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Name: T
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
My home was struck by lightening last week. A large tree in the yard (5 feet1 0 away was hit as well but luckily still standing) All the electrical outlets were damaged and light bulbs blown out of their sockets. Holes were torn in the eaves trough and a sensory light blown off the wall of the house. As well, the heavy duty stove electriclal cord was burnt through in two places even though the bracker had been turned off. I would like information about:

A) where would the lightening most lkely have hit first.?

B) how would the electrical sockets have been affected?

C) A specific explaination about what creates a lightening strike. and lightening in general.


Replies:
Dear Trudy-

Lightning strikes can produce some very strange effects, as you have observed first-hand. Lightning usually strikes the highest feature above the ground, but can "run" or jump to adjacent objects, such as houses, power lines, or even people or animals. Most like some of the lightning strike entered your home through the electrical circuitry.

Here is some more information concerning lightning for you Trudy.

Lightning is a fascinating phenomonon, one not totally understood by scientists. What HAPPENS during the initiation of a lightning stroke is fairly well recognized, and, thanks to high speed cameras, has even been caught on film several times. Lightning is responsible for more deaths each year (approx 200 in the U.S. annually) than either tornadoes or hurricanes. Many people are not aware of the hazard that lightning presents when they are outdoors in a thunderstorm.

Lightning can originate from the ground in the direction of the cloud, as well as strokes that originate within the clouds.

What is not totally understood is how the charge separates within the cloud, that leads to the electric field differential that triggers the formation of the conductivity channels within the atmosphere.

Here are some excellent websites that explain how lightning forms. Some are pretty basic, and a couple are more advanced. You might check these out.

Basic...

http://nimbo.wrh.noaa.gov/Portland/kidtopics.html

http://thunder.msfc.nasa.gov/primer/primer2.html

more detailed...
http://www.howstuffworks.com/lightning.htm

Wendell Bechtold, Meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO


Trudy,

This sounds like a classical strike to your electrical service (the AC line into your house). If it was raining at the time of the lightning strike, the lightning energy could even have come down the large tree first. It doesn't matter whether your electrical service comes into your house through the ground or via overhead lines. Lightning is good at penetrating the soil, especially if wet, and going into the electrical service line. From there it enters the house, blows right past the circuit breakers (circuit breakers do not protect you from electrical surges from outside the house, whether on or off), and goes through all of the electrical cable and fixtures in the house, often starting a fire in furniture, carpet, or the walls. What you described fits this pattern perfectly. This happened in exactly the same way to one of my neighbors ten years ago, and their house burned some as a result. Of course, as a lightning researcher and lightning protection system designer/inspector, I spent some time in the house assessing what had happened - a rare opportunity.

As to how lightning occurs, a thunderstorm builds up large areas of positive and negative electrical charge resulting from the friction of water droplets being lifted and dropped in the cloud. Even though air is a good insulator, eventually the charged areas become strong enough that a small stream of electrons (called a leader migrate from a positively charged area towards a negatively charged area.

Another leader comes from the negatively charged are to meet it. These ionize the air enough to give a conductive path and and negative electrons flow to the positively charged area to neutralize it. The flow of energy is so great that it actually causes the air to explode in a pressure wave and the energy also produces light. This is a lightning stroke, and can occur as a ground stroke or from one area of the thunderstorm cloud to another. Most of the molecules in the air at the site of the lightning stroke are blown apart by the huge amount of energy and then recombine into other molecules and pure atoms. A thunderstorm cloud actually has so much charge in it that it induces a buildup of charge on the ground under it. If the area on or near the ground area is large enough and intense enough, it becomes a preferred site for a lightning strike. Trees, chimneys, towers, etc. are prime targets as they are tall and can provide some distance of path that takes the place of the leader. They can also build up charge more easily, especially if not grounded. In our lightning research, we use a rocket to send a wire up into the air; this serves the same purpose as a wet tree or tall tower, by providing a path for the lightning energy; in this way, lightning is "triggered" and can be studied in a more controlled way.

David Cook


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