When lightning hits water does the charge dissipate across the surface or go down into the water column? If I’m swimming in the ocean and lightning hits the water, how close would I have to be to feel the effects?
I think there are too many variables for a conclusive answer. The amount of eneregy in the bolt, the salinity of the water where you are (and the intervening distance from the strike), your physical state at the time, how much of your body is submerged, etc.
I was always told not to be in a body of water when there’s lightning in the area (meaning, I guess, “as far as I could see.”) You’re not even supposed to take a shower (or even a bath?) when there’s lightning around.
I like your question, though, about the dissipation. We know the discharge is to “ground” but what constitutes ground when in a body of water?
I was always under the impression that the current would spread out more or less uniformly in all directions, in other words like a hemisphere. That’s probably not exactly true since the water density isn’t uniform (it increases with the depth) but I imagine it is reasonably close.
Assuming this to be true, I once worked out roughly how far away you’d have to be from a lightning strike to be safe. I took a typical lightning bolt, which I figured would have maybe half a million amps of current, and calculated out two distances, one for where the current would be spread out to about 1,000 amps (roughly the same order of magnitude as what you get from the electric chair) and one where the current was spread out to 0.5 mA, which is the generally accepted “safe” level that U.S. safety standards are built around. In between those two distances, death is going to be more of a probability thing, with the probability decreasing with greater distance, of course.
The 1,000 amp distance worked out to be something like 10 feet, so if you are that close to the strike you are definitely going to be in a world of hurt.
The 5 mA distance worked out to be about 3/4ths of a mile.
For perspective, 1 mA is roughly where you start to feel tingling, 10 mA is about where your muscles start to contract involuntarily, and 100 mA is where the risk of putting your heart into fibrillation really starts to get severe.
Not sure this helps, but I can relate a story about lightning and water.
One day a few summers ago I was standing knee-deep and barefoot in a fresh water lake at a boat ramp. A sudden summer storm was developing, and we were trying to load our boat onto the trailer before the storm.
When I was cranking the winch, lightning hit out in the water, I would estimate about 30 yards or so from where I was. For a split second I thought someone else had backed their boat trailer into my legs (because it was a multilane boat ramp), my knees buckled / muscles contracted and I fell over backwards into the water. I quickly realized there was no one else on the ramp. I had felt the lightning.
After it was over, there were no lasting effects. I had no pain or anything else. I had only felt the shock while the lightning was ocurring.
So some random guy (me) estimating lightning at a distance of 30 yards (but hell, it coulda been 100yds, who knows really?), I can tell you its enough to knock you on your ass.
the caution for scuba divers is to go as deep as possible and stay there for the storm length or as long as you can, unless you have a boat with cabin which is somewhat safe or can get to shore and shelter quickly.
Not directly on point, but some public indoor swimming pools will ban swimmers during a thunderstorm, but others don’t. Once I asked the lifeguard why the pool was not evacuated, and she said the pool is grounded. That may be, but the charge can be conducted by pipes and other metal objects.
metallic plumbing and any water connected to it can be a path for electricity on its way to the earth, it will go all directions before it reaches the earth.
So are people struck by lighting. :smack:
When I was working for a house mover we had a little seminar on electrical safety. One of the guys who was there was a house mover who was holding a power line in both hands (while ungrounded) and inadvertantly allowed a grounded cable to touch the back of his neck. He could open beers with those hooks and everything, but he made an impact on us.
Anyway, the power company guy said when you’re escaping a downed power line think of a bullseye. The highest potential (voltage) is at the center, where the wire is. As you travel away from the wire, the potential drops. It’s the potential difference that kills. Imagine you’ve got both feet at 6,000 volts. No problem, but take a big step and you’ve got one foot at 6,000 volts and one at 5,000 volts. There will be a current flow from the higher to the lower potential.
Of course, it won’t be a perfect circle, soil conditions and moisture will affect the shape, but in general think of a bullseye.
He said never put one foot ahead of the other. Take baby steps such that your leading heel is never farther away from the current source than the toes on the trailing foot.
People asked if a jump was quicker. He did not recommend it, because a full length fall puts you at all kinds of risk.
I’d imagine the same thing applies in water. If your treading water when lightning strikes, your head up at the surface will be at a different potential than your feet 5 and a half feet down. How great the difference is will depend on factors like salinity and distance from the strike.
I thank engineer_comp_geek for his calculations. However, keep in mind these other things. Lightning has come for miles in the open air to get to the water, and it has no respect for logic and math once it touches down. It sometimes sends out little sprigs of itself for quite a distance around the main strike.
Folks along Florida’s gulf coast are warned that lightning sometimes strikes miles ahead of the forward edge of that anvil-shaped cloud. You might also be the luckless pedestrian who gets the first lightning bolt out of a new storm.
In the brief span of my 61 years, scientists have changed the accepted wisdom several times about up vs. down strikes and which end is positive. Today’s answers are up and down, positive and negative, and sometimes it changes within one strike. Wise people told us that “heat lightning” that doesn’t strike the ground did not exist. That was just distant lightning, they said. We now know that intra-cloud lightning happens all the time. Layers of the same storm may be positive, negative, and positive again, and lightning passes up and down between the layers.
This post, I realize, does not directly answer the OP, and I apologize for that.:smack:
Just as an aside to redo the real-world calculations, I’ve google-checked that lightning bolts max out at ca. 100,000 Amp.
Not directly, but pipes leading into the pool can conduct electricity, and the pool water is a conductor also.
These guys say it can get up to 300,000 amps a 1 billion volts
Well, everybody knows that the amperage spikes for positive lightening (I didn’t…).
Who you gonna believe, me or The National Oceanic and Atmospheric Division?
In college, I was building a weather station for a remote location which was periodically struck by lighting. Started reading up on the subject, and applied the information on other jobs. Talked to people who worked in the field has been eye opening. Probably the worse story I heard was the guy who set up AM radio towers in Colorado in the 50’s. He was waiting out a storm in his truck and watched a horse explode when lightning struck it. Yeah, it blew out its internal organs. Another time he watch cowboys rounding up a heard of cattle when a bolt out of the blue hit and watched 200 cattle, three horses, and three cowboys jump in the air about a foot simultaneously.
It is absolutely irresponsible for anyone to be outdoors in a swimming pool during a lightning storm. Any government or agency that allows swimming to go on during an electrical storm will be (not *could *be) sued for negligence if someone is killed or injured as a result of a lightning strike in or near the pool. Now imagine 50 people die in the pool because of an errant strike.
This is a no-brainer for a personal injury lawyer (and BTW that lifeguard will be named as a defendant–imagine the wonderment she feel when she’s asked on the stand, “Why did you allow this to happen?”).
You can read up on some the issues with this PDF. Note: swimming pools are not mentioned in the document (which is about nine years old), but the move has been towards increasing responsibility for the parties who manage public and private facilities and less about “an Act of God”.