Car getting struck by lightning

[dEdt]

As we all know, if a car happens to be struck by lightning its passengers will probably be safe. The usual explanation is that the tires of the car are insulators. The actual reason, as E&M textbooks stress, is that the surface of the car, being a conductor, acts as a Faraday cage.

My question is, why would anyone think that insulating tires protect cars against lightning strikes? To be concrete, suppose that the surface of the car were made of an insulating material and therefore the car didn't act as a Faraday cage. Is there any reason to think that the insulating tires would protect the car? What's the justification behind this belief?

 

[dauto]

As we all know, if a car happens to be struck by lightning its passengers will probably be safe. The usual explanation is that the tires of the car are insulators. The actual reason, as E&M textbooks stress, is that the surface of the car, being a conductor, acts as a Faraday cage.

My question is, why would anyone think that insulating tires protect cars against lightning strikes? To be concrete, suppose that the surface of the car were made of an insulating material and therefore the car didn't act as a Faraday cage. Is there any reason to think that the insulating tires would protect the car? What's the justification behind this belief?

Are you seriously asking us why some people open their mouths and say things that are clearly wrong? People believe all sort of dumb stuff that they heard somewhere and never took the time to think about. Short answer: Lack of critical thinking.

 

[dEdt]

I guess what I'm asking is, is there a good reason to believe that insulating tires could protect a car, or is it just bad physics?

 

[dauto]

I guess what I'm asking is, is there a good reason to believe that insulating tires could protect a car, or is it just bad physics?

It's just dumb thinking.

 

[CWatters]

It's probably based on the idea that wearing rubber boots and gloves may help reduce your chances of dying while working on high voltage equipment. It's not the same though.

 

[Nugatory]

A
My question is, why would anyone think that insulating tires protect cars against lightning strikes? To be concrete, suppose that the surface of the car were made of an insulating material and therefore the car didn't act as a Faraday cage. Is there any reason to think that the insulating tires would protect the car? What's the justification behind this belief?

People are sometimes sloppy about the difference between protecting the car and protecting the people inside the car.

The insulating tires do reduce the chances that lightning will strike the car at all... but if the car is hit by lightning, it's the Faraday cage effect that helps protect the passengers from further injury.

 

[dauto]

People are sometimes sloppy about the difference between protecting the car and protecting the people inside the car.

The insulating tires do reduce the chances that lightning will strike the car at all... but if the car is hit by lightning, it's the Faraday cage effect that helps protect the passengers from further injury.

No, the tires offer no protection to the car. The lightning already jumped all the way from the cloud to the car. The extra little jump from the car to ground offers no protection.

 

[Nugatory]

No, the tires offer no protection to the car. The lightning already jumped all the way from the cloud to the car. The extra little jump from the car to ground offers no protection.

You sure of that? I've watched two objects of near equal height and a few tens of meters apart in a lightning storm and the one with the better connection to ground took more lightning strikes.

I do agree that if the car is sitting by itself with no more attractive target nearby, it's going to be toast, tires or no.

 

[dauto]

What do you mean by better connection to the ground? If the object is attached to a metal rod that has been buried deep into the ground and may be even had salts added to the soil and has an radioactive source on its top and a fairly pointy end (I've just described a lightning rod) than yes, you're correct. If the object is connected to the ground by just laying there on the ground than no, no added protection.

 

[dEdt]

What do you mean by better connection to the ground? If the object is attached to a metal rod that has been buried deep into the ground and may be even had salts added to the soil and has an radioactive source on its top and a fairly pointy end (I've just described a lightning rod) than yes, you're correct. If the object is connected to the ground by just laying there on the ground than no, no added protection.

Maybe this is a stupid question, but why would burying the metal rod deep into the ground increase the chance that it gets hit? I thought that lightning rods were buried in the ground so that the charge the rod picks us after a lightning strike can discharge safely into the Earth.

 

[UltrafastPED]

What do you mean by better connection to the ground? If the object is attached to a metal rod that has been buried deep into the ground and may be even had salts added to the soil and has an radioactive source on its top and a fairly pointy end (I've just described a lightning rod) than yes, you're correct. If the object is connected to the ground by just laying there on the ground than no, no added protection.

Around here it is always raining, often quite heavily, when there is a thunder storm; we get a lot of them at the northern end of "tornado alley".

It is the rain water that makes everything a conductor, even if it doesn't have roots deep into the ground. OTOH, I've seen several trees struck by lightning - it's quite dramatic! - while growing up on the farm. My father even saw lightning strike the ground at the local high spot, which is not very high around here, but taller than the house, and after the storm passed he found a large chunk of sand that had been turned to a glassy substance; looked like a large carrot with a couple of roots. This soil is from a glacial moraine, and is quite sandy, with little pebbles. Ordinarily you would think that it is a great insulator ... but not during a rain storm!

