The chance of an individual building being struck either directly or indirectly (nearby lightning strike) is based upon the geographical location and the topography of the site. Check the Vaisala Lightning Explorer to see a live map of US lightning events.
According to insurance industry sources, there were 185,000 lightning claims in 2009, which was down from the five year average of 226,000. However, there are, on average, 4,600 lightning fires to residences in the United States each year, so the chances of a lightning fire are very low. It is common for lightning to exceed 100,000 volts and 40,000 or more amps. The current induced by a lightning strike does NOT “take the path of least resistance” as popularly believed. Current from lightning takes ALL paths to ground.
Lightning energy that enters a building during a nearby strike 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.
Arcing is very likely to cause damage to mechanical and electric systems. This same phenomenon is one reason that sensitive electronic equipment within buildings is protected by lightning surge arrestors.
Lightning can cause significant damage directly, by striking the building, or indirectly, by electrical currents igniting structural parts or systems within the house, which could cause further damage. Electrical wiring is the system most often damaged by lightning. Due to its low insulation value (600 volts), common household wiring can be easily breached by arcs caused by high lightning voltages. Once the insulation is damaged by that arcing, it is possible for electrical wiring to cause fires by further arcing of the household current, or contact with flammable materials that are close to the damaged wiring.
Similarly, gas piping systems convey flammable gas fuel that may add to the fire hazard if any system components—including valves, regulators, and appliance connectors—are damaged. However, this is not a recent phenomenon. Black iron piping systems—as well as copper tube and the newer corrugated stainless steel tubing (CSST)—can all be compromised by nearby strikes causing electrical arcing and damage to components.
Leakage of fuel gas from a gas piping system (iron, copper, CSST) damaged by lightning can cause a fire.