The scientific and technical details by which lightning can energize metal systems inside a building and potentially start a fire are very complex.
No gas piping product is immune to the damage caused by a direct lightning strike (refer to NFPA 780 for lightning protection systems for buildings and building systems).
Indirect lightning strikes can affect all metallic mechanical systems, including all forms of gas piping, when lightning energy enters a building during a nearby strike. Lightning has been shown to energize the metallic systems in a house through impressed voltage and induced voltage. Once this energy is inside a building, it will seek to return to ground along every possible path. In an attempt to equalize potentials, the energy may jump or arc from one pathway to another, depending on the electrical resistance of the material. This arcing is very likely to cause damage to mechanical and electrical systems.
For example, compare CSST to Romex® or NM electrical wiring. Electrically, they have many things in common:
Both are installed in homes.
Both have insulation over medium-carrying metal components.
Both carry dangerous substances that can cause fire and personal injury.
The insulation in both can be damaged by lightning.
But they also have differences. The National Electrical Code (NEC) requires standard NM wiring to have an insulation value of at least 600 volts. This is plenty of insulation for household current. But it is no match for lightning. If lightning energy enters the structure, it can overwhelm all metal systems including the electrical wiring, and will cause arcing between the electrical wiring and other metal components in the building. In contrast, CSST has a plastic jacket with an insulation value of at least 24,000 volts.
Furthermore, if lightning energizes the electrical wiring, the circuit breaker or fuse will not trip fast enough to interrupt the power to an NM wiring circuit. The current flow in a lightning strike is measured in microseconds (millionths of a second), whereas a circuit breaker will trip in 1/10th to 3/10ths of a second. Thus, lightning current can damage the electrical wiring by arcing and allowing electricity to flow and ignite other materials.
According to a major lightning consultant, 80% of lightning fires originate from damaged electrical wiring. In fact, it is possible for the arc from electrical wiring to be maintained with a current of 10 amps flowing from the electrical system—which is below the rating of the lowest rated circuit breaker.
The design of CSST piping is much more robust than electrical wiring in resisting damage from lightning.