Lightning strike proximity?

[omega1]

Hi,

I was just watching the news in rochester and it seems someone else got hit with lightning and was brought to the hospital but survived...

so my question is,

Since the lightning is traveling upwards of 2 miles to reach you from the clouds, does it cut down a lot on its lethality?

Suppose the same bolt hit you and the cloud was only 20 feet in the air, would it make much difference assuming all else is equal?

[GrandMasterTerwynn]

Hi,

I was just watching the news in rochester and it seems someone else got hit with lightning and was brought to the hospital but survived...

so my question is,

Since the lightning is traveling upwards of 2 miles to reach you from the clouds, does it cut down a lot on its lethality?

Suppose the same bolt hit you and the cloud was only 20 feet in the air, would it make much difference assuming all else is equal?

No. People have been killed by lightning strikes originating from thunderstorms well over ten to twenty-five miles distant. And, on the other end, pretty much any electrical discharge strong enough to cut a conductive channel through even a few feet of open air (which is a very good insulator) is strong enough that it easily has the potential to kill you.

[Simon_Jester]

The bolt doesn't really disperse with distance the way, say, a flashlight beam would. For lightning to travel through the air at all, it has to generate a path of ionized air. The current can travel through the ionized air, but can't travel through the non-ionized air around it. Which means that, in effect, the path of a lightning bolt is more than a little like a very long insulated wire- and insulated wires are very good at carrying concentrated electrical energy from one place to another without losing it.

If the clouds were very close to the ground, you might well see less dangerous lightning, because it would be easier for static charges in the clouds to make their way to the ground. You might expect to see many relatively small sparks, instead of infrequent, high-intensity bolts.

[Dooey Jo]

It's worth pointing out that even if lightning did work that way, for the majority of strikes, the current travels from the ground to the air. See here (the little ones coming out of the clouds are opening up ionization channels in the air which allows charge to flow when one of them eventually hits the ground).

But if the clouds did travel closer to the ground, the voltage needed for a discharge would be a lot smaller, so you would see more but less intense sparks. However, if the cloud was only 20 feet up, I suppose it's possible the charges couldn't build up in the first place.

[Sea Skimmer]

The distance should cut down on lethality. But then a 10 megaton nuclear bomb is also more lethal then a 1 kiloton nuclear bomb; it doesn’t make a lot of difference if it hits you. The real difference comes from what path the lighting takes traveling across your body. The people who survive being struck by lighting mostly do so because the current primarily traveled across the surface of the skin. It’s when a major portion of the current travels through your interior organs and blood stream that you are either cooked to death or have heart and brain functions fundamentally disrupted. I can't really explain how helicopter linesmen repair works, but IIRC its based on making the voltage flow across your skin by giving you a massive neutral charge. Then even a million volts are not a threat.

I believe in ‘normal’ range of atmospheric conditions you need about 500- 1000 volts to visibly spark across a 1cm gap of open air. Meanwhile anything over 80 volts is a serious hazard to a human and even 9 volts can kill in the right situation. IIRC though 1.5 volts right into the blood steam can be enough to stop the heart. So the voltages lighting needs just to exist are always going to be very dangerous.

[Seggybop]

Voltage by itself won't actually hurt you; you need adequate current to cause damage. There is a minimum threshold of voltage required before a human can be injured simply because humans under normal conditions aren't conductive enough. That's why it's almost impossible to hurt yourself with common batteries, even though they're often capable of delivering substantial current. If the voltage is too low, the human won't conduct, or won't take serious damage because the resistance is too high for the electricity to take a path through their heart/other critical organs.

[Isolder74]

Let me put it this way. The 1/2 inch gap jumped to make a Jacob's Ladder work requires enough current to usually kill you. Any case of a person getting hit by lightning and surviving is usually going to be just a case of being very, very lucky and having the current take a route through the body that doesn't case it to kill outright giving them a chance to save you.

[starslayer]

I can't really explain how helicopter linesmen repair works, but IIRC its based on making the voltage flow across your skin by giving you a massive neutral charge. Then even a million volts are not a threat.

