Flash Facts About Lightning
National Geographic News
|Updated June 24, 2005|
Organized by the National Oceanic and Atmospheric Administration
(NOAA) and other partners, Lightning Safety Week is held the last
full week of June each year.
Lightning is one of the leading weather-related causes of death and injury in the United States. Most people do not realize that they can be struck by lightning even when the center of a thunderstorm is 10 miles (16 kilometers) away and there are blue skies overhead.
Did you know that rubber shoes do nothing to protect you from lightning? That talking on the telephone is the leading cause of lightning injuries inside the home? That standing under a tall tree is one of the most dangerous places to take shelter?
And what does it mean if your hair starts to stand on end during a thunderstorm?
Scroll down for the answers to these and other questionsand for tips and procedures to protect yourself and your property against one of nature's most lethal phenomena.
Lightning is a giant discharge of electricity accompanied by a brilliant flash of light and a loud crack of thunder. The spark can reach over five miles (eight kilometers) in length, raise the temperature of the air by as much as 50,000 degrees Fahrenheit (27,700 degrees Celsius), and contain a hundred million electrical volts.
Some scientists think that lightning may have played a part in the evolution of living organisms. The immense heat and other energy given off during a stroke has been found to convert elements into compounds that are found in organisms.
Lightning detection systems in the United States monitor an average of 25 million strokes of lightning from clouds to ground during some 100,000 thunderstorms every year. It is estimated that Earth as a whole is struck by an average of more than a hundred lightning bolts every second.
The odds of becoming a lightning victim in the U.S. in any one year is 1 in 700,000. The odds of being struck in your lifetime is 1 in 3,000.
Lightning can kill people (3,696 deaths were recorded in the U.S. between 1959 and 2003) or cause cardiac arrest. Injuries range from severe burns and permanent brain damage to memory loss and personality change. About 10 percent of lightning-stroke victims are killed, and 70 percent suffer serious long-term effects. About 400 people survive lightning strokes in the U.S. each year.
Lightning is not confined to thunderstorms. It's been seen in volcanic eruptions, extremely intense forest fires, surface nuclear detonations, heavy snowstorms, and in large hurricanes.
Ice in a cloud may be key in the development of lightning. Ice particles collide as they swirl around in a storm, causing a separation of electrical charges. Positively charged ice crystals rise to the top of the thunderstorm, and negatively charged ice particles and hailstones drop to the lower parts of the storm. Enormous charge differences develop.
A moving thunderstorm also gathers positively charged particles along the ground that travel with the storm. As the differences in charges continue to increase, positively charged particles rise up tall objects such as trees, houses, and telephone polesand people.
The negatively charged bottom part of the storm sends out an invisible charge toward the ground. When the charge gets close to the ground, it is attracted by all the positively charged objects, and a channel develops. The subsequent electrical transfer in the channel is lightning.
If your hair stands up in a storm, it could be a bad sign that positive charges are rising through you, reaching toward the negatively charged part of the storm. That's not a good sign! Your best bet is to get yourself immediately indoors.
The rapid expansion of heated air causes the thunder. Since light travels faster than sound, the thunder is heard after the lightning. If you see lightning and hear thunder at the same time, that lightning is in your neighborhood. If you see successive strokes of lightning in the same place on the horizon then you are in line with the storm, and it may be moving toward you.
Not all lightning forms in the negatively charged area low in the thunderstorm cloud. Some lightning originates in the top of the thunderstorm, the area carrying a large positive charge. Lightning from this area is called positive lightning.
Positive lightning is particularly dangerous, because it frequently strikes away from the rain core, either ahead or behind the thunderstorm. It can strike as far as 5 or 10 miles (8 or 16 kilometers) from the storm, in areas that most people do not consider to be a lightning-risk area.
During a thunderstorm, each flash of cloud-to-ground lightning is a potential killer. The determining factor on whether a particular flash could be deadly depends on whether a person is in the path of the lightning discharge.
In addition to the visible flash that travels through the air, the current associated with the lightning discharge travels along the ground. Although some victims are struck directly by the main lightning stroke, many victims are struck as the current moves in and along the ground.
If you can hear thunder, you are within 10 miles (16 kilometers) of a stormand can be struck by lightning. Seek shelter and avoid situations in which you may be vulnerable.
Use the 30-30 rule, when visibility is good and there is nothing obstructing your view of the thunderstorm. When you see lightning, count the time until you hear thunder. If that time is 30 seconds or less, the thunderstorm is within six miles (ten kilometers) of you and is dangerous. Seek shelter immediately.
