[geeks] Whee! Lightning strikes, AGAIN!

[Shannon Hendrix]

On Jul 30, 2009, at 19:22 , wa2egp at att.net wrote:

>> The lightning research community generally rejects the idea and
>> further says that it increases strike probability rather than  
>> reduce it.
>
>> From what I've read, "they" are not too sure either.

 From what I have read, they are very sure.

Tests with and without the systems on both existing and purpose built  
structures show they work.  The Space Shuttle was damaged many times  
until they started using a lightning rod.

>> Regarding sharp points.  New research indicates that round or blunt
>> points produce better intercept performance, and in the US all new
>> lightning rods are round or blunt.
>
> Gee, Maybe the sharp points dissipate the charge.

So do the blunt points, but that isn't why they protect against  
lighting.

None of them can discharge enough to work as you suggested.  What it  
does do is ionize the local are and create a field above that helps  
intercept strikes to bring them to a controlled ground.

You were saying that they bled off all the charge so the strikes would  
not happen, and no one has been able to do that.  There is no way to  
prevent strikes, at least not with any knowledge or technology we  
currently have.

Tall objects that create dissipation over wide areas do lower the  
amount of power in a storm, but even millions of trees have never been  
able to fully dissipate one.

> I read where he did not connect the wire on his first one to ground  
> but had it
> dangling in his chimney (I guess so he could do other experiments)  
> and touched
> it when a storm was nearing.
> I guess after he picked himself up, he decided to connect it to  
> ground. :-]

Who knows, I'm not sure we have the precise details.

>> Lightning dissipators are designed to prevent or reduce strikes, but
>> don't appear to work.
>
> I haven't seen any research saying either way but it would be  
> interesting to
> find out.  Can you cite any?

Google for NASA with related topics.  They tried to make them work and  
were never able to.

You can also easily find research projects for several purpose built  
lightning shelters, and dissipation systems have never worked.

Lightning rods work quite well, as do faraday cages, dielectric  
structures, steel exteriors (*), surge suppression systems, and good  
grounding systems.

* -> at least one shelter's outside is 1/4" steel, which of course is  
rather impractical for widespread use, but one of the projects is  
struck almost continuously as part of research, so it needs the  
protection.

>> They don't.  If there is no rod->ground connection, then it is not a
>> lightning rod.  See above.
>
> Oh yes they do.

When I say "they", I mean people who installing working systems which  
protect against lightning damage.

> I know of several buildings where this is done.  Of course
> this could be contractors not installing things correctly.  I live  
> in Jersey,
> get it.

Or you maybe can't see the grounding.

An ungrounded rod (or anything that creates a field and ionizes the  
air) is dangerous.

>>> If the frame takes the lightning strike, then why use lightning
>>> rods at all?
>>
>> To intercept the strike and bring it to a controlled ground.
>
> I know of some buildings with metal frames and metal roofs and still  
> have
> them.  Darn contractors again. :-]

A metal frame and roof has nothing to do with it.  Metal, wood, stone,  
plastic... you still need a good grounding system or the strike will  
take a path you don't want it to.

>> I'm sure if you ask someone who knows, you'll find they are grounded,
>> they are lightning rods.
>
> Find someone who knows.  Hmmmmm.  IIRC they are grounded and pointed  
> tips.

Then why did you say they were dissipators?

If they are grounded with pointed tips, they are old lightning rods.    
New ones are round or blunted.

> Actually there is a picture in a edition of a Haliday, Resnick and  
> Walker
> college physics book that shows a girl on a metal lookout platform  
> (taken by
> her boyfriend) with the typical hair all spread out from static  
> charge.  The
> text below the picture states that after the picture was taken, the  
> couple
> left and five minutes later lightning struck the platform.  Deaths  
> resulted
> (other tourists).  Now that would be a place to test lightning
> rods/dissipators.

A dissipator has already been tested there: it was the people on the  
platform.  Worked really good huh?

If the place had been properly grounded with a preferential strike  
point, they'd be alive most likely.

Unfortunately some tall structures are not, even after people have  
died there.


-- 
"Where some they sell their dreams for small desires."