Lightning question
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The answer to this question is very complicated and I can give only a partial answer. The first thing one should know about lightning is that it does not behave in predictable ways. I have had mountain top weather stations completely destroyed by a hit, others survived with only burn marks and others had one single component fried...and this is with full lightning protection installed.
The commonly held belief that electricity finds the path of least resistance to ground is false....it finds ALL paths...some to a lesser degree than others. So this means that even if you are inside the cagelike body of a metallic boat or automobile you can still be killed if you happen to have a well conductive (read wet) hand resting on the metal of the vessel and another part resting on another metal part. If you are making good enough contact you will get some current passing through you. And it only takes a few milliamps passing through your heart to stop it.
My thoughts are that if you are at the surface during a T-storm you may be at risk due to the convenient path to the electricity you are exposing. Getting rid of the rig at the surface may be the best approach so that all you are wearing is insulating rubber. Then I would not touch the boat until I saw a strike from the cloud above strike elsewhere. This would give you a little bit of time to get on the boat before the cloud rebuilt its potential. It would certainly ruin your day if you grabbed the boat at the same time it was hit.
When underwater I believe one is relatively safe...certainly better than being on the surface. Salt water is a great conductor so would dissipate charge somewhat like the earth does and you would have to be extremely close to the hit to provide enough differential across your body to allow current to flow.
But again, lightning is so unpredictable in its behaviour. The best prevention is avoidance. Include weather changes into your dive plan.
The commonly held belief that electricity finds the path of least resistance to ground is false....it finds ALL paths...some to a lesser degree than others. So this means that even if you are inside the cagelike body of a metallic boat or automobile you can still be killed if you happen to have a well conductive (read wet) hand resting on the metal of the vessel and another part resting on another metal part. If you are making good enough contact you will get some current passing through you. And it only takes a few milliamps passing through your heart to stop it.
My thoughts are that if you are at the surface during a T-storm you may be at risk due to the convenient path to the electricity you are exposing. Getting rid of the rig at the surface may be the best approach so that all you are wearing is insulating rubber. Then I would not touch the boat until I saw a strike from the cloud above strike elsewhere. This would give you a little bit of time to get on the boat before the cloud rebuilt its potential. It would certainly ruin your day if you grabbed the boat at the same time it was hit.
When underwater I believe one is relatively safe...certainly better than being on the surface. Salt water is a great conductor so would dissipate charge somewhat like the earth does and you would have to be extremely close to the hit to provide enough differential across your body to allow current to flow.
But again, lightning is so unpredictable in its behaviour. The best prevention is avoidance. Include weather changes into your dive plan.
This is an opinion on the subject, with some scientific fact:
Lightning and Diving
I have been in seawater less than 30 FT deep with multiple lightning strikes to a partially submerged rock jetty less than 20 YDS away. Loud as hell when I surfaced to see what all the flashes were then immediately headed back to the bottom. Not even a twitch.
Similarly, as a paramedic, I defibrillated a patient at 360J while standing in ankle deep water next to the patient. The patient had a cardiac arrest in the middle of a thunderstorm and was lying in a parking lot. For you PM types out there, it was a LP 5 with paddles on bare wet skin and a LOT of pressure. Again, not even a twitch.
See this thread.
Remember, electricity can be your friend!
Lightning and Diving
I have been in seawater less than 30 FT deep with multiple lightning strikes to a partially submerged rock jetty less than 20 YDS away. Loud as hell when I surfaced to see what all the flashes were then immediately headed back to the bottom. Not even a twitch.
Similarly, as a paramedic, I defibrillated a patient at 360J while standing in ankle deep water next to the patient. The patient had a cardiac arrest in the middle of a thunderstorm and was lying in a parking lot. For you PM types out there, it was a LP 5 with paddles on bare wet skin and a LOT of pressure. Again, not even a twitch.
See this thread.
Remember, electricity can be your friend!
SkipperJohn
Contributor
Most larger boats are fitted with something called a lightning arrestor. It is basically a grounding plate of modest size that, due to it's irregular surface, has a surface area of something several times the bottom of the boat. This coupled with a good grounding system enables a boat to be struck by lightning and have the current routed safely to the water below. The system is not fool proof but it's the best we have. There are a few things you could do to minimize your chances of sustaining injury should a vessel you are on get struck. Dont become the path of least resistance. The lightning is looking for ground (or in some cases going the other way). Try not to hold onto any metal. On most boats, if you want to hold on at all this is next to impossible. I would advocate wearing your boots while on board and gloves if you have them. I was running a boat once without any lightning arrestor and a nearby wave was struck (because the wave was higher then the boat!) I was wearing regular cloth gloves and felt only a small shock. All my electronics blew but that's another story.
By the way, usually before a strike there are telltale signs. We felt and even smelt the charge before the strike. We had some fishing rods on board and a few seconds before sparks began to jump form the tips to one another. If you are dry you may feel your hair beginning to stand on end. This is not always the case, but if you are out in a storm and witness any of this I would get low and insulated.
On another point, if you are in a thunder squal on a boat, I would be more worried about the wind than the lightning. Lightning strikes are rare. Boats being battered by 20 foot waves in 70 MPH winds are not. Should you get caught in a storm DO NOT go into the cabin. Doors have a habit of slamming shut and being held shut due to water pressure. Take off your weights (I know this seems obvious but on a recent trip with severe thunder storms all around us one of our divers refused to remove his weight belt). If you have a wet suit, wear it. Know where the lfe jackets are & follow the directions of the captain and crew.
By the way, usually before a strike there are telltale signs. We felt and even smelt the charge before the strike. We had some fishing rods on board and a few seconds before sparks began to jump form the tips to one another. If you are dry you may feel your hair beginning to stand on end. This is not always the case, but if you are out in a storm and witness any of this I would get low and insulated.
On another point, if you are in a thunder squal on a boat, I would be more worried about the wind than the lightning. Lightning strikes are rare. Boats being battered by 20 foot waves in 70 MPH winds are not. Should you get caught in a storm DO NOT go into the cabin. Doors have a habit of slamming shut and being held shut due to water pressure. Take off your weights (I know this seems obvious but on a recent trip with severe thunder storms all around us one of our divers refused to remove his weight belt). If you have a wet suit, wear it. Know where the lfe jackets are & follow the directions of the captain and crew.
firefly_843
Registered
Just to add some information. Lightning can be positive or negative in polarity. Positive bolts originate in the top of a cloud and are much more powerful than negative bolts. This explains why sometime there is massive damage and other times not. "Bolts from the blue" are positive and the channel can be 20 miles long, and of coarse there are also more deadly to humans. Now, when lightning strikes water the current has be shown to spread across the surface and ony penetrate a couple of inches so submerging is probably your best bet.
Crush
Contributor
I see no reason why that should be the case and I doubt that, in general, that notion is correct. bygolly's explanation of lightning taking all paths is correct - mine was a simplification. However, to a very good approximation in the real world lightning does take the path of least resistance since the resistivities of objects around us tend to be quite disparate from our own, making us either the path of choice or not.
firefly_843
Registered
Well, I have a link, but I've got to get to 5 posts.
firefly_843
Registered
Ok, one more time.
firefly_843
Registered
Sorry Guys, had to get my 5 posts. Here is the link to the study:
http://www.lightningsafety.com/nlsi_lhm/Radials.pdf
http://www.lightningsafety.com/nlsi_lhm/Radials.pdf
Crush
Contributor
No joy with your link.
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