Why do San Francisco Fire Hydrants Look Weird?
Maybe it’s not the first thing you notice, but if you’re not from the city eventually you’ll probably pick up on the weird size and shape of Fire Hydrants within the city of San Francisco (and to a lesser extent surrounding suburbs).
Fire hydrants in North America have a remarkably standard appearance, enough that you can see the archetypal example embodied in a search for “Fire Hydrant Clip-art”.
- They have a single valve stem that runs through a domed lid
- They have two smaller fittings on either side (generally 2.5" connections) and (usually) a larger fitting in the front (generally a 4" connection)
- They’re several times taller than they are wide
Fire hydrants within San Francisco look like the weird fat cousin with boils compared to this standard image. Why is that?
over 80% of the city of San Francisco was destroyed
San Francisco has a fear of fire. After the 1906 earthquake, San Francisco largely burned to the ground, a lot of this is due to an inability to contain the fires for a variety of reasons (including new fires from trying to create firebreaks) and some from arson, in an amusing macabre way, because most properties were insured for fire damage but not for earthquake damage.
a fireman who told me that people in that neighborhood were firing their houses, as they were told that they would not get their insurance on buildings damaged by the earthquake unless they were damaged by fire — Captain Leonard D. Wildman of the U.S. Army Signal Corps
High Pressure Auxiliary Water Supply System
The city, in the course of replacing the rest of the city, built a new fire suppression supply system which was different in a few ways from the earlier system (and the way everyone else does it), it has multiple zones with an extensive system of valves to ensure there’s not just the ability to shut off individual supply lines but entirely separate supply systems to different areas of the city and even redundancies in the water storage. Water storage itself is different, most systems are supplied with water pressurized and fed along with the usual municipal potable water system but that requires pumps operate to actively pressurize the system and a continuous supply of fresh water; the AWSS is supplied by a series of reservoirs holding standing water and, more pertinently, water standing at the top of hills which results in high-pressure water from gravity alone (160psi to over 300psi while typical municipal supplies are around 40 to 100psi). In the event of failure, the system can also be supplied by salt-water pumped out of the bay by dedicated pumping stations or fireboats.
The high-pressure is designed to allow directly feeding several attack hoses from a hydrant without the need for a pumper truck and, this characteristic, changes the design of the hydrant. Notably the passages are larger to avoid friction losses and they have per-outlet valves in addition to the main gate valve.
Beyond the High Pressure Fire System, the county also has a (mostly) conventional low pressure system as well as system of cisterns located throughout the city (mostly under intersections).
Further reading (aka don’t make me figure out where to cite this):
About San Francisco in particular
- City and County of SF on fire systems
- Wikipedia on the Auxiliary Water Supply System
- Quora answer on the color of SF Fire Hydrants
- SF Gate on the incompatible size of the Low Pressure Fire System’s coupling
On Fire Hydrants as a whole
- Wikipedia on Fire Hydrants
- A Brief History of the Hydrant
- All about Hydrants (from the Fire Museum of Canada)
- Fire Nuggets on pressurizing a dry standpipe (via Archive.org)
- A guide (accurate to California) on Hydrant Colors
