Car getting struck by lightning

[Drakkith]

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.

I'm sorry but an extremely simple picture and a claim using very basic circuit laws is not enough to support your position. As I explained, the ionization path is not a simple circuit and you cannot just apply the laws out of context.

 

[DTM]

Drakkirth, You are right that simple circuit laws do not fully explain lightning phenomena. I wouldn't claim to be able to calculate the exact current through a person with and without rubber soles. But the laws of physics still apply to charge flow. Increasing the resistance of a path to a person's head by adding rubber to their feet will significantly reduce charge flow. Especially when you can increase the resistance by orders of magnitude which a 1/2" of rubber will do. Saying it doesn't matter is like saying a lightning rod will work as well if you attach it to a piece of rubber instead of driving a metal rod into the ground.

Since this phenomena isn't fully understood by the scientists in the field, I doubt either one of us could prove the other wrong analytically. I'd love to have the Mythbusters test this one. One dummy with rubber boots and the other with bare feet, and see which gets struck more in a lightning storm.

 

[DTM]

I found this.

from the National Outdoor Leadership School. Explains how ground currents kill 50% of those killed by lightning. This supports keeping your feet together (or stand on one foot). And I think clearly (though not explicitly) shows that rubber boots would make a difference in providing SOME protection contrary to what one reads on NOAA and many other web sites.
It does not help us solve the other question if rubber boots would decrease the risk of a direct strike. But if I was camping, sleeping in a tent and a lightning storm came up, before searching for the safest spot I could find, I'd take the time to put my boots on.

 

[davenn]

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.

I have stayed out of the discussion till now, but really the time has come to comment

Like Drakkith ... I also don't agree with this

We are talking about huge buildups of static charge in the cloud and below it on the ground
go back and remember your early physics lessons of experimenting with static charge
Insulated materials is pretty much totally irrelevant

you can build up large static charges on rubber balloons, glass rods ant non conductive material etc
Stop thinking about resistivity of a material and how it affects a DC current

you are treating lightning like a DC flow of current that needs a conductive material
this is a very false premise, concrete or wooden buildings that get struck are not electrically conductive
BUT that doesn't stop a huge static charge from building up on them that can result in a lightning strike

As a storm chaser I am well aware of build up of static charge
You can have 2 identically tall buildings ( or other objects) side by side, one gets struck the other doesn't
WHY?
because the area of charge build up is usually pretty confined, (I don't have links to papers on that
its from years of visual observations) the reason one building or other object tall or short gets struck is purely in the
location of the charge buildup. Once the buildup is high enough, leaders and streamers will form and the discharge will occur

You may get struck rather than the tree 50m away only because you were at the point where the max charge buildup was and for no other reason

Dave

 

[Drakkith]

It does not help us solve the other question if rubber boots would decrease the risk of a direct strike.

Which is what the discussion is actually about, so I fail to understand why you're so adamant about something that no one is even discussing . You're earlier post:

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.

You are claiming that the resistance of a person/car/other object has a direct and and obvious effect on whether or not lightning will strike it instead of another object. Please provide some quality references supporting this. (Youtube videos and popular magazine/blog articles are not quality references)

 

[FactChecker]

I found this.

from the National Outdoor Leadership School. if I was camping, sleeping in a tent and a lightning storm came up, before searching for the safest spot I could find, I'd take the time to put my boots on.

That's an excellent link. The potential across a short distance of ground is something I would not have thought of.

 

[DTM]

Dave, you are correct, I made a mistake there. The insulator will have little effect on the charge buildup since charge build up is a relatively slow process with lower current. However, given two equally charged and equally tall objects, let's say both directly below the center of charge in a cloud, the one with less resistance is more likely to initiate the streamers. The steamers carry a significant amount of current and they would be far more likely to originate from a path of lower resistance.