 

[berkeman]

People are sometimes sloppy about the difference between protecting the car and protecting the people inside the car.

The insulating tires do reduce the chances that lightning will strike the car at all... but if the car is hit by lightning, it's the Faraday cage effect that helps protect the passengers from further injury.

No, the tires offer no protection to the car. The lightning already jumped all the way from the cloud to the car. The extra little jump from the car to ground offers no protection.

One thing is for sure -- that car's radio is going to be toast, and maybe catch on fire. That nice pointy antenna sticking up in the air will make a nice target for the initial corona discharge.

I agree with duato that the insulation from the ground (via the [wet] tires) is not really going to help. I also agree that with many car designs, the Faraday cage effect will help to protect the passengers inside some. Not a place I'd like to be, though...

 

[berkeman]

Holy cow! This guy even volunteers to do some testing for us...

https://www.youtube.com/watch?v=ve6XGKZxYxA

 

[AlephZero]

Holy cow! This guy even volunteers to do some testing for us...

If you haven't come across "the hamster" before, he's fairly indestructible, as well as not understanding the concept of "risk".
https://www.youtube.com/watch?v=rCgbd81BTPE

 

[OCR]

Are you seriously asking us why some people open their mouths and say things that are clearly wrong? People believe all sort of dumb stuff that they heard somewhere and never took the time to think about. Short answer: Lack of critical thinking.

http://www.lightningsafety.noaa.gov/myths.htm

http://www.lightningsafety.noaa.gov/

http://en.wikipedia.org/wiki/Lightning

 

[D H]

For a more complete video, see http://www.huffingtonpost.com/2014/06/08/lightning-strikes-truck-video_n_5468879.html

 

[DTM]

It is often stated that it is a myth that a car's rubber tires help protect the car or occupants from a lightning strike. The fact is, the rubber tires do provide SOME protection and the reason is very important. If the car is struck, of course the metal "cage" around the passengers provide a safe place for them. But anything you can do to increase an objects resistance to ground will minimize the chance of an object being struck in the 1st place. It's often stated that if the lightning can jump hundreds of feet through the air, it can jump the last 6 inches through your tires. But this is a bad argument. The tires do hot have to have such a high resistance that lightning cannot go through them, they only have to have enough resistance so the car is not the lightnings path of least resistance. So a tree 50 feet away my provide an easier path to ground while if the car had steel tires, the car may have provided an easier path.

This concept is very important. A 1/4" of rubber on your hiking boots soles might be negligible relative to to the millions of volts of a lightning charge, but if it makes you a more resistive path than a nearby tree, they can protect you. ANYTHING you can do to increase your resistance (sit or stand on your pack) can help you in a lightning storm.

 

[FactChecker]

A 1/4" of rubber on your hiking boots soles might be negligible relative to to the millions of volts of a lightning charge, but if it makes you a more resistive path than a nearby tree, they can protect you.

That's like the old joke:
A bear jumps out of a bush and starts chasing two hikers. They both start running for their lives, but then one of them stops to put on his running shoes.
His friends says, "What are you doing? You can't outrun a bear!"
His friend replies, "I don't have to outrun the bear; I only have to outrun you!"

 

[FactChecker]

A 1/4" of rubber on your hiking boots soles might be negligible relative to to the millions of volts of a lightning charge, but if it makes you a more resistive path than a nearby tree, they can protect you. ANYTHING you can do to increase your resistance (sit or stand on your pack) can help you in a lightning storm.

It seems that there must be something more. If lightning wants to hit you, it can always hop to the side around your rubber soles. That is less than an inch of air to go through to get to ground, and probably not enough to make it strike somewhere else. It might be that the rubber soles stops a static charge from traveling from the ground to you and attracting the lightning. I can easily imagine the rubber stopping a static charge from building up in you.

 

[jerromyjon]

But then again if your feet are wet, you might as well be swimming...

 

[zoki85]

Is there any reason to think that the insulating tires would protect the car? What's the justification behind this belief?

The reason is probably based on tyres being good insulators at low voltages. At high enough voltage the arc will simply jump over their surface. Lightning is a multimegavolt phenomenon, tyres are pretty ineffective against it.

 

[Drakkith]

I'd think that the deciding factor would be the effect the tires have on the car's ability to generate an upward streamer to meat the downward leader from the cloud.

 

[zoki85]

I'd think that the deciding factor would be the effect the tires have on the car's ability to generate an upward streamer to meat the downward leader from the cloud.

Not sure. Short and relatively flat objects like cars don't generate upward streamers before downward lightning leader gets really close to the distance of last jump (ie. breakthrough phase). Maybe car on tyres has smaller chance to be hit than grounded car. However, Eriksson found that tall objects (vertical wires, masts) having small gap between it's base and ground had somewhat higher probabability to be struck by lightning than when they were earthed.

