Lightning Safety in Cars

1) is wrong. Lightning has just jumped across thousands of feet of a perfectly good insulator - air. It's not going to be discouraged by that 1/2 inch of rubber.

2) and 3) are correct.

4) is becoming correct as more and more cars are made from more and more plastic.

1. FALSE - an electrical discharge that propagates thousands of feet through air has no problem jumping a mere 4-6" around your tires to get to ground.

2. TRUE - but only if you have a metal bodied car. Protection does not extend to occupants inside fiberglass body cars or to rag tops (convertibles). Even in a standard metal bodied car, all bets are off if you have your arm sticking out of the rolled down window... :^)

3. FALSE - Most lightning discharges are unipolar, rapidly rising to a peak within hundreds of nanoseconds, and then decaying over tens to hundreds of microseconds. Several similar discharges may occur in close succession. Although di/dt is quite high (up to 10^11 A/s for negative CG), skin effect is really not why folks are safe within the car. They would be just as safe if a lower frequency source of high voltage briefly energized the body of the car - such as a power line. The occupants are safe because there's no internal E-field developed within the car - in a Faraday Cage.

BTW, because the peak currents are tens of kA (for negative CG - Cloud to Ground lightning) to 100's of kA (for positive CG lightning), if a person is directly struck the discharge will tend to flash over the skin due to the relatively high voltage drop "across" the person - people make relativley poor electrical conductors. The result is that lightning victims often exhibit branching Lichtenberg Figures (or "Lightning Flowers") on their skin in the areas near the surface discharge:

http://205.243.100.155/frames/human_LF2.jpg

4. FALSE - A metal skinned car is actually one of the safest places to be during a lightning storm, because of 2 above. Being inside a metal-bodied airplane is also quite safe for similar reasons. Both are much safer than being inside a wood frame house. This level of protection is not extended to being in a 'Vette or a convertable...

Bert

While discussing Lightning protection, sometime I wonder how lightning protection is adopted for Aircraft. I got some idea, anyone can put more light, is welcome.

I just happened to come across this recently while searching for lightning protection for space craft. Here's some info:

http://www.microsemi.com/micnotes/126.pdf

http://www.microsemi.com/micnotes/127.pdf

http://www.microsemi.com/micnotes/132.pdf

This has GOT to be the coolest scar ever!

http://205.243.100.155/frames/human_LF2.jpg

OW! Ow owowowowowowowowowowowowowow!

Question: If your in a fiberglass camper in the back of a metal pickup, are you at risk. The camper doesn't hang over the cab area, just the back.

Question: If your in a metal vehicle and touching part of the metal body while inside, do you become a conductor. Do you get killed? Just trying to figure out whether camping in an electrical storm is safe in this type of setup.

If there is no metal top on the camper that is also electrically connected to the truck body, then it is not safe from a lightning strike. Here's a paragraph from the Lightning Safety page on the National Weather Service (NOAA) site: http://www.lightningsafety.noaa.gov/wcm/lsawfull-2.htm

"The safest place from lightning readily available to most people is inside a large, fully enclosed building with wiring and plumbing, e.g. a typical house. But stay away from any conducting path to the outside: corded telephones; electrical appliances; and plumbing. Don't watch lightning from doorways or windows. If you can't get to a house, a vehicle with a metal roof and metal sides is a good second choice. Roll-up the windows, lean away from the door, and don't touch any conducting path going outside, e.g. radio, keys in the ignition, steering wheel, etc. Remember, it's not the rubber tires insulating you from the ground that make vehicles safe, but rather the metal shell that conducts the electricity around you -- convertibles, motorcycles, cars made of fiberglass and plastic, and open shelled outdoor recreation vehicles don't count."

The answer to your second question is a bit more complex, and depends on whether you are inside an all metal vehicle or in your fiberglass topped camper when lightning strikes.

1. If you're inside an all metal vehicle, the metallic body is really not a perfect Faraday Cage. During the main strike, the peak current may range from 20,000 (for negative CG lightning) to as much as 300,000 amperes (for positive CG lightning). The large di/dt and massive peak current flowing through the car's metallic skin can develop a significant voltage drop that appears across the vehicle's body inductance and resistance. If you happen to be contacting the interior of the metal body at multiple points, it is possible that you may experience a powerful (but most likely not fatal) electrical shock. Avoiding contact with interior metal surfaces avoids this situation. And obviously, you don't want to be using your CB radio (with the exterior whip antenna) at the time, since this could be fatal.

