My Stupid *** Question...

[miketsp]

..snip..
My question is... What would lightning do to a diver under water or waiting to board a boat and are you safe from it's effects at a certain depth?

I've wondered about this but have not asked as to not sound like an idiot.

Thanks for any info! Marc

It's not a stupid question. Many people have difficulty visualising concepts like 3 dimensional voltage gradient vectors in a homogeneous medium or what causes skin effect when a high frequency pulse tries to propagate in a conductor.

I won't speculate, I'll just have you read this.

Just a couple of comments on the article.

"It's not clear how far lightning travels through water."
The calculation is not that difficult, the problem is to parameterize the strike as they vary significantly. If you know the current and the pulse shape, the result can be calculated.
Especially for sea water which is a homogeneous conducting medium.
There are some statistics available on the Internet. In a previous thread on the subject I calculated the voltage gradient across a 2m tall diver to establish a safe depth for various currents.

It was post #22 of
http://www.scubaboard.com/showthread.php?t=113662

However as was pointed out later, this calculation was based on a slow pulse which would have better penetration.
I did run some later simulations using some typical pulse shapes and must admit that skin effect does come into play to a large extent for the majority of strikes so the depths I published really are worst case and the dissipation will normally confine itself to more shallow depths.

See also thread
http://www.scubaboard.com/showthread.php?t=133014

 

[Dive-aholic]

I investigate boat related deaths. I am also certified through the Underwriters Labratory as an advanced boating accident investigator. My department investigates such electrocutions. Actually marina related electrocutions are very common. Many "unexplained drownings" are a result of stray AC current. There are protocols divers must follow when diving marinas, such as locking out circuit panel boxes, testing the water with a multi-tester, etc. Diving marinas should be considered extremely dangerous. Many sources of stray AC current often enter the water through the metallic outdrives of vessels or poor wiring. AC current coming from a boats lower unit travel in a cone shaped pattern toward the bottom. A diver entering this cone will become paralyzed and usually risks a severe chance of dying. If you want to clean a boat hull, don't do it at a marina if you are planning on living a little longer. Get away from anywhere there is shore power and disconnect any generators, battery chargers, invertors,etc. Most people are unaware of this danger. Swimmers entering current die but their deaths are often attributed to drowning, not electrocutions.

That makes sense and is kind of what I was alluding to. The electrocutions that occur in marinas is due to manmade current, not lightning strikes.. The AC is going to be more directed than a lightening strike. Diving in that cone would be harmful, but diving next to wouldn't, as long as you don't stray into it. BTW, I don't dive in marinas.