 

[davenn]

Hey DTM
have a think about this
another example ...

surely you have walked across a carpet in your rubber soled shoes/boots and felt the discharge zap to your hand/finger on the door knob etc?

your rubber soled shoes didn't do any good there against the 10 - 20,000 volts huh ? ;)
rather they were part of the cause of the buildup of static on your body

 

[davenn]

That's an excellent link. The potential across a short distance of ground is something I would not have thought of.

ohh yes, close to a strike, you could have 1000's of volts in potential difference between spread apart feet

 

[davenn]

lets say both directly below the center of charge in a cloud, the one with less resistance is more likely to initiate the streamers. The steamers carry a significant amount of current and they would be far more likely to originate from a path of lower resistance.

you are still not understanding/getting it

I will say it one more time
With a static charge and its buildup, materials electrically resistant to DC are IRRELEVENT to the flow of a current resulting from a static charge buildup

The streamers are NOT carrying current ... there is NO current flow till the discharge occurrs

 

[DTM]

Drakkith, I do realize this initial single topic has morphed into two for me. Likelihood of rubber preventing an object getting struck, and prevention of injury from a near strike. I think they are both important topics for discussion. I don't have a good source for an answer to either of these questions because I've looked a lot in the past and haven't found one. That's why I came to the physics forum for this discussion. I have an opinion based on my knowledge and experience with physics that is different from what's on the NOAA and other websites. I'm just trying to either convince others or have them convince me of the answers to these 2 questions.

 

[davenn]

car and EHT experiment

NOTE the discharge from the car wheel rim to ground
the 4 or so inches of rubber had no effect the discharge just jumped the gap
it had already just maybe several metres from the source to the top of the car

how do you think this would be any different for a lightning discharge to a vehicle or a person
where the lightning discharge has already traversed several kilometres of atmosphere ?Answer, no difference at all

Dave

 

[DTM]

Dave, Your carpet w/ rubber shoes examples is a great one. You may have convinced me... I get that static charge build up is irreverent (at least mostly I think) to resistance. I didn't realize that the streamers do not carry current. So if the streamers originate from the highest charged area, and they don't carry current, then I can see how resistance of the object would not effect a strike location. Good explanation.

 

[Drakkith]

I think they are both important topics for discussion.

Then you need to start a new thread for the other one if you want to discuss it, as it's making this thread very confusing and getting off topic.

I have an opinion based on my knowledge and experience with physics that is different from what's on the NOAA and other websites. I'm just trying to either convince others or have them convince me of the answers to these 2 questions.

That's all fine and dandy, but you need to be able to support your opinion with references.

 

[Drakkith]

The streamers are NOT carrying current ... there is NO current flow till the discharge occurrs

You sure about that? Wouldn't some current flow be required in order to transfer charges away from the area of charge buildup and keep the streamer propagating? The wiki article states it as about 50-100 amps, but I haven't been able to find a reference for that.

 

[davenn]

Hmmmm a fine line of definition maybe ;)
I was working on the principle that no current flows without a completed circuit
which doesn't happen till the leader/streamer from the ground meets the stepped leader from the cloud

I see where you are coming from and by definition it could be called a current
as a current is the flow of charge
( I'm sitting here and ummming and harring ;) )

I see it as an area of charge propagating out ...
how about an expanding electric field :)

I'm open to a clearer definition if one can be found :)

have a look at this classic pic, and this is for DTM as well

note the 2 streamers/leaders from the ground, one from the power pole yellow arrow)
and the one from the tree. Amazingly there must have been another leader from the tree that reached further and initiated the discharge

Dave

 

[DTM]

That's all fine and dandy, but you need to be able to support your opinion with references.

So if Einstein had wanted to discuss his theory of relativity on this forum, he shouldn't be able to because he'd have had no references ;) I know your response will be DTM is no Einstein...
I think all of this discussion is still relevant to the original topic which is basically, does an insulator effect an object being struck by lightning... I'm learning a lot from this discussion anyway.

Dave, The car getting struck by lightning does not disprove my point about relative resistance. You'd have to have 2 cars next to each other, one on rubber tires and one on steel rims and show they both get struck equally often...

