I was listening to the news a few days ago during a very bad storm where there were trees falling, trash cans blowing, and power lines falling all over the place. As I have now heard multiple times while watching the news or weather during a storm, they warned people to be careful of downed power lines. They said specifically that people should stay away and call Consumers Energy if they were to see a downed power line. They also mentioned that if you are unfortunate enough to have a power line come down onto your car (or if a downed power line touches your car in any way) you should not leave your car because you are safe within your car, but could die if you try to get out.
This is perfectly true, but not for the reason we are always told. On this occasion, the reporter made no mention of why people should stay in their cars, but it is quite common to hear an incredibly incorrect reason. News/Weather people always tell you to stay in your car, but normally tell you it's because the tires insulate the car from being grounded. This is ridiculous for two different reasons.
Firstly, high voltage electricity is not nearly as afraid of rubber as the electricity running through the wires of your headphones is. Guess what? Lightning and electricity from high voltage power lines has enough potential energy that your tires are really not that big of an obstacle. Have you ever heard of fulgurites? They are also called lightning glass. Fulgurites are the objects that are formed when lightning strikes sand and actually melts the sand into glass. Sand (and glass) is not a good conductor, but is in fact a relatively good insulator. So how did the lightning go through it? Also, think about what one of the most common outdoor objects to get struck by lightning is……Trees! Wood is another material that is a terrible conductor of electricity, but it is very common that lightning will go through trees to get to the ground. Lightning has enough energy that it can go through just about anything it wants.
You could think about this much like thinking about different vehicles at things that would normally block them. If you drive your Ford Escort at a cinderblock wall going maybe 30mph, you will not get through it. However, if you drove an M1A1 Abrams tank into that same wall (at the same speed), I'm guessing the wall would not be that big of an obstacle. The same is true of high voltage electricity. Your Ford Escort is like the electricity from a 9V battery and the Abrams tank is like lightning or a high voltage wire. You are more used to dealing with the 9V battery, so in your experience, you can't just drive through a wall, but high voltage electricity can break the rules of your normal experience.
The second reason that this particular reason of why it is safe to stay in your car is ridiculous, is because of the simple issue of whether your car is grounded. Your car not being grounded does not make you safe inside your car or outside your car. Really, you would be much better off all the way around, if your car simply were grounded. If it were grounded, the car would not hold any electrical energy within the body and frame and you wouldn't need to worry about being electrocuted. All the electrical energy would simply flow through the car and into the ground, if it were grounded. If the rubber of your tires wasn't present, you would be in great shape because all the electricity would already be through your car and into the ground before you were even able to process what happened. The reason it is not safe to get out of your car is related to the car not being grounded, but it has nothing to do with why it is safe to stay in the car.The real reason of why you are safe inside your car when it gets electrified has nothing to do with grounding and everything to do with the nature of electricity and the 3-dimensional shape of your car. Electricity is simply the flow of electrons (negatively charged, subatomic particles) through a material. Materials that easily allow electrons to flow through them are called electrical conductors and things that do not are call resistors (or insulators). You probably learned at least a little about electrical charges and magnets and stuff in elementary and middle school and really, that is all the information you need to understand what goes on with your car. When your car is electrified, what that means is that there are tons of extra electrons just hanging out in the metal frame and body. We learned in middle school that all electrons are negatively charged and that things of the same charge repel each other. From this we can infer that all the electrons now residing in the metal frame and body of your car are all trying to get as far away from each other as possible. Since your car is generally kind of a 3-dimensional hollow oval shape, the best way for the electrons to get away form each other is to line the outside surface of the 3-dimensional oval shape. If the electrons were to line the inside of the oval, they would have to be closer together than if they were on the outside and they don't want to be closer together. Now, obviously your car is not actually an oval, but the principle works exactly the same way for the more complicated shape of your car.
So, when your car gets electrified, all the electrons from the high voltage power line or from the lightning will line the outermost surface of your car because they are all repelling each other. This means that there are no electrons on the inside of your car so that is where you want to stay. If you stay inside your car, you are safe because all the electric charge is on the outside of the car and not near you. If you get out of the car, as soon as you touch the ground, you would provide a path for the electrons on the outside of your car to get to the ground through you. This would be a very bad situation and would most likely kill you.
I would like to reinforce the fact that it is a terrible idea to get out of your car if it has been either touched by a power line or struck by lightning. It is highly unlikely that you would be able to get out of your car safely (i.e. without dying) after it has been electrified. There are a few, very limited situations in which it would be reasonable for someone to try to get out of their car while it electrified. If, for instance, a power line falls on your car while you are stalled on railroad tracks and you can see the train coming, you need to get out. If for some reason you need to get out of your car (need = there is no reasonable chance of living if you don't get out) after it has been electrified, you should get out by jumping and trying not to touch the ground or anything else until you are as far away from the ground as possible. I would recommend trying to get onto the top of your car somehow and jumping hard enough and far enough that you almost certainly hurt yourself badly when you do hit the ground. Even if you jump from your car, there is high likelihood that the electricity will jump to you and then to the ground once you land, so absolutely do not attempt this if you do not need to.
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