Lightning Strikes and Corrugated Stainless Steel Tubing
March 23, 2014| Von Mike Griffin
Region: North America
Lightning strikes cause 22,600 fires a year, resulting in approximately $407 million in damage. While the majority of lightning-related fires involve outdoor vegetation, most notably forest fires, there are also approximately 4,300 structure fires yearly and 73% of these structure fires involve residential homes1. The ignition source for many residential fires resulting from lightning strikes is corrugated stainless steel tubing (CSST) used for natural gas and liquid propane heating systems and appliances.
CSST was developed in Japan in the early 1980s and was first used in the U.S. in 1988. It became popular in Japan due to its flexibility and resistance to rupturing during an earthquake, unlike its predecessor black iron pipe (BIP), which is rigid and is apt to separate at joints during an earthquake. Although the material cost of CSST is more than that of BIP, it involves much less labor to install and the overall cost is about half that of BIP. It is estimated that CSST has been installed in 8 million homes in the U.S. since 1988, and about half the homes built each year contain CSST.
First generation CSST was very thin, .008”, or about the same thickness of a piece of paper, and identifiable by the yellow plastic insulation covering the pipe. An electrical arc resulting from a direct or indirect lightning strike can perforate this thin-walled piping. An indirect strike usually occurs when lightning strikes the ground near the structure and follows the underground gas pipe to the gas meter and then to the CSST. Lightning may also follow an electrical wire to the structure and then arc to the gas piping. Damage to CSST is identifiable by a small hole, often oval shaped, on a ridge of the CSST. The perforation usually results in ignition of the gas, creating what resembles a blow torch, which will ignite almost anything combustible in the vicinity of the flame.
Stainless steel has a very high melting point and in the event of a total loss structure fire, the insulation on CSST may burn off, but the tubing will remain intact and can be inspected for holes from a lightning strike that could have caused the fire. When first introduced, CSST was not tested for lightning resistance by manufacturers and electrical codes did not require grounding or bonding, as they do now. In 2009 building codes were changed to require grounding or bonding of the gas piping, which decreases the likelihood of arcing from a lightning strike.
The risk of fires from CSST presents a significant exposure to insurers but can be reduced by requiring that the CSST be properly grounded. Class action suits have been filed against manufacturers of CSST to recoup the cost of grounding the system. In addition, some potential sources of subrogation recovery for fires are: the manufacturer, contractor, electrician or home inspector.
Many of the approximate 8 million homeowners in the U.S. who have CSST in their homes aren’t aware of the risk of fire from a lightning strike. I wasn’t until I attended a recent seminar, at which Corrugated Stainless Steel Tubing fires was one of the topics, and I recognized the same gas piping I had in my home.
1. NFPA, Fire Analysis and Research Division, Lightening Fires and Lightning Strikes, Marty Ahrens, June 2013.