Lightning hitting the sea question?

Question

If I was in the sea, swimming, and lightning struck the sea a few miles away, would the water conduct the electricity and kill everything in the ocean, including me? How close would the strike have to be in order to be a threat to me? Does salt water or fresh water make a difference?

Answer 1

At the risk of appearing lazy...this answer is a modification of an answer I gave to a similar question. It boils down to the voltage drop across your body as a function of distance from the point of contact...

In both fresh water and sea water, you're certaily safe at a distance of a few miles. But there are serious differences at closer range.

Assume peak current of 30,000 amps and that the charge spreads out uniformly in all directions - as an expanding hemisphere.

Current density will be 30,000/(2*pi*r^2)....we'll round that to 4800/radius^2 in meters. (amps/meter^2)

At 100 meters that implies a current density of about .48amps/m^2.

Assuming a conductance of 5mho/meter...that works out to a voltage drop of 0.096 volts per meter.

You're safe a football field away. Even at 30 feet the electric field will only be about 10 volts per meter.

Fresh water...completely different story...the lower conductivity of fresh water (by a factor of 1000 or more) means the electric field will be much higher at any given distance...at 100 meters you could easily be subjected to a difference of 100 volts across your body - depending on its orientation. At ten meters...about10,000 volts. Even at the longer distance you're probably still in danger in fresh water.

Someone....PLEASE CHECK MY MATH!

In answering a previous question of this nature concerning sea water, I did conclude correctly that one is definitely safe at 100m...but I hurried and got the numbers flat wrong.

Answer 2

(answer taken verbatim from the source - typos and all!)

The sea is not like your bath tub, as the sea is much much larger than even a very big bathtub.

After all, there is lightning hitting some part of the oceans some place, some where, every minute of every day, isn't there?

If it were just like dropping a radio into a bath tub, then people playing in the ocean at Virginia Beach would be shocked to death whenever lightning struck the water off the coast of South Africa.

But we know that doesn't happen.

Water has resistance. Salt water has a lower resistance than drinking water, but it does have some resistance. That resistance is cumulative per unit of volume of water.

As the distance grows from the strike point to the observer, the amount of energy observable is less.

More input:

* Resistance is not the major determiation wether the one feels it, it is dependant on the voltage and current in that strike (changed by how far electricity has to travel, humidity, size of clouds, etc.). To see why, look at how lightning works: friction, among other things, releases negative electrons in the sky. In a storm this charge of electrons that have no place to go become attracted to the positive charged earth and take that leap. They hit the water and spread. Everything that has room takes an electron (ionizes) and the charge disipates. My speculation is that after 100 feet or so you probably wouldn't feel it too much. Is someone going to jump in the water during a storm? It isn't recomended.

* Salt water is actually a very poor conductor of electricity. You should be pretty safe at sea.

* Salt water is a much better conductor than fresh. Salt water contains positive and negative ions (Na+ and Cl-), which lower its resistance. Fresh water, which contains fewer ions to transport charge, will have a higher resistance. Thinking about it a little longer: V=IR, where V = voltage, I = current, and R = resistance. In the case of a lightening bolt, I would imagine you could consider it a two resistor system, the water between you and the strike being the first resistor, and you being the second. Voltage will be supplied by the lightening bolt. The voltage will drop after travelling through the water. If there is enough voltage to provide a large enough current through yourself then you will feel it.

* What a person will feel (1ma)/ will kill them (10ma) is not directly based on distance from the strike, it is based on the voltage gradient (across the person), which is determined by the distance from the strike and the other paths that the charge can take to the earth. So, it is not linear or easily calculated because of the many different variables.

* 1st: Pure water is an insulator. Salt and impurities make it conduct. 2nd: You cannot separate voltage, current and resistance. They are related to each other. The voltage of the lightening strike, along with the resistance of the water determines the current allowed to flow. Current is limited by resistance. Current can be increased by increasing voltage or decreasing resistance. Therefore, the distance from the strike will increase resistance and therefore decrease current; voltage will drop as well (as in a voltage divider circuit). There are several laws that I can think of, (multiples of resistance, etc) that would probably help answer the question, but it's just not that simple. It's not even known why lightening "chooses" the path it takes in the first place. Bottom line, if you can see lightening, get out of the water.

Answer 3

Water is actually a very poor conductor. You usually have to add a catalyst to the water so that it can conduct electricity better. Fish and other wildlife do get killed by lightning striking lakes and oceans but only for very short (10 to 50 feet) distances.

Answer 4

Since the sea is filled with elements other than water the electricity disperses relatively quickly,so a few miles away you would be o.k.If the bolt struck within a hundred feet or so,you and the surrounding animals you have a strong probability of getting electrocuted.Fresh water acts as a better conductor for electrons to flow through,other than the sea water that is filled with elements other than h2o...tom science

Answer 5

I've asked this question many many many times to science teachers and the best answer I have ever gotten was: No, you would not be electrocuted, because of the MASS of the ocean can absorb the energy of the lightning bolt.

I think salt water is more conductive, but still the same answer.

PS, don't swim when it's storming.

Answer 6

i live in the lightning capital of the world and have seen a lot of strikes in the ocean. but salt water is a bad conductor of electricity. i think only a tiny radius of the strike would be deadly.

Answer 7

Check out this article. It depends a lot on the type of lightning, the closeness of the strike, and some other variables. Very interesting quesetion.