The threat of lightning continues for a much longer period than most people realize. Wait at least 30 minutes after the last clap of thunder before leaving shelter. Don't be fooled by sunshine or blue sky!
Most lightning deaths and injuries in the United States occur during the summer months, when the combination of lightning and outdoor activities reaches a peak. People involved in activities such as boating, swimming, fishing, bicycling, golfing, jogging, walking, hiking, camping, or working outdoors all need to take the appropriate actions in a timely manner when thunderstorms approach.
The Fourth of July is historically one of the most deadly times of the year for lightning in the U.S.. In summer, especially on a holiday, more people are outside, on the beach, golf course, mountains, or ball fields. Outdoor jobs such as construction and agriculture, and outdoor chores such as lawn mowing or house painting are at their peak, putting people involved in danger.
Where organized sports activities take place, coaches, umpires, referees, or camp counselors must protect the safety of the participants by stopping the activities sooner, so that the participants and spectators can get to a safe place before the lightning threat becomes significant.
People on or in or near water are among those most at risk during thunderstorms. Swimming is particularly dangerous, as not only do swimmers protrude from the water, presenting a potential channel for electrical discharge, but also because water is a good conductor of electricity.
Inside homes, people must also avoid activities which put their lives at risk from a possible lightning strike. As with the outdoor activities, these activities should be avoided before, during, and after storms.
In particular, people should stay away from windows and doors and avoid contact with anything that conducts electricity, including landline telephones. Most people hurt by lightning while inside their homes are talking on the telephone at the time.
People may also want to take certain actions well before the storm to protect property within their homes, such as electronic equipment. Surge protectors do not protect against direct lightning strikes. Unplug equipment such as computers and televisions.
If a person is struck by lightning, medical care may be needed immediately to save the person's life. Cardiac arrest and irregularities, burns, and nerve damage are common in cases where people are struck by lightning. However, with proper treatment, including CPR if necessary, most victims survive a lightning strike, although the long-term effects on their lives and the lives of family members can be devastating.
A house or other substantial building offers the best protection from lightning. For a shelter to provide protection from lightning, it must contain a mechanism for conducting the electrical current from the point of contact to the ground. These mechanisms may be on the outside of the structure, may be contained within the walls of the structure, or may be a combination of the two.
On the outside, lightning can travel along the outer shell of the building or may follow metal gutters and downspouts to the ground. Inside a structure, lightning can follow conductors such as the electrical wiring, plumbing, and telephone lines to the ground.
Unless specifically designed to be lightning safe, small structures do little, if anything, to protect occupants from lightning. Many small open shelters on athletic fields, on golf courses, in parks, at roadside picnic areas, in school yards, and elsewhere are designed to protect people from rain and sun, but not lightning.
A shelter that does not contain plumbing or wiring throughout or some other mechanism for grounding from the roof to ground is not safe. Small wooden, vinyl, or metal sheds offer little or no protection from lightning and should be avoided during thunderstorms.
There are three main ways lightning enters homes and buildings: a direct strike, through wires or pipes that extend outside the structure and into the ground. Regardless of the method of entrance, once in a structure, the lightning can travel through the electrical, phone, plumbing, and radio or television reception systems. Lightning can also travel through any metal wires or bars in concrete walls or flooring.
Phone use is the leading cause of indoor lightning injuries in the United States. Lightning can travel long distances in both phone and electrical wires, particularly in rural areas.
Do not lie on the concrete floor of a garage as it likely contains a wire mesh. In general, basements are a safe place to go during thunderstorms. However, avoid contact with concrete walls, which may contain metal reinforcing bars.
Avoid washers and dryers, since they not only have contacts with the plumbing and electrical systems but also contain an electrical path to the outside through the dryer vent.
Avoid contact with electrical equipment or cords. If you plan to unplug any electronic equipment, do so well before the storm arrives.
Avoid contact with plumbing. Do not wash your hands, do not take a shower, do not wash dishes, and do not do laundry.
Victims of lightning do not retain the charge and are not "electrified." It is safe to help them.
Rubber shoes will not give you any meaningful protection from lightning.
Lightning canand often doesstrike in the same place twice. Tall buildings and monuments are frequently hit by lightning.
A motor car with a metal top can offer you some protectionbut keep your hands from the metal sides.
An umbrella can increase your chances of being struck by lightning if it makes you the tallest object in the area.
Always avoid being the highest object anywhereor taking shelter near or under the highest object, including tall trees. Avoid being near a lightning rod or standing near metal objects such as a fence or underground pipes.
Most of the information on this page was adapted from the NOAA's National Weather Service's Lightning Safety Web site.
For more lightning coverage, scroll down
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