Posted on 06/22/2006 11:32:56 AM PDT by Mr. Brightside
Today: June 22, 2006 at 9:56:7 PDT
Lightning Strike Kills Colo. Motorcyclist
ASSOCIATED PRESS
WESTMINSTER, Colo. (AP) - A motorcyclist died after he was struck by lightning while riding in rush hour traffic between Denver and Boulder, police said.
Witnesses reported seeing a flash of light shortly before the motorcyclist struck the center divider on U.S. 36 Wednesday, police spokesman Tim Read said.
Gary Missi, 46, of Longmont was pronounced dead at the scene.
A coroner's investigation was under way to determine whether the lightning bolt, the collision or something else caused his death, Read said.
The lightning blasted a 4-inch-deep hole in the highway and sent chunks of asphalt hurtling across the highway.
--
Shocking.
I knew motorcycles were dangerous!
It's not exactly a Faraday cage. It's called the skin effect. Faraday is for stationary charge, skin effect is for an actual current, that is, flowing charge. Some good links there.
See my post #78, correcting my own confusion of the two.
Of course I do. But logic doesn't matter to the nanny statist.
The latest research shows that blunt lightning rods work better than sharp ones. In one test, twelve of the blunt rods were struck and none of the nearby sharp ones were.
(Also, people used to think that lightning rods allowed a slow leakage of charge and therefore actually prevented strikes. This has been shown to be incorrect. A thumbtack on the top of the sphere of an electrostatic generator will leak enough charge to strongly reduce the length of sparks.)
Generally when a car is hit only a rather small bolt is involved. That's, because in the case of a car, their are other features around that take up charge and could be hit. It could be other cars in the area. The car in the pic had it's winshield blown out, because the wiper had the highest value for the electric field on the car. The wiper couldn't carry the current, so the current took the path of arcs though the window at the 2 ends of the wiper. That's the reason the biker has hit, rather than the other cars in the local area. The bike had more than a few "points" on it where a high field existed.
Wow, we need to tell the guys at the Richmond Science Museum . . . < g >
(. . . the roll bar was installed by my dad, because he didn't trust our teenaged driving abilities. As I told him, hey, I was hit by lightning and didn't freak and run right off the road, what more do you want?)
That depends. Their suggestion is that one assume the shape of a ball on the ground. The reason to lie flat is that one has the clue of an immanent strike. That is, before the strike the person senses the charge accumulating on him. There's a distinct tingling sensation and the hairs stand up. Taking a ball position won't help. The buildup will continue and the strike will hit you anyway. Laying flat reduces the electric field intensity on the person to that of the local ground. There's no I*R drop there. That sharply reduces the probability of being struck.
In the case of the condition in the articles posted, the key feature is voltage drop(I*R) in the ground some point away from the object collecting the charge that's developing the high field. If one was really sweaty, with a lot of salt on them, laying on the ground would provide an alternate high conductivity path for the current on it's way to the dischage point(which was never the person). It was a nearby tree, or metal building for instance. The key points would be ground conductivity and the magnitude of the impending strike.
"The latest research shows that blunt lightning rods work better than sharp ones. In one test, twelve of the blunt rods were struck and none of the nearby sharp ones were. "
Pointed rods are always better. The field intensity at a point provides for field emission of electrons that reduce the local field and dissipate the charge. Either electrons are emitted, or a plasma forms and they're collected. That reduces the intensity of the impending strike. It might even prevent it. Field emission at blunt tips effectively doesn't happen and they just get hit.
Yes, even science museums are slow to pick up on new findings.
My hubby is a radio amateur (actually, I am too, but he's the serious DXer - Honor Roll and all) and I was an arson investigator years ago (I had to be able to tell the lightning from the arson!) so we have more than an academic interest in this stuff . . .
Here's the research on the blunt rods from the Journal of Applied Meteorology: Vol. 39, No. 5, pp. 593–609.:
http://ams.allenpress.com/amsonline/?request=get-document&doi=10.1175%2F1520-0450(2000)039%3C0593:LRIS%3E2.0.CO%3B2
For those who want a shorter version, just read the first part of the above paper or try this:
http://www.usatoday.com/weather/resources/basics/2000-05-15-lightn-rod-tests.htm
Alone on the top of a rise, I would probably lie flat if I get signals from the electric field. In an open flat field I'm going to crouch. There are a number of stories online where baseball, football, and soccer teams are on a field and the lightning hits one of them or the ground rather than one of them and several are killed by the ground streamer. The crouch would have saved them.
ALL of you experts on this thread stating sources and providing cites and graphs invariably depend on at least two extra factors: time and current path. As I said the statement as originally made is not universally true and I don't buy it; there are other factors involved. The original statement of 10s of mAs is equivalent to saying " 100 miles PER is extremely dangerous and will kill you." I'll leave the equivocation to you experts....
Just go back and look at your reply and count all of the conditions required for your reply to refute what I originally said. Time and current path among the two chief factors, others are voltage, type of voltage, a myriad of factors. Blanket statements like 10s of mAs can/will kill are just like saying 100 Miles/Per (no time factor) is dangerous.....
Are you saying that current times time gives charge and charge alone isn't what kills? If so, I agree.
But, if we assume that a given current is through the average human heart, this current produces chemical changes in the heart and these are what cause the fibrillation or paralysis that eventually leads to death. We can't look at this as we would a piece of wire. There are several factors, but, since most hearts are biologically pretty similar, the results should be roughly the same.
If we pass a certain current for a short time, the chemical changes made are small and reversible. If we increase the time, the changes become larger and less reversible. Beyond a certain time, the changes interrupt the function of the chemical system of the heart. It starts to fibrillate.
Similar to putting a finger on a hot stove. Short time, minimal damage. Long time, tissue is destroyed.
There will be heating, too, which will also cause chemical changes. The heat energy released per second is power. Electrical heating is determined by power = i^2 times R. So, if we know the tissue resistance and the current, we can determine the joules of heat energy per second dumped into the tissue.
Am I hitting what you are looking for yet?
Basic theory which was proven by Ben Franklin.
(Also, people used to think that lightning rods allowed a slow leakage of charge and therefore actually prevented strikes. This has been shown to be incorrect. A thumbtack on the top of the sphere of an electrostatic generator will leak enough charge to strongly reduce the length of sparks.)
I would be interested in seeing the where that has been shown to be incorrect.
Your theory is correct but many lightning protection systems are designed to be hit.
I think those factors were also addressed.
One of my Mom's old weather lore maxim's.
When the cow's lay down it's going to rain.
Maybe it's mass suicide.
The latest research shows that blunt lightning rods work better than sharp ones.
You said:
Basic theory which was proven by Ben Franklin.
Hmmm.
http://www.physicstoday.org/vol-59/iss-1/p42.html
In his first letter, Franklin described "the wonderful Effect of Points, both in drawing off and throwing off the Electrical Fire." He showed that points work quickly at "a considerable Distance," that sharp points work better than blunt ones, that metal points work better than dry wood, and that the pointed object should be touched—that is, grounded—to obtain the maximum draw effect.
I'm just reporting research. Maybe Franklin was wrong. Maybe they are wrong. Time will tell. As for your second part, I can't reply now. Have to go see 91-year-old father-in-law.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.