Risk Of Lightning-Based Fires With CSST Gas Lines
RISK OF LIGHTNING-BASED FIRES WITH CSST GAS LINES
By KPE Investigative Engineers
CSST, or corrugated stainless steel tubing, is a type of tubing used to transfer natural gas to home appliances. CSST is meant to be a more flexible and lighter replacement for typical rigid black iron pipe which is found in many homes. While it is much more expensive than black iron, CSST allows for easier installation and more customized tubing layouts. However, black iron pipe has much thicker walls than CSST. Specifically, CSST has walls which are 10 mils or thinner while black iron pipe is closer to 120 mils thick.
CSST has been installed in over 2 million homes in the United States since it became available for commercial use in 1988. Since the inception of CSST’s use, there have been an increasing number of recorded cases of home fires from the damage caused to CSST gas lines as a result of lightning strikes. For example, in Carmel, Indiana there were 6 fires related to CSST in just two years. The CSST gas lines contacted by lightning often develop small perforations, around 100 mils wide, in the wall of the tubing when the lightning arcs from the CSST to an adjacent object.
This arcing burns a hole in the CSST which causes a gas leak and, in many cases, ignition of the gas which leads to a house fire. The reason for CSST’s susceptibility to failure through arcing is the wall thickness. In cases where black iron pipe has been subjected to arcing from lightning, there is often only a small crater in the wall which does not cut deep enough to cause a gas leak.
In the case of a house fire in Nebraska, a fire was caused by a failed CSST line perforated by an arc from a lighting strike. It was determined the ground wire for the CSST was not correctly installed so the electricity from the lightning strike, instead of flowing to ground, flowed through the steel wall of the CSST and caused the failure.
The incorrect installation of a ground wire was determined to be the cause of many other fires in homes with CSST gas lines throughout the United States. Inconsistent installation standards among different installers are believed to be the cause of such problems. While the gas line is typically installed by the plumbing contractor, grounding is typically done by the electrical contractor. Many times the grounding of the gas line is overlooked.
In 2007, a class-action lawsuit against four CSST manufacturers was settled by an agreement that these companies, and later a few others, would reissue more thorough and clear bonding and grounding instructions for their CSST products.
The National Fuel Gas Code (NFPA 54) is the primary source covering installation of natural gas systems. The National Electric Code (NFPA 70) also has requirements for bonding metal gas pipe. Neither code explicitly calls out who is responsible for grounding. A contractor who is qualified should install the bonding clamp and conductor. In many jurisdictions, this is considered electrical work and requires a permit to be pulled. However, it is not uncommon for the HVAC or plumbing contractor with a limited electrical license to do the work. Until there is coverage within the NEC, CSST installers and electrical contractors are cautioned to get local concurrence regarding the direct bonding of the CSST from the Authority Having Jurisdiction (AHJ). The question of who performs the grounding depends on several factors:
- Stage of construction (new vs retrofit)
- Local licensing requirements for trades
- Local plumbing and electrical codes
- Opinion of local building officials
Until the NEC is updated, the CSST installer is ultimately responsible to insure the bonding is installed in accordance with local code.
According to a recent article, “Whose Job Is It to Bond Corrugated Stainless Steel Tubing (CSST)?” by Beck Ireland published in Electrical Construction and Maintenance, the latest information regarding the update of the NEC is as follows:
The NEC requires bonding of gas piping but the focus appears to be on hazards from the building electrical system, not lightning.
An excerpt from the article reads, “Proposals to include specific bonding requirements for CSST gas piping systems in the 2011 NEC were rejected by NEC Code-Making Panel 5 on the grounds that lightning protection for gas piping systems is beyond the scope of the NEC. “The mitigation of the effects of lightning is a design option,” reads the rejection. “The purpose of the NEC is the practical safeguarding of persons and property from hazards arising from the use of electricity.”