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Name: Michel
Status: student
Age: N/A
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Date: N/A


Question:
I read that when lightning strikes the voltages generated vary from 10 million to 120 million volts. We know that such high voltages ionize the air mostly nitrogen. We also know that carbon, hydrogen, and oxygen which are major constituents of our body have lower ionization energies than nitrogen. So, when lightning hits a lightning rod is the electromagnetic field around the rod strong enough to ionize carbon, hydrogen, and oxygen in our bodies? If so, up to what distance from the rod? I asked this question to a physicist and to a chemist at University of Ottawa, Canada, and to a specialist of high voltages at Hydro-Quebec but I did not receive any answer. That makes me think they do not know and that is why I am writing to you.


Replies:
There are several things going on here, all happening very fast. The field around the lightning discharge is not uniform, and the lightning bolt is preceded by a leader that strikes "up" not "down". This all happens on a microsecond time scale, making experimental observations difficult. The details of this preliminary breakdown is not well understood, and itself may be a sequence of events. All of this may happen too fast for the surrounding air to breakdown, since that process depends upon the mean free path of the surrounding molecules. The accompanying thunder is supersonic. Your sources may just be showing "good judgment" by avoiding an oversimplified explanation. If you want to get some idea of just how complicated a lightning discharge can be, refer to the book "The Lightning Discharge" by Martin A. Uman published by Dover Publications 2001. It is thorough but not easy reading.

Vince Calder


Michel

Here is a background article about Ionizing Radiation:

http://en.wikipedia.org/wiki/Ionizing_radiation

Here are some excerpts:
"Ionizing radiation consists of particles or electromagnetic waves energetic enough to detach electrons from atoms or molecules, thus ionizing them. The degree and nature of such ionization depends on the energy of the individual particles or waves, and not on their number. An intense flood of particles or waves will not cause ionization if these particles or waves do not carry enough energy to be ionizing. Roughly speaking, particles or photons with energies above a few electron volts are ionizing. Ionization produces free radicals, which are atoms or molecules containing unpaired electrons, that tend to be especially chemically reactive due to their electronic structure."

"Lower-energy radiation, such as visible light, infrared, microwaves, and radio waves, are not ionizing.

The latter types of lower energy electromagnetic radiation may damage molecules, but the effect is generally indistinguishable from the effects of simple heating. Such heating does not produce free radicals until higher temperatures (for example, flame temperatures or "browning" temperatures, and above) are attained."

"Free radical production is also a primary basis for the particular danger to biological systems of relatively small amounts of ionizing radiation that are far smaller than needed to produce significant heating. Free radicals easily damage DNA, and ionizing radiation may also directly damage DNA by ionizing or breaking DNA molecules."

This marks the end of the excerpts, but if you are interested you should read the entire article.

The lightning bolts radiate electro-magnetic waves over a broad frequency range. Please see this URL for an explanation of the electro-magnetic frequency spectrum:
http://en.wikipedia.org/wiki/Electromagnetic_spectrum

Here is a video that might improve your understanding:
http://mrhardy.wikispaces.com/Electromagnetic+Spectrum.swf

To address your question: Radiation is radiated from a lightning rod cable, but the energy of those particles have not been measured, and the energy level of those particles will determine what biological harm will result.

I am not a lightning researcher or a medical person, but I am a senior electronics engineer with an interest in lightning effects and I have never heard of anyone getting radiation poisoning or flash burns from a cable carrying current from a lightning strike or any other current source. I have seen videos of researchers standing in Faraday cages with lightning flashing all around them with no biological effects. The very short-duration of the lightning strike probably has a lot to do with this but here is a video that shows a subject standing in a Faraday cage being exposed to electric arcs with no biological effect demonstrating that the radiation from an electric arc does not radiate enough energy to even cause a flash burn:

http://www.youtube.com/watch?v=Zi4kXgDBFhw&feature=related

Sincere regards,

Mike Stewart


Michael,

I think there are lots of reasons that work against your speculated ionization.

I think the millions of volts never really show up along the length of the rod, because it is a conductive metal. They exist across kilometers of air, until the moment the breakdown starts, and then there is inductive drop across that same kilometer-long path length,

Due to inductance of a straight conductive path (i.e., a wire or rod) there might be some tens or hundreds of thousands of volts along the rod, at the moment the strike reaches the rod and starts to build up current. At most, it would be roughly in proportion to the ratio of lengths of the lightning arc vs. the rod's length. (Think 4meter/4km * 50Mv = 1/1000 * 50Mv = 50kV. And that is at negligible radius from the rod.) It would only last for microseconds, only as long as the rise time of the current. If for some reason the current increase took longer, the voltage would be proportionately less.

Induced fields around a discharge path are quite dangerous to electronics, and can electrocute you, but ionizing watery flesh is another order of magnitude altogether. Quite difficult to do. Water is much denser than air, so it is much more difficult to start sparks in it. In a dense substance, each free electron has less available distance to fall before bumping into the next atom it must ionize. If air takes about 10kv/mm to spark, water takes closer to 100kv/mm. And that water is conductive due to 3% salt content , and has a high dielectic constant of ~100, so a brief impulse is very likely to be shunted through without ever creating kv/mm fields. Also, that body is probably surrounded by air which would oppose the induced current. Think which way the current would be driven. If a vertical body is near a vertical pole, the induced voltage would be vertical, and current would need to enter the head and leave the feet (or v/v). Often there is a conductive path from the feet, but usually not from the head. There would be no significant current unless there was a visible spark from the head to some other structure. Unless the head is rather near something conductive, induced voltages of 200kv to 1Mv would be needed, and usually not quite available.

Maybe you could not get an answer because this damage mechanism is huge overkill that nobody's had much reason to think through before. Electrocution kills you first, and current-heated flesh second. Spark-discharge within your tissues would be a distant 3rd or 4th, far beyond the onset of lethal damage, and generally well beyond practical probability of occurrence too.

I am taking voltage-induced ionization within a dense material to be synonymous with "avalanche breakdown" and "dielectric breakdown" and "spark discharge". If you want to know something about "dielectric breakdown in water", I think that would be the phrase to research. As examples, I think water-filled spark-gaps have been tried for things like Nitrogen lasers.

Oh, I did once read that because the body can be considered conductive watery zones riddled with non-conductive fatty tissues, that there might be microscopic current-necks which create high potentials at minute points of ionizing breakdown, all at surprisingly low RF fields. The article speculated that subtle body damage from these might prove to be a real reason for lower regulatory RF exposure limits. So despite my diatribe above there might well be tiny amounts of ionization during a strike at close proximity. It merely might not kill you, and you would not necessarily know it happened.

Jim Swenson



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