Lightning and Diving

[Firebrand]

Fortunately I rarely face that living here in soCal, but I grew up and started my diving in the Midwest. I never dive with lightning striking within visual distance. I'm a wimp... two lightning bolts, separated by several years, struck within feet of my bedroom. I don't want a third strike!!

Dude, you're just bad luck when it comes to lightning!

 

[serambin]

Dude, you're just bad luck when it comes to lightning!

I don't know about that, so far he's dodged the bullets.

Stan

 

[knotical]

Interesting and important topic. Here are a few other relevant threads from various SB forums. Some posts have pointers to other websites with additional information and recommendations.

http://www.scubaboard.com/showthread.php?t=86982

http://www.scubaboard.com/showthread.php?t=68018

http://www.scubaboard.com/showthread.php?t=2150

 

[lamont]

Lightening doesn't penetrate water, it DOES skip across it though, so if your surfaced you can get hit, under and your fine.

Somewhere around here there's a report a few years back of cave divers getting hit by lightning in the cave, so it definitely can both go through ground, through water and through divers in the right conditions.

 

[roakey]

search->advanced search, keyword "lightning" and restrict the search to titles only.

There's an existing reply with over 100 replies, I don't see how anyone's going to offer anything new here.

The search function is your friend.

Roak

 

[miketsp]

Lightening doesn't penetrate water, it DOES skip across it though, so if your surfaced you can get hit, under and your fine.

Sorry, this is simply not true for sea water.
The current will follow the path of least resistance.
Salt water is a homogeneous conducting mass so the current will spread out in all directions into the hemisphere.
Fortunately the intensity you will feel will drop off as the square of the distance from the strike so you don't have to be that deep to be safe.
How deep has been discussed on other threads.

As for fresh water, it really depends how pure it is.
Distilled water is actually quite a good insulator but most cave water is pretty loaded with salts and other impurities, which when wet conduct well.

 

[captain]

Thing about electricity is that it doesn't really affect if you at at the same voltage potential. If you are submerged in the water and lighting hits the water, the water and you become charged to the same voltage. If there is no difference in potential, electrical flow or ampage can not pass through the body. It is the flow of electricity that does the damage. Have you ever seen men working on a high voltage line from a helicopter. The line is energized with up to 230,000 volts but it doesn't harm them because the worker and helicopter are all energized at the same potential, 230,000 volts. It does cause a tingling and itching sensation from the ionized air around the line sort of like the way static electricity makes your hair stand on end.

 

[Tom Smedley]

I agree - when you are in the water and not touching anything there is a lack of potential difference.

I was diving once with a guy who saw the flashes and got scared. He came up the wrong anchor line and was hanging on the ladder of someone else's boat. They were hesitant to let him on board and were trying to talk him into swimming to the correct boat. The boat has a galvanic ground so as long as he held the ladder the potential difference existed. Everytime that lightening flashed in the distance he would holler. I finally talked him into letting go of the boat and all was well. He didn't waste any time getting on the correct boat.

As with Vortex Spring or on a boat, You are infinately safer under the water than you are under a tree or on the metal deck of a boat.

 

[miketsp]

I agree - when you are in the water and not touching anything there is a lack of potential difference.
..snip..
As with Vortex Spring or on a boat, You are infinately safer under the water than you are under a tree or on the metal deck of a boat.

The first part is not correct, the second part is OK.

Water has a finite resistance and a very high voltage strike at a point on the surface will cause an electric field gradient radiating out in all directions into the hemisphere due to current flow. Each cubic inch of water has resistance and current flowing through it radially from the strike. This causes a voltage drop. Depending on the orientation of your body in the water your body will act as a parallel conductor and there will be some current flow.
Fortunately this effect falls off rapidly with distance.

In the case previously cited of high tension powerline workers the gradient in the air around their bodies is minimal and so their whole body is at practically the same potential.


Just for the record there is a nice summary of boating protection at
http://www.cdc.gov/nasd/docs/d000001-d000100/d000007/d000007.html

 

[Tom Smedley]

Possibly true but it doesn't explain that when there is lightening and you are immersed you don't feel the electric tingle. However, when you are touching an object such as a boat you definitely feel an electrical shock. When your body is immersed and not touching a ground to complete a circuit it is the same as a bird sitting on an electric wire.