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Harvard Commentaries
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Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

The Real Dangers of Lightning

February 27, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Last reviewed and revised February 27, 2013

Advice abounds about how to avoid injury from lightning during a storm, but much of what you hear may not be reliable.

Because being struck by lightning is usually used as a metaphor for something that is exceedingly rare ("that's about as likely as getting struck by lightning"), it almost seems unnecessary to think about such a thing. But in fact, certain situations greatly increase your chances of being hit by lightning. And although the overall risk remains small, it is worth knowing how to reduce your risk if you find yourself in one of these situations.

The exact risk of being struck by lightning is difficult to determine. What is clear is that some settings are much riskier than others. For example, if you are caught in a lightning storm while outside in an open space, especially at an elevation (for instance, while hiking on a mountain trail), your risk is considerably higher than the estimated overall risk of 1 in 600,000. (That's according to the National Oceanic and Atmospheric Administration; other estimates vary from 1 in 10,000 to 1 in 5,000,000.)

Although rare, getting struck by lightning can be deadly. In the United States, lightning strikes kill an average of 82 people a year. And many more are injured.

Fact vs. Fiction

  • Don't take a bath or shower during a storm. Yes, you can get shocked if you are near pipes or faucets during an electrical storm, so experts recommend that you avoid taking baths or showers when lightning is striking nearby. You also should avoid being near bodies of water if you are outside during a thunderstorm.

  • Avoid using the phone during a storm. Using a phone with a cord during a thunderstorm is not a good idea because an electrical shock may be transmitted along the phone cord to you. In fact, the use of any electrical appliance should be avoided.

    Talking on a cordless phone indoors is not considered a high-risk activity, even during an electrical storm. However, using a cell phone outside should be avoided because the metal in the phone may act as a lightning rod.

  • Know how to calculate a storm's distance. If, after you see lightning, you count the seconds until you hear thunder, that amount of time is not equivalent to the number of miles away the storm is. Rather, you should divide the number of seconds by five. For example, if you see a lightning bolt and count 10 seconds before you hear thunder, the source of that bolt is about two miles away.

  • Don't take refuge under a tree. In fact, it is best to avoid being near tall objects (which are more likely to attract lightning) during a storm.

  • Don't huddle with others. If you are caught out in a storm, it is best to stay at least 15 feet apart from others to reduce the chances that any one person will be struck by a bolt of lightning. If you stay close together, multiple people are more easily injured by a single bolt.

  • Don't sit on the ground. If you are caught out in the open during an electrical storm, avoid sitting or lying down on the ground. Most lightning that injures people strikes the earth and travels through the ground; for this reason, the less contact you have with the ground the better.

    Ideally, you should avoid trees and other tall structures and avoid open spaces altogether. Seek shelter in a fully enclosed structure (such as a home, school or car). As a last resort, if you are unable to find shelter, crouch down low on the balls of your feet (to minimize contact with the ground).

  • Don't try to "read" the sky. If the sky is clear above you or the storm is far away, you can still be struck by lightning. Actually, "bolts from the blue" account for a significant proportion of lightning-related injuries. Because lightning may travel more than 20 miles before touching down, a storm can be in the next town and still cause injury or death. For this reason, experts recommend that you go inside when the source of lightning is six miles away or closer (that is, if the interval between lightning and thunder is 30 seconds or less) and wait until 30 minutes have passed since the last lightning or thunder struck before you resume outside activities (this is known as the "30/30 rule").

  • It is safe to help a lightning victim. One of the most prominent lightning-related myths is that you should not touch a lightning victim or you'll also be shocked. In fact, it is safe to help a lightning victim. Cardiopulmonary resuscitation and other forms of medical help may save them.

Be Careful

When the circumstances of a lightning-related injury are analyzed, it is often the case that some action on the part of the victim might have averted the injury.

For example, if you find yourself in a temperate climate with frequent thunderstorms, the last thing you should do is walk around open, hilly terrain with a metal rod. Yet golfers in Florida (where the largest number of lightning-related injuries and deaths occur) do this every day. Perhaps it is because they are not paying attention, they underestimate their risk or they are just unlucky.

To reduce your chances of attracting a lightning strike, recognize that you can do a few simple things to reduce your risk -- such as hanging up your phone if it has a cord.

For More Information

Colorado Lightning Resource Center, National Weather Service

National Lightning Safety Institute

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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