Home & Garden Columns

About the House: The Truth About Seismic Gas Shut-Off Valves

By Matt Cantor
Friday October 13, 2006

The anniversary of the Loma Prieta is upon us once again and still so little has been done to prepare for our earthquake. That’s right. Loma Prieta wasn’t ours. It was in the mountains of Watsonville nearly 100 miles to the south. 

The way the news media works tends to blow things out of proportion and if you watched the news following that quake, it made it seems as the though it were 1906 all over again. It wasn’t. That quake was devastating for the very few houses that were nearby and it actually threw a few houses in the mountains near the epicenter several feet (or yards) from their foundations. Also, the downtown of Santa Cruz nearly collapsed and it was some miles away.  

We were so much further away that even brittle structures like chimneys were barely affected in most of the Berkeley/Oakland area. 

When we think about failures like the Bay Bridge and the Cypress structure, it’s easy to imagine that Loma Prieta was like a Big One but for us it wasn’t even close. These structures, as well as houses located in the Jiggly-land of the Marina district in S.F. are true exceptions and should not be how we gauge failure. When the Hayward finally slips, it might be several thousand times the shaking force of Loma Prieta for us.  

Berkeley seems to get it’s share of Richter scale 4’s and something closer to a 5 once in a great while. Most of us have never experienced anything more than about a 4 in Berkeley and that would be about 1/30,000 of the size of a Richter 7 in the same place. Most people assume that the Richter scale of seismic magnitude is a decimal scale with each number being 10 times greater than the last. It is, in fact, a logarithmic scale with each number being about 30 times that of the last, so a 6 is about 1,000 times that of a 4 and a 7 is about 30,000 time the same. 

So it’s a fair statement to say that the East Bay hasn’t really been hit by an earthquake of any significance since long before the oldest houses now standing were built. 

Now, this doesn’t mean that you can’t retrofit a house and withstand the shaking force of an earthquake. There’s a lot of science going on today that says that we can, in fact, built to withstand really big earthquakes and we can also retrofit houses to withstand a large force. So like Nike says, “Just Do It.” It ain’t all that much money and it’s better than giving it to the insurance companies (although you’re welcome to do that TOO if you insist … and if you believe they’ll be able to pay up after it’s all gone down, so to speak). 

Now, I’m not going to go into a whole retrofitting thing today and in my usual circuitous fashion, I’m finally getting around to the point I’ll like to make, that being, that in an earthquake, it’s fire that you need fear most of all. 

It’s actually quite unlikely that you’re going to die by being crushed under the weight of a falling building during an earthquake. These wooden packing crates we house ourselves in, seem generally to stay fairly intact during even very large earthquakes, although they may have crushed the basement or crawlspace in the process (so the basement might not be the best place to be). BUT, when gas lines break, they can fill up the interiors of houses, basement or garages and result in explosions and fires.  

If you followed the damage done during the Northridge earthquake near L.A. in 1994, you know that most of the damage was done by fires caused by gas explosions. Water heaters were found everywhere except where they’d been installed and some were found 30 feet away. Although data is harder to gather on the 1906, it looks as though a significant portion of damage was also caused by the same thing. 

This is why two special laws have been enacted in California in the past decade. One regarding the strapping of water heater and one regarding automatic seismic gas shut-off valves. The first is state-wide and pertains to the sale of all houses. A homeowner is required to properly (there’s a magical word if ever there was one) strap the water heater prior to delivery to the new owner. This is almost never done right and you can get a document from the state that has nice clear drawing that will clearly show just how wrong your strapping might be. 

The second law applies to the city of Los Angeles and is the first in the nation to require the insulation of an automatic seismic gas shut-off valve on any house being sold. Hooray for L.A. 

Allstate insurance is apparently beginning to make the installation of some type of gas safety valve a requirement for their customers and I think that’s a good thing. I also think that L.A. and Allstate are not going to be isolated in these requirements for long. Alameda county has a toothless law that I’ve never seen enforced in any way as does Marin and Contra Costa.  

Although these laws (mostly dating from the early 2000’s) haven’t seen much daylight yet, I’m happy to say that I think it’s just a matter of time. It wouldn’t surprise me in the least if Berkeley, Oakland or El Cerrito started making these devices requisite on new construction any time now. 

These devices fall into two categories. There is a seismically activated type which responds to shaking force and a flow type which senses excessive flow. 

The first type usually contains a ball which rests in a socket of some sort. When shaking hits 5.4 on the Richter scale, the ball falls out and a mechanism of some sort triggers the valve to close. It’s actually very simple.  

Most of the valves sold today have some sort of reset device built right onto the valve so that you can take a little screwdriver and turn your gas back on. Be sure to get help and check the whole house thoroughly, including the crawlspace at the time to reactivate the gas. Utility reps will be in short supply so you’d best be able to do this yourself after we’ve had a quake. 

The second type is designed to sense breakages in the piping. When we run the stove and the water heater and the dryer, we still only allow for a limited rate of flow through the main pipe. When a pipe breaks completely, the flow will be greater than that and this is what these valves sense. When this occurs they plug shut. It’s another simple mechanism that involves a spring loaded plug that requires enough wind to drag to the shut position. I don’t favor these for us due to the fact that you can get many small breaks in your gas piping and not set them off. When an earthquake occurs, a seismically activated valves will go off regardless of the size or number of leaks created. 

There are a number of valves that are approved and most are quite cheap (mostly under $100). The Little Firefighter is a favorite of mine, although I also like the Northridge and the Vanguard. You can search them online and you can also check out our own Berkeley supplier, gasvalvedoctor.com. Boaz Levanda (843-3275) is a nice chap who’ll be happy to sell you one. He’s also been a one man legal squad trying to get the permit requirements reduced so that they can be installed for fewer bucks.  

A plumber is the right person to install such a device and the cost seems to be around $200-$300 for installation (plus the valve). It’s usually quite simple but can be more complex in some cases. If you’re in a condo or apartment complex, you’ll need one for each unit. 

So, If you have only $300 or $400 to spend on earthquake preparedness and don’t want to put a single bolt into anything, please, oh please go get one of these. 



Got a question about home repairs and inspections? Send them to Matt Cantor at mgcantor@pacbell.net