Effect and Mechanics of Lightning Strike

You may not have much choice, but can you request a better insurance assessor?

Short circuit currents and other such transients can induce large magnetic forces capable of moving cables and busbars into or away from each other. Rapid heating of moist areas could generate steam at explosive pressures. But even if a fire is started, the oxidation process would not be so rapid as to create a large vacuum (maximum of 6" Hg even if all the oxygen were instantly consumed).

Hi, Hendrik, Glad they are ok.
Dunno what the mechanisms are, I expect theyve done some scale model high voltage discharge tests at some time...I mean if you worked in an establishment that had a HV machine you'd just have to do it wouldn't you? Zapp your Action Man or Barbie too I expect
Del

Good that they're OK.

I know what they must have gone through. I was sat in my local pub when it and the house next door were struck. The house took the brunt of it causing a minor fire, all wiring and appliances fried.
I was sat at the bar with one eye on the television news when all 3 televisions around the bar exploded, the satellite system caught fire and the jukebox was a smoking wreck. Strange thing is all the fixed wiring survived.
Good job they serve "real" ale, I could carry on drinking.

The superheated plasma (air blast) alone is enough to severely damage walls and ceilings (especially old plaster).

The primary mechanical/structural damage comes from the discharge vaporising even the smallest traces of water to steam with explosive results. We used Megavolt Marx Banks (tiny energy compared to actual lightning) on typical construction lumber and cement based building products. The stud lumber bursts into toothpick sized splinters and concrete block just explodes period. I'd expect to see twisted or melted nails and fasteners, but we didn't test those because of inadequate ballistic shielding.

Your adjuster may know claims values, but he should leave the scientific explanations to people who actually know a little about the topic.

GA.

Especially the part about moisture content of materials being turned into super-heated steam. I've seen plenty of trees where the lightning strike blasts off the bark due to that same process. When our neighbors tree was hit by lightning about two years ago, I found pieces of bark in my back yard, 50 to 60 feet away from the tree that took the direct hit. We lost a number of electronic items on that side of the house just from being in the vicinity of the strike. All in all, we were lucky we didn't sustain greater damage or injuries.

The experts don't all agree upon things so I would not automatically assume that the insurance assessor knows everything.

The process started (the part you are not asking about) with a corona path upward from something that is often high and/or often sharp. This could have been the house, a nearby tree, a TV antenna tower, whatever. Then, you probably had some more significant current rise upward toward the cloud in a somewhat jerky manner. After that, you probably had from one to seven or eight "flickering flashes". If the discharge was from the bottom of the cloud then it was probably negative charge and if the discharge was from the top of the cloud then it was probably a positive discharge. This all could have taken about a second, more or less, which is a pretty short time but it might be longer than many people would have guessed

As the above was taking place the wind might have been blowing. The corona path may have started somewhere upwind and been blown 5 to 15 feet onto the top of the house by the time (probably less than one second) that the big bolt started to flow.

In terms of the damage it is not possible for most of us to understand the power of a little superheated steam. My neighbors tree was hit once and a 1" x 3" x 0.75" piece of bark flew about 75 feet and knocked a 2.5" x 6" hole in a 1x6 fence board (rather new board, was in good shape).

The electromagnetic pulse of a lightning strike is strong, but I would be a little slow to accept that it threw the nails across the room. Frying equipment throughout the house is very realistic, even if the energy was induced and not directly conducted.

As for the missing part of your roof, did you check in the bushes two or three houses down?

Bruce

I understand why you want to know what happened; however, I'm a little confused about the insurance company. Are they, or is he, saying that you are not covered?

While it's nice to propose a theory, you want the insurance company to make you whole.

Get a second, and perhaps a third, opinion. For the Supreme Creator's benefit, don't sign on the dotted line until you are satisfied!!!!!!

Good Luck in the contest.

A radio operator who has suffered a EMP

Thanks Bruce & all

The ceiling is gypsum board nailed onto brandering nailed onto the wooden beams.

The ceilings of all the rooms bulged out and some of the about 30mm nails pulled out.

Maybe the assessor will say the policy do not cover damage caused by vacuum - we will wait and see.

The satellite dish was in on the fun (although not directly hit) The face plate (about 100 x 100mm) on the outlets on both floors was blown of. The pvc covering on the coax to the decoder flared open. The decoder show heat / burn marks and was fried on the inside.

Even the radio linked PIR alarm sensors is out.

The TV was on but survived because it was coupled via the decoder/DVD.

I have an eyebolt that was the anchor for an insulator of an 8kV utility line. Where the eyebolt and insulator made contact the eyebolt is oxidized and non-conductive for about a 1/4" area, the top of the pole was burnt. In the non-conductive area of the eyebolt there was arcing to the insulator base and in the insulator causing Radio-TV interference.

