January 19, 2012 by staff
Lightning Strikes, Lightning strikes are electrical discharges caused by lightning, typically during thunderstorms.
Humans can be hit by lightning directly when outdoors. Contrary to popular notion, there is no ‘safe’ location outdoors. People have been struck in sheds and makeshift shelters. However, shelter is possible within an enclosure of conductive material such as an automobile, which is an example of a crude type of Faraday cage.
World map showing frequency of lightning strikes, in flashes per km² per year (equal-area projection). Combined 1995-2003 data from the Optical Transient Detector and 1998-2003 data from the Lightning Imaging Sensor.
The Eiffel Tower as a colossal lightning conductor. Photograph taken at 21.02 1902-06-03
An estimated 24,000 people are killed by lightning strikes around the world each year and about 240,000 are injured. In the U.S., between 9 and 10% of those struck die, for an average of 40 to 50 deaths per year (28 in 2008). In the United States, it is the #2 weather killer (second only to floods). The odds of an average person living in the U.S. being struck by lightning in a given year is 1/500,000.
U.S. National Park Ranger Roy Sullivan has the record for being struck by lightning the most times. Sullivan was struck seven times during his 35 year career. He lost the nail on one of his big toes, and suffered multiple injuries to the rest of his body.
Lightning strikes injure humans in several different ways:
Direct strike, which is usually fatal.
Contact injury, when the person was touching an object that was struck
Side splash, when current jumped from a nearby object to the victim
Ground strike, current passing from a strike through the ground into a nearby victim. A strike can cause a difference of potential in the ground (due to resistance to current in the Earth), amounting to several thousand volts per foot.
Blast injuries, either hearing damage or blunt trauma by being thrown to the ground.
Lightning strikes can produce severe injuries, and have a mortality rate of between 10 and 30%, with up to 80% of survivors sustaining long-term injuries. These severe injuries are not usually caused by thermal burns, since the current is too brief to greatly heat up tissues, instead nerves and muscles may be directly damaged by the high voltage producing holes in their cell membranes, a process called electroporation.
In a direct hit the electrical charge strikes the victim first. If the victim’s skin resistance is high enough, much of the current will flash around the skin or clothing to the ground, resulting in a surprisingly benign outcome. Metallic objects in contact with the skin may concentrate the lightning strike, preventing the flashover effect and resulting in more serious injuries. At least two cases have been reported where a lightning strike victim wearing an iPod suffered more serious injuries as a result. However, during a flash the current flowing around the body will generate large magnetic fields, which may induce electrical currents within organs such as the heart. This effect might explain the cases where cardiac arrest followed a lightning strike that produced no external injuries.
Splash hits occur when lightning prefers a victim (with lower resistance) over a nearby object that has more resistance, and strikes the victim on its way to ground. Ground strikes, in which the bolt lands near the victim and is conducted through the victim and his or her connection to the ground (such as through the feet, due to the voltage gradient in the earth, as discussed above), can cause great damage.
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