Lightening - safer inside a car?

[smudge]

I don't mind thunder, but I am terryfied of lightening. Is it true that the safest place to be when lightening, is inside a car?

[theo_wyvern]

one of the safest yes - metal acts as a big conductor - tyres don't insulate it because metal is close enough to the ground. however if it happens best to keep away from anything metal in the car, so hands and legs tucked in best you can to make sure

[smudge]

Thank you for that theo. So where would the 'safest' place be, do you think?

[sideymun]

I don't know if its the safest place but its definitley where i'd take shelter! The car's metal chassis acts as a Faraday Cage which renders the inside of the car fairly safe. The basic concept of a Faraday Cage is that it safely diverts any electricty around the outside surface of the cage. The important thing about the cage is that no current will be transferred into the cage. In this way anything inside the cage is protected from the electricity outside.

Unfortunately a car is not a perfect cage and so this is not the only thing that protects you. The fact that you are insulated from the ground by 4 rubber tyres prevents you from grounding (earthing) yourself and so there is no complete circuit thru you within which current could flow and cause you damage. Obviously if you decided to hold onto the metal body of the car with one hand and a cable(metal rod) to the ground with the other the benefits of the car would destroyed as you now form a complete circuit and are in for a shock.

I wrote this answer from memory so hopefully i've not made any mistakes...anyone is free to correct me!

[smudge]

Thank you sideymun, I'll try to remember that next time I'm tootling along in my car in a storm! Uurrgg!

[cupra]

Don't tyres contain carbon (a conductor?)

[New Forester]

sideymun - your memory looks good to me... However, I'd agree with theo_wyvern that at lightning voltages the rubber tyres do not provide significant insulation. This is a spark which can jump half a mile -- a few inches of rubber or air beneath the car are not going to be much barrier! Likewise it's not going to need a metal rod to connect you to the ground -- just waving your hand out of the window towards the ground might be enough. However the care is more likely to earth by a spark jumping from the underside.

[smudge]

Thank you New Forester - I shall remember not to open the windows & wave my hands about outside the car when in a storm!

[Doolallygirl]

Ok so say your car does get struck by lightening, then what do you do? If the car becomes a cage how do you get out?

[jenstar]

Another factor in favour of taking shelter in a car is that cars are quite low to the ground, and lightning tends to strike higher points.

[sideymun]

Doolallygirl, there's no need to worry. The car will only acts a cage for the brief time during which the lightening is striking the car. So as soon as the current finds a route to earth, the car will no longer act as a cage and you can safely get out.

[sideymun]

New Forester and theo_wyvern, having woken up a bit (and had several coffees) since i wrote my earlier answer this morning i have to agree that the rubber in the tyres would offer very limited protection from a lightening strike. New Forester i would also agree that the car is most likely to discharge via its underside - its likely to be the easiest path for the current to flow to earth.

[Doolallygirl]

Phew thank god for that! I just had images of a horrible storm rolling overhead, getting in my car and then being struck by lightening and made to stay there until some passer by found me a few days later!! (Obviously in my thoughts I'm in the middle of a field!!)

[DrWu]

This was recently covered on Top Gear. They had Richard Hammond inside a VW Golf and fired artificially generated lightning at the car for a good minute or so. Both he and the Golf were fine!

[smudge]

Thank you DrWu, you have put my mind at rest now!

[Maxrom]

One thing to check however, is that you don't have one of those anti static straps hanging off the back of your car that touches the ground. If you do, this would form a perfect conductor, and negate any protection you might have from being elevated off the ground upon rubber tyres.

[JohnLIreland]

I was just clarifying something on the insulating effect of tyres in a lightning strike and and read this. It's a bit late, I know, but I'm sorry Maxroom, the reverse is true. You want the lightning strike to discharge and dissipate so an anti-static earthing strip would assist this process. A Faraday cage only works correctly if it is earthed or the charge can eventually get to earth. The farther it has to go, the larger the charge needs to be to jump the distance so the bigger the power build-up will be.

[JohnLIreland]

Just to answer the question from Cupra, yes the carbon is a conductor BUT it is embedded in rubber, a good insulator, so the conductivity is marginal. That's why you get a static build-up in a moving car as the static doesn't dissipate quickly enough when you stop rolling so, sometimes, you get a small shock when you touch the bodywork and the ground, i.e. ground the static charge to earth.