I get this question a lot, usually from someone angry that I said their CSST was not bonded properly. Electricians especially get annoyed with me, so let me take a bit of time and explain CSST and why it keeps popping up in (my) inspection reports.
First, the acronym, CSST, stands for Corrugated Stainless Steel Tubing. This piping is used to transport gas within your home from point A to point B. Simple enough. The physical appearance is a flexible yellow hose-like gas line. The flexibility is one of the major benefits of the piping, eliminating the need to create seventeen turns in the line to get to a specific fixture such as the gas fireplace or stove. This reduction in installation expense compensates for the increased cost of the CSST. Black iron pipe is still cheaper; labor is still expensive, so CSST has earned a solid niche in the building industry. the reduction in fitted connections subject to gas leakage cemented the deal. Builders and code officials alike approved of Corrugated Stainless Steel Tubing.
However, since its introduction into the marketplace in 1990, we have learned a few things about CSST. The most important for me as an inspector is that CSST, while safe under almost all operating conditions, has one issue that necessitates special attention. That condition is an over-charge of electricity along the gas piping. Under those conditions, such as a close proximity lightning strike, the energy travels along the black iron and, when it reaches the CSST, can cause a failure in the flexible piping that creates a fire.
By 2005, a class action lawsuit was brought against the manufacturers. By 2006, with the winds blowing against them, the manufacturers voluntarily agreed to modify their bonding requirements to ensure that the unlikely event of a fire became a remote possibility. In 2009, the voluntary bonding entered the building codes, in both the International Residential Code (2411.1.1) and the International Fuel Gas Code. Quoting the former, "G2411.1.1 (310.1.1) CSST. Corrugated stainless steel tubing (CSST) gas piping systems shall be bonded to the electrical service grounding electrode system. The bonding jumper shall connect to a metallic pipe or fitting between the point of delivery and the first downstream CSST fitting. The bonding jumper shall be not smaller than 6 AWG copper wire or equivalent. Gas piping systems that contain one or more segments of CSST shall be bonded in accordance with this section."
Seems clear. One problem. It's in the IRC and not the National Electrical Code (NEC). Almost every municipality uses the NEC for their model code and this is the standard that electricians adhere to. The pipe fitters, at least in Washington, believe that they are prohibited from making this bonding connection as it may qualify as electrical work, while the electricians are unaware of the need for the bond. The end result is confusion when the home inspector properly identifies the CSST as lacking the proper bond.
According to industry estimates, there is about a billion feet of CSST installed, and much of it is in need to retrofitting.
If you want more information regarding bonding to share with your electrician, go here.