Pipe Standards
The need for extensions and relocation of the distribution system has prompted the City to
update the original system with new materials and construction techniques. Because the
original cast materials were found to be extremely expensive to manufacture and install at
present-day labor costs, an investigation of available pipe, materials, fittings and
types of joints was conducted. In addition, tests on commercial and modified pipe were
performed at high pressures by pipe manufacturers and by the Fire Department.
Ductile iron pipe with push-on rubber-gasketed joints was selected as the
new standard. The material was chosen because of its high strength, ductility and resistance
to impact and corrosion. The push joint provides ease of installation, excellent capacity for
sealing at high pressures and flexibility at connections.
To provide a restraint against pipe joint movement resulting from the static pressure force,
special ductile iron collars were designed. These can be slipped onto the pipe and held
together with tie bolts. One collar is held by the pipe bell and is designated as the "bell
collar"; the other is held by steel stops welded to the spigot end of the pipe and is
designated as a "stop collar." The steel stops are only one inch in radial height, so they
effectively carry no bending load. The stop length varies from two inches for eight-
inch pipe to four inches for 20-inch pipe. The stops are welded to the pipe
using nickel iron rod.
Special ductile iron pipe fittings were designed to be used in conjunction with the modified
commercial pipe. To reduce pattern costs, the fittings utilize industry-standard laying
lengths which are typical for mechanical joint bells. The only modifications to the standard
consist of integrally-cast lugs for bolting to the pipe collars, and a slightly thicker
mechanical joint bell. All fittings are hydrostatically tested at 650 psi. The new pipe
specifications were designed by the Bureau of Engineering of the Department of Public
Works. The castings were manufactured by Olympic Foundry in Seattle, Washington.
High Tech Flow Controls
In an emergency situation, every second of time can mean lives. No one understands that
better the Fire Department. The AWSS, in conjunction with a new Supervisory Control
and Data Acquisition (SCADA) system, can now better ensure that the necessary
component for fire combat water is available immediately in any situation.
The AWSS allows for dynamic routing and rerouting of water throughout the three primary
zones of the system via valve sites. The challenge in emergency situations is to determine
where the water is needed to operate the valve. This can prove cumbersome and labor-
intensive; which is why SCADA was introduced.
Remote Control of Valves
The SCADA system operates on the existing 800 mHz trunked radio system in use city-
wide by the Department of Public Works. This existing infrastructure transports data
between central control points and Remote Terminal Units (RTUs). These are
minicomputers at each valve location, each capable of sending and transmitting information
over radio waves to a main control station. The system allows for monitoring and control
of a total of 80 main and bypass valves located throughout the City.
The two Central Control Processors (CCPs) are based on a VAX 4000 platform running a
software package with a graphic user interface. This is a very user-friendly
computer program that simplifies masses of technical jargon into pictures and icons on a
television monitor for ease of operation and speed. The two CCPs communicate with each
other and the RTUs by radio frequency and also by a back-up telephone wire line
connection, providing another level of insurance for system reliability. In addition to the
two main computer sites, the system offers four additional satellite control centers located
throughout the City to allow rapid decentralized response.
Another unique feature of the SCADA computer system is the provision of control
capabilities from either one of the two fireboats that patrol San Francisco Bay. This
challenge is met by providing radio link and laptop computers to the fireboats running the
same software program. These devices are also carried in the vehicles of the three Fire
Department division chiefs. This provides a full range of operational capabilities from many
decentralized points an invaluable asset in the event of a disaster.
Though in operation since 1912, the AWSS still has many integral sub-components,
all intended to meet the fire combat needs of a growing City. This fact remains true today
even with the recent enhancements. Ancillary work on the system is ongoing, and
expansion is anticipated into the next century.
Incorporated into the design of the AWSS is the ability to expand along with the ever-
changing needs of the City. The Pacific Board of Fire Underwriters reported to the
City Engineer, in 1908, that, once completed, the AWSS would be the best and most up-
to-date system of its kind in the world. The system may or may not still
warrant this distinction; however, it can be demonstrated that over the years it has served
the City well, providing a large concentration of water at the site of a fire in short order,
withstanding the many quakes that have shaken the City since 1906 and preventing major
For further information:
San Francisco Fire Department Business number (415) 558-3200
Fire Prevention - (415) 558-3300
Toy Program - (415) 558-3555
St. Francis Hook & Ladder Co. Museum - (415) 563-4630
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