2. If you are in the fiberglass topped camper, lightning may penetrate the nonconducting top, then pass through you, the truck bed, and around the tires to get to ground. Being part of the main current path for a multi-million volt high current discharge is never a good thing...

Bert

It wouldn't be safe if the strike ignited the fuel in the fuel tank while the vehicle were occupied.

My understanding is that if you are going to be struck by lightning, the safest place to be is in a car. (Fraday cage) Best bet is not to be struck.

(I shall say this only once!)

This is how it was explained to me why you are safe inside a car during lightning strike:

When you are sitting inside a car, you are insulated from the ground because of the car's rubber tire. Because the car sit lower to the ground, when lightning hit it, it travels throught the metal body of the car and down to earth.

So, in that sense: 1) and 2) are both true.

MidniteFighter

You apparently didn't read (or choose not to believe) the earliest posts above.

#1 is PATENTLY FALSE!!! The insulating value of thousands of meters of air is many times greater than the rubber of the tires (or rubber shoes or rubber anything). Rubber is NOT an insulator, it is just a very poor conductor. But even the worst conductor in existence will, at some level, conduct if the potential across it is great enough and lightning is all about potential.

Let's do the math so that maybe you will put this silly notion behind you.

Air has a dielectric strength of 3 MV/m, so if for instance the lightning source is 3000m above the car, the lightning must have had a potential of 9MV to strike in the first place. Neoprene rubber has a dielectric of 12MV/m, but you have only maybe 2cm of rubber between the rim and the ground (assuming the inner surface of the tire is going to be conductive, which it likely is), so the tire insulating value will withstand .2 x 12MV = 2400V. 9MV potential, 2.4MV dielectric = conduction!

As was said earlier, IF you were in a car and a power line fell across it, you might be "safe" if the line was only 2400V. But be careful getting out of the car!

The metal cage of the car would protect you equally as well if it was sitting directly on the ground, or 10,000 feet in the air (airplane). The wheels, rubber or otherwise, have nothing to do with it.

I believe it's called a Faraday cage.

YES you feel it I Was hit On a major highway in Ontario Canada during quite a rain storm with a low profile sports car covering me . I smelled ozone and my teeth were tingling within 6 months all back teeth were dead. The car a burn spot on the spoiler and the alternator Trio pack the way my wife likes her toast black and crispy. The second time I experienced the charge of mother nature in a vehicle My whole family was in a van on another major hiway this time only the vehicle experienced it power dropped off then came back and a ball joint brake cylinder bearing on the front right gave up. Is a car safe in a lightning storm alot safer then you are facing it un protected. The more rubber under you and the higher you off the ground in a vehicle the better the insulation value.

A new study happening around Canada relating to lightning is "Is a cell phone a magnet for attracting lightning strikes" ?

Here we go again, relying on the old rubber will save me myth. Go play golf in a thunderstorm with rubber handled clubs, that should prove the point....

"The more rubber under you and the higher you off the ground in a vehicle the better the insulation value."

My goodness, what a bunch of blind (or illiterate) whackos posting on this site!

PAY ATTENTION!

THE RUBBER HAS NOTHING TO DO WITH IT!

<<<1) Rubber in the tires acts as an insulator to ground, and that protects you.>>>
Tyres of Vehicles as well as aeroplanes is not as INSULATOR as you think.

All the tyres have a % of carbon mixed up in rubber to avoid development of <Electro-Static> voltages due friction with road & helps regular discharge to avoid any Electrical-Arc after <Electro-Static> has gone to a dangerous level.

Somewhere in 1950s pure-Nylon tyres were introduced but soon withdrawn due to Electrostatic shock to riders/drivers on coming out of car.

Secondly Insulation of tyres [even if there is no carbon mixed] cannot hold in a season, when <Lightning> occurs [rain].
2.<<< 2) Metal frame of car acts as an Faraday Cage; hence no charge can pass through the cage.>>>
The Cage itself needs GROUNDING /EARTHING.
In rain almost all the body is having a good route to earth, even had the tyres GOOD_ INSULATORS.

The safest place to be when lightning strikes in your town, is another town.

Look, lightning is one of the most powerful forces in nature. There is no "safe" place to be, the effects and actions of lightning are for the most part, unpredictable. Rubber, distance off the ground, voodoo spells or tin foil hats are not going to do anything to protect you. A Faraday cage is helpful, but only to a degree, i.e. the conducting capacity of the cage. A car was NOT designed as a Faraday cage (although airliners are by the way), but it works somewhat like one, which is I suppose slightly better than nothing, and if I were caught in a storm without having a solid building to get inside of, a car would be my next best choice.

But the real value of the car is in taking me to the next town...