 

[DTM]

If lightning wants to hit you, it can always hop to the side around your rubber soles.

Yes, it can, but it will always take the easiest path (or paths). Often there are multiple paths to ground of similar resistances so that the lightning often splits and hits multiple spots during a strike. The paths with less resistance will see more current. Adding rubber, or an inch of air, to the path will add orders of magnitude to your resistance meaning less or no current through you. If you feel yourself about to be struck by lightning (which yes, you often feel the charge building up, your hair standing up, tingling, etc.) You should immediately stand on one foot, doubling your resistance. Many (and perhaps most) people who get struck by lightning survive, if you double your resistance and half your current, your more likely to survive.

 

[Drakkith]

DTM, that's a very simplified view of a lightning strike which I don't think works in real life. There are other things to take into account. For example, you may think that standing on one foot doubles your resistance, but you're only looking at a single part of the whole circuit. If you have a dozen resistors in series, doubling the resistance of one of these resistors does not double the resistance for the whole circuit, and the current flow will not be cut in half. There's also the fact that the electric field managed to ionize hundreds of feet of the air itself, so I don't think your quarter-inch rubber soles are going to put up much of a fight, especially when they starts heating up due to current flow.

 

[DTM]

Yes, Drakkith, my simplification was for the sake of argument, not meant for exact calculations. You're right about the series resistors argument. But once the air is ionized, that "resistor" has much lower resistance and I don't think a rubber boot becomes insignificant. Remember the boots don't need to be able to stop the lightning, they just need to be slightly more resistive than the next best path, which may be a tree 50 feet away. Then the lightning will take the easier path to ground. I work on high voltage electric machines, which exhibit corona discharge (mini-lightning @ ~50kV). Adding semiconductive caulk creates paths to ground reducing corona discharge in other areas. The analogy to hiking/camping would be to put up a lightning rod a small distance away from your high mountain camp. I don't know if any mountaineers do this, but it makes sense to me. I realized that last bit was a bit off topic, but bottom line I really think rubber boots or tires DO make a difference.

 

[Drakkith]

Remember the boots don't need to be able to stop the lightning, they just need to be slightly more resistive than the next best path, which may be a tree 50 feet away.

I'm not so sure. If this were the case, then few people would ever be struck by lightning thanks to modern footwear. (Not that many are struck by lightning to begin with...)

However, I did find this on the wiki article:

A huge surge of current creates large radial voltage differences along the surface of the ground. Called step potentials, they are responsible for more injuries and deaths than the strike itself.[citation needed] Electricity follows the path of least resistance. A portion of the return stroke current will often preferentially flow through one leg and out another, electrocuting an unlucky human or animal standing near the point where the lightning strikes.

So you may be correct in that standing on one leg can increase your chance of survival, but I don't think it's for the reason you stated. (Though citations appear to be needed)

You're right about the series resistors argument. But once the air is ionized, that "resistor" has much lower resistance and I don't think a rubber boot becomes insignificant.

There's also the resistance of the ground to take into account. The ground is far from a good conductor in many cases.

 

[DTM]

If this were the case, then few people would ever be struck by lightning thanks to modern footwear

I'm not saying good insulated footwear will stop all lightning from hitting people, but if you have a group of people hiking along a ridge, and one is wearing thin soled sneakers and the rest are wearing thick rubber boots, the guy with the sneakers is much more likely to get stuck then the other hikers. Of course if they're all hiking close together they will probably all be jolted, but the guy with the sneakers is more likely to be more seriously hurt. If there is a single hiker on the top of a ridge and even if he has super thick rubber soles, he'll get fried.

Here's a story of some hikers with trekking poles that acted as lightning rods, the opposite effect of the boots.

http://news.google.com/newspapers?n...LoojAAAAIBAJ&sjid=dYgFAAAAIBAJ&pg=3521,550783

 

[zoki85]

If you feel yourself about to be struck by lightning (which yes, you often feel the charge building up, your hair standing up, tingling, etc.) You should immediately stand on one foot, doubling your resistance. Many (and perhaps most) people who get struck by lightning survive, if you double your resistance and half your current, your more likely to survive.

