I am writing this on Sunday as some residents are being allowed to return to their homes not knowing what they will find. If their home is livable they have a place to live, but their lives will be changed forever.
What caused this great disaster is still under investigation what we know is a 30 inch high pressure gas transmission pipe line developed a leak and ignited. Why it developed a leak is unknown at this time, possible causes are corrosion, electrolysis, ground movement, earthquake or all of the above. What happened in San Bruno happens everyday in homes across the United States. While we don't have 30 inch gas lines in Our homes we have gas pipes that feed Our stoves, furnaces, water heaters and the like. Gas piping generally last a very long time. But they do Leak!!
When a gas pipe leaks within a home it generally is silent, the only way you would notice a leak is the smell that is added to gas to make it noticeable (Rotten Eggs) or a higher than normal gas bill. While the gas pressure in a home is approximately 1/2 pound it still can create a Life changing explosion. My first experience with this was in 1962 when my best friend's House Blew Up!!! Luckily everyone made it out without being hurt. The force of the blast was so great it actually lifted the entire roof and framing off the house. Sal and his family could not live in their home for about six months while it being rebuilt.
Most gas leaks are caused by corrosion, improperly installed gas piping and movement of some sort. Most gas piping within a home is made of black steel pipe with tapered threaded joints if the piping is subject to water or dampness it will corrode very quickly eventually causing a leak. Galvanized pipe is black pipe that has been electro-plated with zink to resist corrosion and is generally used outside the building above ground. The threaded tapered joints I mentioned earlier usually have the bare metal exposed and are where most leaks occur, not because the rust through because of the threaded joint has failed due to vibration or movement or poor workmanship. A improperly installed gas pipe were the pipe is improperly supported or the joint is strained may not leak right away,but after years of expansion and contraction from temperature changes may leak without notice. Earthquakes shake and twist everything, a gas joint is no match for Mother Nature.
The good news is that new gas line materials are proving to be better and last longer. High Density Polypropylene is a type of plastic gas pipe that is used underground that uses fusible joints that are as strong as the pipe itself and does not corrode. A gas line material called Corrugated Stainless Steel Tubing replaces steel piping within houses. The new material called CSST for short is vinyl coated and is flexible, being flexible it means less joints and should handle movement better.
What can you do to protect yourself and your Home?
1) IF YOU SMELL GAS, or if you have any doubts, open windows and doors and get everyone out of the building. Using a phone away from the building, call 9-1-1 and Your gas supplier
2) Install a automatic earthquake gas shut off valve
3) Only use a professional plumber trained in gas pipe installation, repair and leak detection
4) Have your gas piping visually checked for corrosion painting may be required.