IIRC, helicopter linesman repair involves getting within a few meters of the high voltage line, but no closer than that; then there isn't enough voltage to break down the intervening air. The cleaning fluid is extremely pure water, shot out of a very high pressure hose; if there's even a tiny amount of impurities in the water, it will conduct well enough to pretty much vaporize the helicopter's occupants and utterly destroy the helicopter.

There is no such thing as "neutral charge" - charge is either positive or negative, and near the massive electric field of a high voltage transmission line, you will develop an induced charge no matter what you do.

[Sea Skimmer]

I don't know what you are talking about with water; I'm talking about replacing the spreaders that hold the wires in place and that involves helicopter-wire contact with an actual cable they clip onto the wire. They do something to the charge of the chopper to control the arcing when they do so otherwise it would indeed b exploded out of the air but I once more don't have the time to spare to look that up; when I get back from school I shall. A neutral charge is when you have equal positive and negative charges.

[Pu-239]

Um, that sounds a bit off. It works because the helicopter, linesman, and line is all at the same electrical potential (> 1000VAC). Clipping the wires is so the linesman doesn't get electrocuted due to the helicopter being at some other potential (it's floating but probably close to ground, designated as 0V?) resulting from current flowing from the line to the helicopter - IIRC clipping the helicopter equalizes the voltages so that no current flow occurs beyond the initial jolt causing some arcing. If the helicopter happened to touch the ground or the other transmission line that would cause a voltage difference between the line and the helicopter/linesman, causing bad things.

[Sea Skimmer]

Um, that sounds a bit off. It works because the helicopter, linesman, and line is all at the same electrical potential (> 1000VAC).

Well what I read was if they just clipped on normally the initial arc would be large enough to be a explosion resulting in bad things in terms of crash avoidance; so the helicopters are rigged to generate an initial neutral charge of something like 65,000 volts to reduce the difference. Then they can equalize. Maybe that was just wrong, electricity is not something I know well.

[Simon_Jester]

I think what's going on there is that the helicopter wires a high-voltage power source to its own frame to generate a voltage equal to whatever they'd get off the power line- which places them at high voltage relative to the ground, but zero voltage relative to the line.

At least, that's what I infer from knowing basic physics and a little HV engineering, but only a little.

[omega1]

Great replies guys,

So I suppose the scene in the movie Sorceres Apprentice when the star of the movie has electricity arcing at him for 10 minutes from these massive machines is a bit far off? Wouldn't a constant stream of that nature and power obliterate you even if you were grounded? Doesn't 'grounding' have limits under duration of bombardment by lightning?

Anyone know the scene I speak of?

[starslayer]

I don't know what you are talking about with water; I'm talking about replacing the spreaders that hold the wires in place and that involves helicopter-wire contact with an actual cable they clip onto the wire. They do something to the charge of the chopper to control the arcing when they do so otherwise it would indeed b exploded out of the air but I once more don't have the time to spare to look that up; when I get back from school I shall. A neutral charge is when you have equal positive and negative charges.

Sorry; I misread "repair" as "maintenance" somehow.

Great replies guys,

So I suppose the scene in the movie Sorceres Apprentice when the star of the movie has electricity arcing at him for 10 minutes from these massive machines is a bit far off? Wouldn't a constant stream of that nature and power obliterate you even if you were grounded? Doesn't 'grounding' have limits under duration of bombardment by lightning?

Anyone know the scene I speak of?

Yeah, a bit. Even if the current is so small that it wouldn't kill him outright, giant arcs still consume a lot of power and generate a lot of heat. Were he a real person, he would be severely burned at best, but yeah magic.

Being grounded just means that there is an electrical path to ground through you. When being threatened with lightning, etc., being grounded is actually a bad thing, because it means the lightning will flow through you preferentially. Bad news for you. You want something else in your general vicinity to be a better ground than you are, hence lightning rods. In the case of a car being one of the safest places to be during a thunderstorm, this is true, but for a different reason. A car is what's called a Faraday cage, basically a metal box. Because the electric field inside a conductor is always zero (in the static case, anyway), the current flows around the outside of the car and into the ground, entirely bypassing you.