Many people who don't get struck directly by lightning, but just stand in vicinty of struck objects don't survive. Standing on one foot (or feet brought close) helps in such cases becouse "step voltages" over corresponding points on the ground surface are smaller. If one get struck directly by lightning, standing on one foot will increase chance of survival by 0.001%

 

[OCR]

Here, read this... all of it.

http://www.srh.noaa.gov/jetstream/lightning/lightning_intro.htm

Finally, it's very common for the lightning to destroy one or more tires as it passes through the steel belts to the ground.

http://www.lightningsafety.noaa.gov/cars.htm

 

[DTM]

For anyone following but not having read through OCR's links, bottom line of the argument is this from about the 10th page down on the 1st link in FAQs
"Your ½" (or less) of rubber will make no difference."
But their rationale is this
" The average lightning bolt carries about 30,000 amps of charge, has 100 million volts of electric potential, and is about 50,000°F. These amounts are several orders of magnitude HIGHER than what humans use on a daily basis and can burn through ANY insulator"

Yes this 2nd quote is true, but this does not address my argument. Of course lightning CAN burn through rubber, but my argument is that if you are near other other things of similar resistance, your increased resistance will tend to force more of the charge to pass through other objects. I think these organizations such as NOAA make their information so resolute, and say rubber boots offer "NO protection" so they don't feel responsible if someone gets struck by lightning and they say, "I was outside during a lightning storm but I was wearing rubber boots and NOAA said they would make me safer".

I fully agree that rubber boots offer only minimal at best protection and should not be used as an alternative for the safe lightning advice NOAA provides, so as an organization I understand why NOAA has to says what they do, but as a Physicist, I have to say I think they are wrong.

Here's another example, let's say lightning strikes the ground x distance away. The shock that you feel will be decreased as x increases. So at some distance, the voltage between the charged ground and you will only be a few thousand volts, at another distance, it will only be a few hundred volts. So at these distances from the lightning strike, does anyone think the rubber in your boots won't make ANY difference? Of course it will make a huge difference. And based on the stats in the NOAA link, the vast majority of lightning strikes are non-lethal and so were likely not direct hits. Therefore thick rubber boots most certainly could have (or did) lesson the blow.

Am I wrong?

 

[DTM]

A similar argument can be made for why "duck and cover" is a good idea during a nuclear blast or meteor strike. Many people think advice to "duck and cover" during a nuclear blast is ridiculous. But it's not. Sure if you're within 2 miles (or whatever) of the detonation point, you'll be vaporized, duck and cover did nothing. If you're within 5 miles (or whatever) your building will be rubble and duck and cover did nothing. But if your between 5 and 20 miles, the shock wave blows out windows, and radiation goes through glass much easier than brick. Duck and cover can save millions of injuries. If the Russian's near their latest meteor strike had known to "duck and cover" when they saw the light flash of the meteor, instead of going to the windows, thousands of injuries would have been prevented.

And note that the area of minor damage (5-20 miles or whatever) is a much greater than the area of complete devastation. It's the same argument with lightning strikes, the rubber in your boots won't save you from a direct hit but it will minimize your shock from an indirect hit.

 

[Drakkith]

Yes this 2nd quote is true, but this does not address my argument. Of course lightning CAN burn through rubber, but my argument is that if you are near other other things of similar resistance, your increased resistance will tend to force more of the charge to pass through other objects.

And I don't agree. You haven't addressed how this effects the evolution of the downward leader's/upward streamer's ionization path, which is what decides the path the main discharge takes. You can't talk about this using simplistic ideas that normally apply in electronic circuits, as their are many different factors here, like insulation breakdown, radial voltages, and heating, some of which will be highly non-linear and not subject to idealized circuit laws. Regardless of how much resistance you might realistically have, once that streamer meets your or the ground near you, you are going to be struck and there's practically nothing you can do about it.

Here's another example, let's say lightning strikes the ground x distance away. The shock that you feel will be decreased as x increases. So at some distance, the voltage between the charged ground and you will only be a few thousand volts, at another distance, it will only be a few hundred volts. So at these distances from the lightning strike, does anyone think the rubber in your boots won't make ANY difference?

No one has said that. We aren't even talking about someone standing just on the edge of the lightning strike where the voltages are low enough that your boots can make a difference, we are talking about what decides the the strike location, which doesn't seem to depend very much on whether someone has rubber tires/boots or not.

 

[DTM]

You haven't addressed how this effects the evolution of the downward leader's/upward streamer's ionization path, which is what decides the path the main discharge takes.

When the charge builds in the cloud, and the ground charge is drawn to the highest points under the cloud (as in this picture).

The rubber in your boots or car tires will minimize this flow. The charge will go up other nearby objects that aren't so well insulated from the ground. Therefor the streamers will more likely ionize along other paths.

 

[DTM]

No one has said that. We aren't even talking about someone standing just on the edge of the lightning strike where the voltages are low enough that your boots can make a difference,

Many many science organizations say things such as "Your ½" (or less) of rubber will make no difference" when discussing outdoor lightning safety. I'm saying it DOES make a difference. If another person is standing 50 feet away on a flat open field, and you have rubber boots and he is barefoot, the charge from the ground will travel up his body more than yours and the streamers and lightning will travel through the barefoot person, if not exclusively at least more than you. And if it strikes the ground between the two of you, he'll get more of a shock then you.