SFFD high-voltage system built after the 1906 earthquake

The high-pressure system in San Francisco is one of the excellent water distribution systems dedicated to fire fighting in the United States.

In the late 19th century, especially during the administration of Chief Dennis T. Sullivan, proposals for the establishment of such a system were made. But it wasn't until the 1906 San Francisco earthquake and Chief Sullivan's death in that disaster that funds were in place. The chief brought the land purchase of the Shuangfeng Reservoir, and the fire prompted the city to allocate funds in 1907 to research and plan an independent water supply system for the fire department.

The decision to build the SFFD high-pressure system also included the provision of auxiliary brine from the San Francisco Bay and the maintenance and expansion of the water tank system. So in 1908, a US$5.2 million bond issuance was voted through, and the high-voltage system was officially accepted by the San Francisco Fire Department in January 1914.

The initial installation included the Twin Peaks Reservoir, a 10.5 million gallon reinforced concrete reservoir on Twin Peaks, with a water level of 758 feet; Ashbury Tank, a 500,000 gallon steel storage tank on Clayton Street opposite Carmel Street, with a water level of 494 feet; And Jones Street Tank, a reinforced concrete storage tank located on Jones Street, between Clay Street and Sacramento Street, has a storage capacity of 750,000 gallons and a water level of 369 feet. Approximately 72 miles of super-heavy cast iron distribution manifolds radiated from these supply sources to the entire city's business districts, and supplied 889 high-pressure fire hydrants.

In order to provide the use of the bay's salt water as an emergency supply, two pumping stations were built on the shore of the bay. Pumping station No. 1 is located at the northwest corner of Second Street and Townsend Street. Pumping station 2 is located on Van Ness Avenue, next to Fort Mason. These stations contain pumping equipment that can pump brine into the high-pressure system at any time. If necessary, the water can be pumped from the bay to the Shuangfeng Reservoir, or, by operating street valves, the water can be directed to a high-pressure main in any desired direction. The maximum combined capacity of the two pumping stations is 24,000 gmp and the pressure is 300 psi.

Following Chief Sullivan’s recommendations, 54 cisterns were restored and 85 reinforced concrete cisterns were constructed, each with a capacity of 75,000 gallons. The capacity of old brick cisterns ranged from approximately 10,000 to 95,000 gallons. More cisterns were built later, so the department now has 151 cisterns.

The reservoir and the two main source water tanks are backed up by two brine pumping stations and fire boat manifolds

The sister ships Dennis Sullivan and David Scanner, the two firefighting ships, were also obtained through the issuance of high-voltage system bonds. Although primarily designed to protect the waterfront, these ships are able to deliver salt water to the high-pressure system main via a special manifold connection.

Every practical protective measure to prevent earthquake damage is included in the high-voltage system. The distribution system is divided into upper and lower areas. The upper area is usually supplied by Ashbury Tank and includes pipelines of 150 feet or higher. All pipes in the upper zone are on solid ground. The lower area is usually supplied by Jones Street Tank and includes all pipes below 150 feet above sea level. A large part of the pipeline in the lower area is laid on the filled or made ground and is designated as a "weak area".

Foresee the possibility that high-pressure water pipes may rupture due to earthquakes, just like water pipes in 1906, the weak area is divided into multiple independent units, so that closing a gate valve can close the weak area without affecting the rest of the system. Gate valves are frequently installed in the two areas so that damaged pipes or fire hydrants can be shut off individually and the rest of the system can continue to operate.

The pipes are super heavy cast iron, ranging in diameter from 10 to 20 inches, with 8-inch branches to the fire hydrant. A special type of pipe joint increases flexibility in filling areas affected by ground subsidence. The pumping station is built on solid rock. Each site is connected to the distribution system through two independent feeders.

Since its initial installation, the high-voltage system has been expanded, and it has now become the main source of fire protection in almost all important industrial and commercial high-value areas, as well as many tightly constructed residential areas. It allows rapid concentration of powerful streams without the use of a pump. It is considered by the American Insurance Association's rating engineers as the most valuable fire protection feature.

The system is controlled by a committee of fire commissioners and department heads. The mechanical engineer in charge of the fire department engineering and the water supply bureau is responsible for the maintenance, repair and normal operation of the system. Each pumping station and storage tank has qualified personnel on duty continuously, and there is a duty officer on duty in the gate building of Shuangfeng Reservoir during the day.

