I experienced a lightning strike about 50 yds away. I happened to have my hand on a metal edge to a table and got knocked off my feet, while the other ungrounded folks just got impressed by the flash and the boom.
Diving and lightning
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The salt and fresh water stuff is right on the money. But the bird on a wire is a little off. Being a barehand certified lineman (not PADI 
) that is a very important law of electricity to me. Electricity has to have a path to go anywhere. When a bird lands on a wire he becomes energized at the voltage of the wire. As long as he touches the wire only he is fine. A bird recieves a tiny sensation similar to the one we get when we stagger up to the juke box and get a little static shock. But there is no real danger. My crew works 230,000 volts hot using the same method. We get a little shock when we hook on to the line but it is just an annoyance. We can touch tools in the bucket, each other whatever as long as it is at the same potential as we are. Wow, that sure went a long way! What the h... does this have to do with diving?
Joe
) that is a very important law of electricity to me. Electricity has to have a path to go anywhere. When a bird lands on a wire he becomes energized at the voltage of the wire. As long as he touches the wire only he is fine. A bird recieves a tiny sensation similar to the one we get when we stagger up to the juke box and get a little static shock. But there is no real danger. My crew works 230,000 volts hot using the same method. We get a little shock when we hook on to the line but it is just an annoyance. We can touch tools in the bucket, each other whatever as long as it is at the same potential as we are. Wow, that sure went a long way! What the h... does this have to do with diving?Joe
You missed the point....
The reason the bird does not get electrocuted is that the potential between his two feet is almost exactly zero (that is, the wire has near-zero resistance, therefore the EMF between the two points is nearly zero, and no current flows through the bird's legs)
If the "wire" had considerable resistance over a short distance for some reason, then the bird would become the conductor - and ZAAAAAP!
You in the bucket truck typically only touch the wire at one point. But if you touched it at two points, then the same thing would apply - as long as the bare wire has near-zero resistance (nothing has an actual zero resistance - superconductors get exceedingly close, but "zero" ohms is essentially unobtainable) you're just fine.
Let's assume that between the two points there is 0.0001 ohm of resistance. Let's further assume the line carries 20,000 volts @ 5,000 amps, or 100 kw.
Across that 0.0001 ohm of resistance, at that current draw, there is one half volt of EMF. This is well under that necessary to breach your skin's resistance, and nothing bad happens. (E = IR) Even if you artificially lowered your skin's resistance (say, by soaking you hands in salt water) you'd probably be ok, because your resistance would be so high relative to that of the wire that the share of the current passing through your fingers would be unlikely to do anything other than give you a slight tingle.
But let's say there is 1 ohm between the points where your two hands touched the wire. Now there is 5,000 volts across those two points, and you're fried hamburger! (E = IR again) Assuming the resistance of your body is 4.999 kohms; there is 5,000 amps of current flowing, the total resistance is 5 kohms, and while the wire gets most of the current you get 1 amp of it - the amount necessary to stop your heart is well under that.
The point I was attempting to make is that its the EMF differential between any two points in your body that have the field impressed upon them that matters. If the differential exceeds that required to breach your body's internal resistance, AND if your internal resistance is low enough for a significant part of the current to flow through you (rather than through the other medium), you're toast.
The reason salt water is less dangerous is because its LOWER resistance means that the field dissipates more quickly, and thus remains dangerous for a much smaller radius from the point where the energy enters the water.
if there was that much resistance in the wire over a short distance it would burn down long before the bird could land on it. and if I missed the point I'd have been dead years ago.
better check your math too. 20,000 volts @ 5,000 amps is just a wee bit more then 100 kw
RichLockyer
Guest
Hehe... megawatts =-)
2deep4u
Registered
Hi all,
I have done almost all of my diving in guam where lighting is a rarity. In my DM/AI trainin we never metioned anything about lighting. I have done a few dives in Guam during some storms but was told that once your underwater you are safe because the water scatters the lightings energy to where it wont hurt you. Is this true or where they blowing smoke up my butt. thank you.
I have done almost all of my diving in guam where lighting is a rarity. In my DM/AI trainin we never metioned anything about lighting. I have done a few dives in Guam during some storms but was told that once your underwater you are safe because the water scatters the lightings energy to where it wont hurt you. Is this true or where they blowing smoke up my butt. thank you.
Are you talking about salt or fresh water?
The location in the world is also important. Here in Florida in freshwater lightning energy can travel a long way in a very unpredictable manner.
In salt water the energy is dissapated very quickly.
For a diver the greatest risk is when entering or exiting the water.
The location in the world is also important. Here in Florida in freshwater lightning energy can travel a long way in a very unpredictable manner.
In salt water the energy is dissapated very quickly.
For a diver the greatest risk is when entering or exiting the water.
Here's a link to a recent thread about a divers experience with lightning in Sydney.
http://www.diveoz.com.au/discussion_forums/topic.asp?TOPIC_ID=4855
http://www.diveoz.com.au/discussion_forums/topic.asp?TOPIC_ID=4855
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