~ National Lightning Safety Institute ~

Vehicles and Lightning

What happens when lightning strikes a vehicle? The answer, gleaned from anecdotal observations, is all the way from "Nothing" to "Wow! What a mess . . . my car is a disaster."
Electrically speaking, at lightning's higher frequencies, currents are carried mostly on the outside of conducting objects. A thick copper wire or a hollow-wall metal pipe will carry most of the lightning on outer surfaces. This phenomenon is called "skin effect." The same holds true for lightning when it strikes metal vehicles: the outer surface carries most of the electricity. The persons inside this steel box can be likened to protected by a partial Faraday cage.
But, consistent with lightning's capricious nature, situations alter results. Is the car dry or wet? If the car is made of fiberglass (a poor conductor) or a convertible, skin effect principles may not work. (Corvette and Saturn owners, please note this fact.)
Some general recommendations include:

  1. Personal Safety Issues. Reported incidents and related injuries make it clear that a person inside a fully enclosed metal vehicle must not be touching metallic objects referenced to the outside of the car. Door and window handles, radio dials, CB microphones, gearshifts, steering wheels, and other inside-to-outside metal objects should be left alone during close-in lightning events. We suggest pulling off to the side of the road in a safe manner, turning on the emergency blinkers, turning off the engine, putting one's hands in one's lap, and waiting out the storm.
  2. Heavy Equipment. Backhoes, bulldozers, loaders, graders, scrapers, mowers, and other heavy equipment that employ an enclosed rollover systems canopy (ROPS) are safe in nearby electrical storms. The operator should shut down the equipment, close the doors, and sit with hands in lap, waiting out the storm. In no circumstances during close-in lightning should the operator attempt to step off the equipment to the ground in an attempt to find another shelter. Very dangerous step voltage and touch voltage situations are created when a "dual pathway to ground" is created. Lightning voltages will attempt to equalize themselves, and they may go through a person in order to do so.
    Smaller equipment without a ROPS is not safe. Small riding mowers, golf cars, and utility wagons are examples of unsafe vehicles. Rubber tires provide zero safety from lightning. After all, lightning has traveled for miles through the sky: four or five inches of rubber is no insulation whatsoever. People should safely abandon this machinery and get into a safe shelter.
  3. School Buses. Metal buses are good Faraday cages. Make sure all windows are closed and the "hands on laps" rule is observed. Pull over and wait out the storm.
  4. Damage. Reported damage to vehicles includes pitting, arcing, and burning on both exterior and interior places. See the photographs below, courtesy of Mr. Brown, of his Jeep Cherokee that was struck by lightning. Cases have been reported of total destruction of vehicle wiring, and associated electrical and electronic systems. Cases from police departments report bad burns to the hands and mouth where officers were using radio microphones when their vehicles were struck. Cases describe total blow-out of all four tires in passenger cars. A video in our NLSI library shows a station wagon being struck by lightning in a heavy rain storm, with no damage whatsoever occurring.
    Insurance adjusters and claims people note: In many cases you will not find physical damage. Lightning can induce indirect effects to a vehicle's electrical and electronic systems. These low-voltage components may be damaged or destroyed. Auto dealer diagnostics are limited to "it works or it doesn't work" without the ability to disclose the cause or source of malfunction. Sometimes a claims decision may have to be based upon "What else — other than lightning — could have done the damage?"

Strike near hatchback / Close-up of strike / Strike at roof

Museum of Science: Touching Lightning

During part of our regular lightning shows the demonstrator raises the cage so that it will be struck by the sparks. We do this to demonstrate why it is safe to be in a car during a lightning storm. Most people believe that the reason has to do with the rubber tires, rubber being an insulator. Air is also an insulator, however, and almost as good a one as rubber! If a lightning bolt has just traveled two or more miles through air, an inch or two of rubber will not make much difference. Indeed, it has been calculated that you would need solid tires about a mile thick to be safe!
However, that is not needed as there is a more effective protection involved. In a car you are sitting in a metal box (this is not true in a convertible or plastic/fiberglass car, and these are not safe). That is the source of your safety. Many people who know that it is the metal not the tires assume that the car forms a Faraday Cage, but that is also not the reason. Faraday Cages work with static electricity, lightning bolts are anything but static! The real reason is something called the skin effect.
In fact, not only are you safe inside the car, even the inside of the metal car BODY is safe, a fact we demonstrate by touching the inside of the cage bars while it is being struck. The outside is not safe, however, so if your hand were to go through the bars you would get struck (something that has happened to several of us at one time or another--it hurts a lot, like hitting your funny bone but about ten times worse--though the current is so low that there is no permanent damage. The hardest thing for the demonstrator in such cases is to remember not to say something bad since the microphone is still on!