If you’ve ever run black pipe to deliver natural gas to a combustion appliance such as a furnace or water heater, you won’t have any trouble seeing the beauty and convenience of a product that installs much like PEX, but that is used for natural gas and propane. Unfortunately, the very flexibility of CSST product also appears to be its vulnerability.
Since the corrugated stainless steel material gains flexibility by being very thin, it is vulnerable to electrical surges such as those created by lightening. The lightning can melt the CSST and release natural gas into the house where the fuel can reach an explosive concentration quickly. Methane becomes potentially explosive when it is 5% of the atmosphere . . . propane at only 2.1%.
I’ve been following the possible problems with CSST since at least 2007, when NY State code added language to the effect that the flexible piping should be electrically bonded. Only a few houses that I have been in since that regulation was adopted have complied with it, and this has worried me to some extent. Now it appears that bonding cannot protect the gas delivery system from nearby lightening strikes.
Raters and builders as well as pretty much everyone in the industry need to be aware of the potential problem with this material and to think carefully about having it in their projects.