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May 9, 2010

Emergency Preparedness In San Francisco

I've seen these brick circles in the pavement in San Francisco, but never paid them any attention. Coming from Boston, I'm used to seeing all kinds of historic relics embedded in the streets.
brick circle at 14th and Castro
14th and Castro.
Photo by Eli the Bearded.

Turns out, it's a piece of the history of the 1906 earthquake and conflagration.

Video from CBS 5 explaining what these are. They indicate a cistern that holds supplemental water for the fire system. In the center of each of these you find an access cover like this:
SFFD Cistern cover
Photo by Nick Sherman (a Bostonian!). (He's got at least 392 more manhole covers for you to look at!)

Google Map View of 14th & Castro with Fire Department Cistern
Google's satellite view gives a pretty clear image of the brick circle at 14th and Castro.

Google Streetview at 14th & Castro with Fire Department Cistern
Zooming down to Streetview we see this.
How ya like that Abbey Road effect?

partial brick circle on San Francisco Street
Not all the brick circles are being maintained so well.
Photo by seamstercolin.

The video said the hydrants connected to the cisterns are green-topped, so I went on a search for that.
green topped fire hydrant in San Francisco
Green-topped hydrant on Mission Street at Duboce Avenue
. Photo by jeneyepher. Note the number "8" stenciled on it. When we return to Google Streetview at 14th & Castro and look around for the hydrant, we find it on the southwest corner:
Green-topped Hydrant at 14th & Castro for Fire Department Cistern
See that it is also stenciled with an "8."

A search of Flickr for 'fire hydrant "san francisco"' turns up lots of hydrants, but only a few green-topped ones. There are a lot of blue-topped hydrants, though. (Blue ones, it turns out, are for the "High Pressure Auxiliary Water Supply System" - see below). Also red ones. If you find a gold one, it's the "hydrant that saved the Mission District" by somehow continuing to deliver water after the 1906 earthquake. If you find lavender or pink ones, they've probably been vandalized by Radical Faeries.

Going to the San Francisco Fire Department's own website turned up nothing, but a search at Google said the fire department used to have something. The page is cached, but renders itself invisible in Opera, Safari, Firefox and Chrome. If you look at the source, though, the text is all still there. Here I've copied it to save you all the bother.

Low Pressure Water Supply System

Water for fire fighting is supplied to the San Francisco Fire Department by the San Francisco Water Department system. This public water utility supplies the domestic and industrial water needs of the city as well as that required for fire service. Fire Service requirements include not only the water supplied to the Fire Department low pressure hydrants, but also the water supplied to the storage reservoir and tanks of the Fire Department High Pressure system. The supply of water to the City and the storage and distribution of water within the city is the responsibility of the Water Department. The location of all Fire Department hydrants as well as the maintenance and development of the entire Fire Department high pressure system is the responsibility of the Fire Department.

The Auxiliary Water Supply is used exclusively by the Fire Department for fire suppression.

High Pressure Auxiliary Water Supply System

The Auxiliary Water Supply System, more commonly known as the San Francisco Fire Department High Pressure System, is a system of mains and 1889 High Pressure Fire Hydrants, independent of the domestic water supply, built solely for the purpose of firefighting. The system is supplied with fresh water, by gravity, from a reservoir and two tanks located at high elevation in the city.

In the event the gravitational fresh water supply should fail, two pumping stations, located on the Bay Shore can, at a moment's notice, begin pumping salt water into the high pressure system. There are 5 manifolds along the bay to allow the fireboats to augment the system with bay water.

Anticipating the possibility of the high pressure pipelines being ruptured by earthquake, as happened to the mains of the Spring Valley Water Company in 1906, the entire distributing system was divided into three zones. The system incorporates the use of Gate Valves, placed at frequent intervals throughout the zones, by which a damaged section of the pipeline may be isolated and shut off separately, leaving the remainder of the system in operation.

The Auxiliary High Pressure Water Supply System is serviced and maintained by the San Francisco Bureau of Engineering and Water Supply.


The San Francisco Fire Department is provided with a system of underground cisterns having a total storage capacity of approximately 11 million gallons of water from which to draft. This cistern system consists of 172 cisterns strategically located throughout the city in the event of major damage to the distribution system of the Water Department and to the Fire Department High Pressure Supply System.

Fire Department cisterns have no connection to either the Water Department or high pressure supply system. They are under continual inspection by the Fire Department and are kept full by the Bureau of Engineering and Water Supply.

In addition to SFFD cisterns, practically all private and public water storage is available to the Fire Department for emergency use.

Here, the San Francisco Museum has a long and fascinating description of the whole system. The Alternative Water Supply System is "the only high-pressure network of its type in the United States." It was designed after City Engineer Marsden Manson studied water supply systems in 250 cities around the world in 1908. "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."

A 10.5 million gallon reservoir on Twin Peaks at 758 feet is the backbone. In the event that all fresh water is lost, there are two saltwater pumping stations that can deliver water at a pressure of 300 psi. There are also 36 other points where a fire truck can suck saltwater directly.
saltwater fire hydrant
I think this is one of those saltwater hydrants
. This one is on Pier 39. Photo by Micha84.

The hydrants in the lower zones are at a pressure of 160 psi. A fire commander can, if necessary, order the pressure to be increased to 214 psi and 328 psi by opening various reserve tanks in the system. If that isn't enough pressure, then the saltwater pumps can be added to the system.

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.

The pipes are joined with a "special double-beaded lead joint" that has been tested up to 450 psi. New pipe fittings are tested to 650 psi. The design is modified for pipes that are laid in areas built on landfill, since those areas are prone to liquefaction during an earthquake.

Valves are controlled remotely. "The two Central Control Processors (CCPs) are based on a VAX 4000 platform running a software package with a graphic user interface." The line of VAX 4000 computers was introduced in 1990 by Digital Equipment Corporation. The really neat thing about the San Francisco Fire Department's valve remote control system is that it can be controlled by either of the two fire boats that are always on patrol in the bay. So, in the event of total destruction, like the 1906 earthquake, the valves can still be operated from the safety of the bay - assuming the valves are still there, that the communication system is intact (antennas? wires?), and that there's some source of electricity.

Filed under California | permalink | May 9, 2010 at 11:32 AM



Posted by: logan at Feb 14, 2011 9:47:33 AM

Interesting info. I found your site while looking for more information on the locations of the cisterns. About 2 years ago when I was looking to buy a home in the Eureka Valley area, I toured a house that had a cistern in the basement -- not really a basement, but about 3 floors worth of structure built around one of the cisterns. It was really weird and spectacular, and I wish I had known more about the system back then. In any event, I can't remember where the house was, and I was trying to find more information about it. Thanks!

Posted by: ooeygooey at Sep 19, 2010 3:41:08 PM

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