Third in a series of articles about earthquake preparedness.
For residents in California and other seismically active regions of the county, the word “earthquake” conjures up frightening news footage images of toppled walls, collapsed roofs, and cracked foundations. As disturbing and devastating as these damages are, there is another type of damage that is perhaps equally (if not more) dangerous and yet most people don’t associate it with earthquakes – fire damage from gas leaks.
It’s well documented that following major seismic events, leaks from ruptured gas lines have resulted in enormously destructive and often fatal fires. Archives dating back to the historic 1906 San Francisco Earthquake recount that leaking gas was the catalyst for the massive fires that raged for three days and destroyed over 500 city blocks. In more recent times, an in-depth study of earthquake-related fires following the 1994 Northridge Earthquake found that over 70% of the fires occurred in residential structures, and escaping natural gas was the single most common ignition material.
Reducing the Risk
The good news is that this potentially catastrophic hazard can be largely prevented by installing an automatic gas shutoff valve (AGSV). Following the Northridge Earthquake, a handful of California cities and counties passed laws requiring AGSVs on most buildings, and more states and municipalities may consider similar legislation. But despite the well-established risks and the obvious benefits, many residential structures are still not equipped with AGSVs.
As an essential part of an earthquake preparedness plan, AGSVs should be installed by a professional plumber or contractor in earthquake-prone areas. While there are many makes and models of approved automatic gas shutoff valves, most fall into one of two categories based on how the valves function:
- Seismic Gas Shutoff Valve (SGSV) – SGSVs are typically 3- to 5-inch solid metal casings that are installed either vertically or horizontally on gas lines. They have an internal mechanism that immediately stops the gas flow if it senses a significant tremor or shaking (usually at least 5.2 on the Richter scale). SGSVs are available in a wide range of sizes to accommodate gas lines from ¾ inch to 8 inches, which make them more favorable for larger houses (> 3,000 s.f.). Most SGSVs have a manual reset feature to restart normal gas flow.
- Excess Flow Valve (EFV) – Most EFVs are 2- to 4-inch metal or PVC fittings that are installed vertically on the gas lines. Once installed, they can be somewhat difficult to identify as they essentially become part of the gas line. Rather than sensing motion, the EFV’s internal mechanism senses sudden increase in gas flow (e.g., from a ruptured gas line) and restricts the flow to a minimum. EFVs are generally installed on ¾- to 1 ¼-inch gas lines and ideally suited for relatively smaller houses (< 3,000 s.f.). Once the gas flow returns to a normal rate, EFVs automatically reset themselves.
For more ways to protect your home against earthquake damage, don’t miss our series of blogs about earthquake preparedness.
Joe Kim is a Premier Account Specialist with Chubb Personal Risk Services’ Risk Consulting Group.