James R Booker said lightening can do anything it wants to, he had a bolt with a 3/4" diameter hole burned the length of it.

An interesting finding recently was that at the base of the arc there are x-rays, coupled with the ozone from the ionized air and materials, and the UV light from the lightening bolt. There is some research that exposures (combined with and for how long) may have connection to Lou Gehrigs Disease or others. Electric arc welders would be exposed to this frequently, along with high voltage line repairmen and electric substation workers if this is true, which electric field intensity and maybe magnetic field, versus the person being near a lightening bolt of some magnitude which would need to exceed some as yet undefined threshold. Not defined is the key word.

Air is a mixture of gases - 78% nitrogen and 21% oxygen - with traces of water vapor, carbon dioxide, argon, and various other components, accordingly a total extraction of oxygen ( 21% constituant) from air even if it ocours simply cannot create vacum thus the insurance guys are just throwing jargon in their vested interests.

During a thunder storm a cloud gets charged and induces an opposit charge on earth, when the gradient reaches 5000 to 10000 volts per cm flash of lightning starts from cloud to earth (or to another clod as the case may be) with a speed of 0.5 % that of light or approximately 30 cm per micro second, as the pilot reaches the earth electrostatic field increses a streamer shoots up from the earth as well.

A lightning strike which appears to the eye as a single flash is a number of strokes with a time interval of 0.005 to 0.5 seconds.

The lightning stroke being of vevy high gradient and v high frequency has the inherent cheresterstics to travel through shortest or a path of lest resistance hence after striking at a certain point can jump across air gaps inside a building.

A tall structure (building) would provide protection to smaller adjescent buildings if these happen to fall in a zone under an angle of 45 degrees from the top of the taller structure otherwise in areas of high lightning probablity any building would require a lightning protection to save from damage ( Grids and transmission lines have lightning protection in the form of ground wire conductors atop).

I suppose if your house does get hit by a lightning bolt all sorts of nasties can happen............but vacuum.............I think not. Were windows blown into the house, which I think would have had to occur if a vacuum was created inside the house, particulaly if, the the said vacuum, was responsible for the other damage!!!

Not so long ago a student of mine bought a brand new 20m cray boat, and we had rather a fierce thunderstorm and unfortunately his vessel received a direct hit from a bolt of lightning, which destroyed every piece of electical equipment on board including radar, sonar, engine sensors, gauges, electronic control gear, lighting and power circuits, etc............the boat had a lightning conductor and ground plate. The boat was a 6000 series aluminium/alloy construction.........there was no gripes at all from the insurance company.

It would probably not even be 20%, may be more like 15% or even lower.........and whether or not a prduct of incomplete combustion, CO, would have had time to ignite maybe questionable........bearing in mind the time period over which the event takes place.

Just a thought...........not based on any empirical knowldge that I have.

While I believe that lightning was responsible for the damage,I don't believe the adjustor's explanation of the physics of failure. The important thing is to determine whether it's required for you to understand the physics, or whether you just want to satisfy your curiosity. I use a rather outdated publication "Lightning and Lightning Protection" by William Hart and Edgar Malone. Library of Congress Card Number 79-65691. "The destructive power of lightning arises from the high pressure generated in the lightning channel. In open air, energy deposited by a single stroke is in the order of 10e5 joules per meter. This is equivalent to approximately 22g of TNT per meter, or one tenth of a ton of TNT, for the average channel."

Hopefully your adjuster was just making light conversation and your insurance company will step-up and cover the cost of all appropriate repairs.

Direct lightning strikes can reach 5000 to 100000 Amps and release up to 500 Mega-Joules of energy. By comparison, Pulsed Power toys like Coin Shrinkers , Marx Banks, Rail Guns, Coil Guns, etc., have similar peak currents, but release only a small fraction of that energy. All of these devices can easily vaporize metal and throw shrapnel at supersonic velocities. While educational and occasionally fun to play with, they are lethal in many ways and must be treated with great respect.

My point is that the electromagnetic forces of a direct lightning strike can be orders of magnitude higher than most people think. While explosive vaporization forces may typically cause the most damage in home strikes, one should not dismiss the electromagnetic forces.

Note: Newest experimental railguns are up to ~30 Mega-Joules projectile kinetic energy. Impressive, but still small compared to mother nature.

To prevent next strike put a steel wrope along the roof and connect it to ground. This would take the shop and prevent damages to the house. Very effective protection, but sometimes the rope just melts if the lightning carried more than usual charge.