A common piece of safety advice during an electrical storm is to take shelter inside a car. This suggestion often seems counterintuitive, as a vehicle is a large, metal object that appears to be a perfect target for a lightning strike. Many people believe the safety comes from the rubber tires insulating the car from the ground, but this popular idea is incorrect. The actual protection offered by a hard-topped, metal-bodied vehicle is a matter of physics and the way electrical charges behave around conductive enclosures. Understanding the true science behind this phenomenon can help you appreciate why your car is a temporary refuge during a thunderstorm.
The Faraday Cage Principle
The primary reason a car is safe during a lightning strike is the Faraday Cage effect, named after the 19th-century scientist Michael Faraday. A Faraday cage is a hollow enclosure made of a conductive material, such as the metal shell of a car. When an external electrical charge contacts this conductive shell, the charge is distributed across the exterior surface. This process ensures the electrical field inside the cage remains zero, effectively shielding the interior and its occupants. The lightning’s current, which can average around 30,000 amperes, flows entirely along the outside skin of the metal toward the ground.
This metal structure, not the rubber tires, is the sole source of protection. The idea that rubber tires insulate the vehicle is a myth, as the voltage in a lightning bolt is far too high for a few inches of rubber to act as an effective insulator. Since lightning has already traveled miles through non-conductive air, the resistance provided by the tires is inconsequential. For the Faraday Cage principle to work, the vehicle must have a complete metal shield; convertibles or vehicles with fiberglass or plastic bodies do not offer the same protection.
How Lightning Interacts with the Vehicle
When a lightning strike connects with a car, it typically hits the highest or most conductive point, often the antenna or the roofline. The electrical surge immediately flows across the car’s metal exterior, utilizing the path of least resistance toward the ground. This current remains on the outer surface of the conductor, bypassing the passenger cabin entirely. The charge then arcs from the lowest metal part of the vehicle, usually through the tires or the air around them, and into the ground.
While occupants are safe, the vehicle itself can sustain significant damage, including vaporized paint, melted antennas, and destroyed electronic systems. The intense heat and electrical current often travel through the steel belts in the tires, which can cause them to be blown out. A secondary risk known as a side flash can still occur inside the vehicle if an occupant is leaning against a conductive surface. If a person contacts both the metal shell and another conductive object inside, they can inadvertently become part of the circuit, providing the charge with the fastest route to the ground.
Essential Safety Precautions While Inside
To maximize the protection offered by the Faraday Cage effect, occupants must take specific precautions once they have pulled over.
Maintaining the Enclosure
Keep all windows and sunroofs completely closed to maintain the integrity of the conductive enclosure. An open window can disrupt the protective effect and create an entry point for the strike.
Avoiding Contact
Avoid touching any metal components within the car that are connected to the outer shell. This includes the steering wheel, door handles, radio knobs, gear shift, and electronic charging cables. Keeping hands in your lap and sitting away from the doors and windows minimizes the risk of a side flash.
Post-Storm Safety
It is advisable to turn off the engine and avoid using any built-in electronics to reduce the risk of electrical surges. After the strike and before exiting, wait until the storm has completely passed. The National Weather Service recommends waiting at least 30 minutes after the last rumble of thunder to ensure the immediate lightning threat is over.