Q: I live in San Francisco and I have old gas lines that are still very, very live. How can I locate the main line coming from the street? The blueprints for this building are long gone, since City Hall and most of the city burned down after the 1906 earthquake and fire. Is there any way of locating it?

A: The blueprints in the old City Hall wouldn’t help in locating gas lines, even if they had not gone up in smoke in 1906.

The regional utility company, PG&E, has the most up-to-date information about gas mains and services. As we’ve mentioned before, Kevin spent three summers repairing and replacing gas lines for a section of Oakland’s PG&E division in the 1970s.

Beginning in the 1970s, and extending to the present day, PG&E has been systematically replacing antiquated gas lines. The useful life of iron pipes was about 50 years — after that, they began to rust through and leak.

To compound the failure rate, the oldest pipes were joined with lead/oakum bell joints rather than welded together. Earth movement stressed these joints, creating leaks. There was many a day Kevin stood with his head down in a hole, re-leading these joints with a caulking tool and hammer and fitting them with a repair clamp made of rubber and iron.

We give this brief history lesson to point out that the gas main serving your home is probably not the 1906 version. It has probably been replaced at least twice during the last century. The main and service line are probably plastic, with the exception of a small section of iron pipe that comes out of the ground.

Locating the line coming into the house is simple. First, find your gas meter. On one side of the meter is a regulator. The regulator is a saucer-like device that looks a little like the Starship Enterprise (from "Star Trek") laid on its end.

Its purpose is to reduce the pressure of natural gas traveling from the main before it goes through the gas meter and enters the house lines. Pressure in the mains runs at 15 pounds per square inch and up — enough to create regular leaks in gas appliances.

The pipe going into the regulator is the main line coming from the street. Between the regulator and the point where the pipe exits the ground or enters the house you’ll notice a valve. This is the shutoff valve for the house. On the side of the valve is a horizontal bar. When the rectangular bar on the valve runs parallel to the pipe, the gas is on. When the rectangular bar is perpendicular to the pipe, the valve is off.

We recommend that you keep a 14-inch crescent wrench or a special gas-valve wrench near the meter, so that in case of an unexpected gas leak the valve can be turned off.

If it is necessary to turn the gas off, consider having a PG&E service worker come to the house and relight any pilot lights and verify that your gas appliances are operating properly.

***

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