So if a streamer does have some current, an insulator should affect that current and may affect which object 1st initiates that streamer.
I'm still uncertain. If it's true that an insulator has no effect on where lightning will strike, do you really expect a lightning rod to work as well if you attach it to a rubber boot sitting on the ground vs a metal rod driven into the ground?
However, I like Dave's example of static discharge from a carpet, which does seem to work just fine with rubber shoes... Too late to think about this anymore tonight.

 

[Drakkith]

So if Einstein had wanted to discuss his theory of relativity on this forum, he shouldn't be able to because he'd have had no references ;) I know your response will be DTM is no Einstein...

If this forum existed prior to Einstein's publications on relativity, no, he wouldn't be able to discuss them. Afterwards, yes, and he could simply "link" the peer reviewed papers as references.

So if a streamer does have some current, an insulator should affect that current and may affect which object 1st initiates that streamer.

Not necessarily. This isn't a wire and a resistor. An large insulator may have a much lower amount resistance than you'd think when it comes to high voltages just because of its size, similar to how increasing the cross sectional radius of a conductor decreases its resistance.

I'm still uncertain. If it's true that an insulator has no effect on where lightning will strike, do you really expect a lightning rod to work as well if you attach it to a rubber boot sitting on the ground vs a metal rod driven into the ground?

No, but lightning rods aren't built to simply attract the lightning, but to discharge it to ground without itself or the structure it's mounted on being destroyed in the process. This could be the main reason that lightning rods are connected to low impedance systems designed to transfer very high current to ground and may have little to nothing to do with the buildup of charge and the initiation of an upward streamer. And for the record I am not saying that the resistance of an object doesn't matter, I'm questioning your claim that it matters enough to greatly affect where a lightning strike will occur, especially in the context of two objects several dozen feet from each other.

 

[zoki85]

Few comments:

• In the case of an indirect strike it is certainly better to wear footwear with good insulating soles than standing barefoot. However, if step voltages are sufficiently high, footwear is useless: arcover will occur at voltages in order of few kV and the footwear insulation/resistance will be bypassed this way.
• I don't know of any studies/research conducted in HV labs showing difference in probability of direct strikes between set-ups with good grounding, bad grounding and thin piece of insulation put between base of the object and ground. IMHO, the difference should exist but is likely to be too small in megavolt experiments and objects of decent size.
• Streamers, or better long streamer-leader plasma structures, do carry significant impulse currents, have high peak dissipation power, and do change E-field configuration in space significantly (see my avat)
• Many things about lightning are still wrapped in mystery for modern science. Certain features of natural lightning discharge can be reproduced by UHV impulse generators in multimeter gaps; some others can not. Best what can be done is to study a rocket-initiated lightning during thunderstorm weather (there are few facilities in world than can do that). In such experiments an upward positive leader is generated. However, natural cloud to ground lightning is created by downward negative leader in aproximately 90% of the cases

 

[FactChecker]

I will say it one more time
With a static charge and its buildup, materials electrically resistant to DC are IRRELEVENT to the flow of a current resulting from a static charge buildup

The streamers are NOT carrying current ... there is NO current flow till the discharge occurrs

The question is not what happens after a static charge buildup. The question is whether you share the static charge buildup in the Earth that attracts lightning or causes streamers. Shoes can keep a static charge buildup in the Earth from traveling to you.

 

[zoki85]

Shoes can keep a static charge buildup in the Earth from traveling to you.

When downward leader at potential of aproximately -50 MV fast approaches to you, the charge buildup can be hardly called static.

 

[davenn]

Shoes can keep a static charge buildup in the Earth from traveling to you.

not likely ... for the reasons I have already stated ... reread the shoes on carpet then discharging on the door knob

 

[NascentOxygen]

Whenever there's a report of someone being struck by lightning, if there's one further detail I seem to learn it's that the person's shoes were blown off by the strike! It appears that shoes are no impediment to a lightning bolt---it deftly removes them!

What is amazing is that people survive a strike as often as they do, going on to gradually recover almost all affected faculties.

http://thumbnails109.imagebam.com/37332/0363e9373319108.jpg

 

[zoki85]

Person's shoes get frequently blown off in other HV incidents above 20 kV too. Unfortunatelly, people who survive, rarely recover completely.