Lightning

[Toiyabe]

Which is it? Do the other structures supply protection from lightning coming down between buildings and hitting one in the sides. What is the difference between that and the cone of protection thingy? OK, maybe a lopsided difuse beat up polygonal zone of protection.

Pat

I don't understand this too well, so have some difficulty explaining it.

For design purposes, you think of a ball with a radius of about 150'. Then roll that virtual ball across the terrain. Anything that it touches is a potential target. You place your lightning rods so the ball rolls over the rods and doesn't touch the structure.

So the zone of protection (in cross-section) is two arcs with a radius of about 150' that meet at the rod, forming a point. For a shorter structure this looks sort of like a cone.

I think the idea is that you assume that the leader comes down randomly until it is 150' away from a grounded object. At that point the streamer comes off the object and closes the circuit. That streamer is a radius of your virtual ball.

 

[hitekcountry]

The big difference with very tall structures (especially ones that are away from other tall structures) is that they can also get struck in the sides.

Makes perfectly good sense really. Ask yourself which travels faster the arc or the EMP. Then go back and read Patricks post #21 and you have your answer.

 

[shane]

I just got back to this thread. You know, I starting to think that the water in the shower is not the main problem.

 

[farmerjim]

i've seen 1st hand damages /death from lightning. when i was about 6 yrs old we were at empire farm days up near watertown ,ny and some storms came through during a field demo and some people thought it would be ok to take shelter under the equipment/ trees bad idea the lightning hit and i believe someone died, but some others were def injured badly. i also remember as a boy having it strike out on our driveway and come running through the shop floor where my dad was working on some hay eq. at work we get to see damage all the time it def can do some interesting stuff. i have a baseball size chunk of glass which was sand i got while working at a lightning hit one day.

 

[patrick_g]

Am I confused or are most of us basically in fair agreement?

Can't get a show of hands in this venue so I ask anyone who thinks that properly installed lightning protection systems do not reduce the probability of damage to state their reasons for that opinion.

We can exclude reasons like: I asked my insurance agent if lightning rods worked, I asked my insurance agent if I would get a discount, I asked the good ole boys at the recent meeting of the spit and whittle club, I asked some locals at the bar, you thought about staying a night at a Holiday Inn, and similar.

The science of lightning is an interesting field. Much is known but there is still a lot that is not well understood.

About the speed of a lightning bolt... it varies (uhh, it depends?) The EMP is propagated at the speed of light in the medium of interest (the extant atmosphere in the vicinity of interest.) The speed of the propagation of the lightning is slower. Even in excellent conductors like a fat copper wire, electrical signals travel at less than the speed of light. Its been a while since I looked at the tables but I don't recall seeing a conductor with a velocity factor greater than about 98% (velocity factor is the % of the speed of light that electricity in that conductor has.) The speed of light, although a universal CONSTANT is different in different media. Most generally when someone says THE SPEED OF LIGHT is invariant they are referring to the speed of light in free space or in some specified medium. Interesting stuff but another story.

Even though the lightning is not going the speed of light it is going way faster than anyones reflexes. When you see the lightning i.e. perceive the flash either you have already been hit by it or not and it is too late to do anything about it.

Pat

 

[patrick_g]

Emergency physicians at the Vancouver BC General Hospital wrote a report in the New England Journal of Medicine (July 12) in which they describe the extensive damages received by a patient who had been wearing an iPod (FryPod?) This guy was walking along and lightning hit a nearby tree. a pulse was generated in the wires going from the iPod to his ear buds. He was deafened in both ears and received burns where the wires were from both ears to where they joined by his torso and then to the iPod.

Usually you get flashover due to the resistance of the skin but with sweat and the wires this was circumvented and the energy was channeled up the wires to his ears. The electrical excitation to his nerves convulsed his jaw muscles and broke his jaw. They think explosive expansion of the air in his ears caused by conduction to the ear buds is responsible for the ear damage.

Last year a youth in Colorado sustained similar damage. Wearing ear buds or using an iPod doesn't increase the likelihood of getting electrified by a near miss but it does increase the severity of the event making it, dare I say it, much more electrifying.

So, if you decide to shower during an electrical storm and you have a waterproof iPod, maybe you should consider NOT WEARING IT.

Pat

 

[Grrrr]

Only just read this thread but we were once hit by a big lightening bolt.

We were having dinner with our neighbours house looking out over our house. It was very stormy outside and suddenly we see this massive ball of flame come along like a missile. Comes all the way up the road, flies round the corner towards our house and straight into the apex of the roof

We are all ***** ourselves wandering what was happening. We go down to our house and there is a 2 foot hole in the apex of our roof

There were big holes and channels everywhere there was once a phone line.

There are no phones to be seen but bits of phone gone through the plaster board

We got to the office where there were once to computers and now there are none. They had blown to pieces and flown against the plaster board. They had gone completely through the board and fallen down the gaps behind the board

Looked like someone had been firing a machine gun at our walls!

Anyway, lightening had hit an overhead phone wire and followed it along. It got to our house and then went in to the roof.

The phone lines on the telegraph poles had disentergrated.

We had the fire brigade out because there was a bit of smoke around and the mains wiring looked a bit hot.

Turns out we had to have the house completely rewired. The phone company had to replace miles of cable and a whole exchange! Two other houses had the same thing as us that night.

Glad we weren't in the house or I would probably be dead now

 

[patrick_g]

Jake, What an experience! Of course over on our side of the pond folks would have sued the phone company for not taking effective measures to protect their customers.

It could have been much worse. Someone could have been talking on a wired phone rather than cordless one and that would have not been a good thing.

What you were describing at first seemed to me to be the typical ball lightning effect but the effect was so very much more damaging than that usually associated with ball lightning.

Buildings can be rewired and repaired and the walls patched good as new but not so with us fragile humans. I think it was a stroke of luck that people weren't killed.

Pat