The system usually supplies fresh water by gravity from Ashbury and Jones Street Tanks located at medium altitudes. The fresh water supply from the Shuangfeng Reservoir at high altitude can be used to increase the pressure of the entire system and replenish the storage tanks if necessary. The two pumping stations are ready to supply emergency brine at any time. Six manifolds are provided through which the fire boat can pump salt water into the system.

Two water storage tanks usually supply fresh water through the connection with the water distribution pipe of the water department. Twin Peaks Reservoir is usually filled with two 750-gpm electric centrifugal pumps from the Ashbury tank, and the pumps are discharged from the reservoir to the tank through a feeder. Emergency water supply is also provided to the reservoir through a 6-inch gated pipeline, which is connected to the water supply department pipeline to supply the Summit Reservoir. The brine supply for each pumping station is obtained from the bay through a concrete tunnel with a diameter of 5 feet.

The high-pressure main is used only for the supply of fire hydrants and currently protects approximately 15 square miles. The area includes approximately 1,400 high-pressure fire hydrants and 115 miles of pipelines. According to the municipal regulations, except for the fire department, any municipal department and private enterprise are not allowed to use the high-voltage system. The system does not allow connection of sprinkler systems.

— Chet Born's San Francisco FD photo.

High-pressure fire hydrants are distributed in crowded high-value areas so that 15,000 gpm can be concentrated in an area of ​​approximately 100,000 square feet, with hoses not exceeding 400 feet. In other parts, 8,000 to 10,000 gpm can be concentrated on a single block. There is at least one high-pressure fire hydrant at every intersection in the system coverage area. There is a middle fire hydrant in the long block and additional fire hydrants in the crowded area. Under no circumstances should the distance between high-pressure fire hydrants exceed 900 feet.

The high-pressure fire hydrant is made of overweight cast iron and provides three 3 1/2-inch independently gated outlets. The practice of the fire department requires the connection of the Gleeson pressure relief valve when using a high-pressure fire hydrant. Each valve has two 3-inch outlets. When a Gleeson valve is connected to each hydrant outlet, six 3-inch outlets can be used for hose lines. The Gleason valve has an adjustable regulator to control the hose pressure.

In the lower area of ​​the high-pressure system, the average static pressure of the fire hydrant is 130 psi and the upper area is 143 psi. At the city base, the static pressure provided by Jones Street

The fuel tank is 160 psi; from Ashbury Tank, 214 psi; from Shuangfeng Reservoir, 328 psi. The normal supply in the lower area comes from Jones Street Tank, while Ashbury Tank and Twin Peaks Reservoir provide pressure and supply increases. The normal supply in the upper area comes from Ashbury Tank, and the Shuangfeng Reservoir provides pressure and volume increase. The distributor pipe extends from one of the feeders between Twin Peaks Reservoir and Ashbury Tank. This pipeline supplies the fire hydrant between Ashbury Tank and Twin Peaks Reservoir. These special fire hydrants cannot increase the pressure and capacity supply. These fire hydrants are marked by black bonnets and fire hydrant outlet caps.

By indicating the pressure gauges maintained on each storage tank, the available pressure of the entire high-pressure system is continuously monitored. The No. 2 pump station and the fire alarm headquarters are equipped with two regional pressure recorders. The lower area also has a pressure recorder at No. 2 Engine Company and No. 1 Pump Station. Any pressure fluctuations will be reported to the Engineering and Water Supply Bureau immediately, and an investigation will be carried out immediately.

The San Francisco Fire Department also has an underground reservoir system with a total storage capacity of 10,176,214 gallons of water. 151 reservoirs are strategically distributed throughout the city, which can provide reliable emergency water supply to the fire department when major damage occurs in the distribution system of the water supply department and the high pressure system of the fire department. According to the grouping of reservoirs, the system can be divided into two categories. One category includes reservoirs that are individually located at the point where the underground water pipe is estimated to be most susceptible to impact damage. Another category includes reservoirs surrounding or located around a point where it is estimated that a large fire can be controlled.

The green cap on the low-pressure fire hydrant indicates that the nearby water tank is available. The fire department’s reservoir has no connection with the water supply department or the high-pressure system. They are continuously inspected by the fire department and kept full by hoses connected to the fire hydrant when necessary. The oldest cistern in use (built in 1854) has a capacity of 19,200 gallons and is located on Powell Street and Ellis Street. The newest reservoir was built in 1959. The 112 fire department reservoirs have a capacity of 75,000 gallons. A reservoir was built in 1959 and is located in the Civic Center with a capacity of 243,000 gallons. Almost all reservoirs are located at street intersections, and pumps can pump water from the reservoirs through manholes. Usually, each manhole can have two pumped water.