Lightning is the visual flash associated with a rapid discharge of electrical energy into the atmosphere. During a thunderstorm, cold temperatures cause the formation of ice crystals inside storm clouds. A negative electrical charge builds inside the cloud and a positive charge builds on the ground below. The positively charged particles begin to travel upward along trees, houses, telephone poles and other tall objects. At the same time, the negative charge is drawn downward to the positive charge. The visible flash of lightning occurs when the negative charge meets the positive charge. Katie Fehlinger, Weather Broadcaster with AccuWeather.com in State College, PA, says lightning can also travel from cloud to cloud or within the same cloud. Heat lightning is not caused by heat, but by a thunderstorm too far away for the sound of the thunder to be heard.
According to the National Weather Service, more than 1,800 thunderstorms occur at any given time somewhere on the planet. A single bolt of lightning can be as hot as 50,000 degrees F and contain 100 million volts of electricity. Lightning can strike as far as ten miles from a storm. The thunder that accompanies lightning is actually sound created by the explosive force of the lightning. Thunder and lightning go hand-in-hand, though lightning may be too far away to be seen.
The Federal Emergency Management Agency (FEMA) estimates the risk of being struck by lightning is one in 600,000. Still, about 300 Americans are injured by lightning annually. In 2009, the National Weather Service registered 34 deaths from lightning strikes. So far this year, two deaths have been recorded (one in Indiana and one in Connecticut).
Lightning can cause an injury in one of four ways. A direct strike happens when the pathway for the electrical charge travels through the body. It causes the most serious type of lightning injury. However, Mary Ann Cooper, M.D., Emergency Physician with the University of Illinois at Chicago, says direct strikes only account for about five to ten percent of all lightning injuries. In a side flash (also called a spray or splash), the lightning hits another structure and the energy is conducted through the air to someone standing nearby. Researchers say this is the most common method of injury in lightning strikes. A ground strike occurs when lightning hits the ground and the current fans out and is conducted through the legs of a nearby victim. This is another common method of lightning injury. The fourth method of injury is a flash-over. The energy from the lightning flows around the body. Sweat or moisture from rain conducts the electricity, causing the surrounding air to rapidly expand in an explosive blast.
Despite the high temperature of lightning, victims rarely have burn injuries. Cooper says that’s because the flash is so quick and most victims are hit indirectly. The most common type of injury associated with a lightning strike is rupture of the ear drum, caused by the intense force of the thunder shock waves. Lightning is also likely to cause neurological injuries, leading to long-term symptoms, like chronic pain, fatigue, problems with attention and memory, personality changes, sleep disorders, dizziness, muscle weakness and depression.
Most lightning injuries occur because people are caught off guard, don’t heed warnings or fail to find appropriate shelter during a storm. Storms can move quickly or appear to “come out of nowhere.” A severe thunderstorm watch means conditions are right for a severe thunderstorm and thunder and lightning are likely to occur. A severe thunderstorm warning means that severe weather has been spotted in the area or detected by radar.
The rule of thumb for lightning safety is, “If thunder roars, go indoors.” Stay inside the house and don’t touch a corded telephone, wires, plumbing or other objects that can carry an electrical current if lightning strikes on or near the home. Stay inside for at least 30 minutes after the last sound of thunder. If you are caught outside when a thunderstorm is approaching, take shelter in a hard top automobile (not a convertible). Contrary to popular belief it isn’t the rubber tires that protect you from a lightning strike, but the metal shell of the car.
If you are in the open and you feel your hair standing on end, it means a nearby lightning strike is imminent. Lightning tends to strike at the tallest object. Do not hide near a tree. If you can’t get to an immediate shelter, squat as low to the ground as you can while standing on the balls of your feet. Place your hands over your ears to protect them from the explosive sound waves that accompany a lightning strike. Do not lie flat on the ground.
Federal Emergency Management Agency, http://www.fema.gov
National Lightning Safety Institute, http://www.lightningsafety.com
National Weather Service, http://www.lightningsafety.noaa.gov
Kleiter, Ingo, et al., “A Lightning Strike to the Head Causing a Visual Cortex Defect with Simple and Complex Visual Hallucinations,” Journal of Neurology, Neurosurgery and Psychiatry, April 2007, Vol. 78, No. 4, pp. 423-426.
Mistovich, J., et al., “Beyond the Basics,” EMS Magazine, March 2008, Vol. 37, No. 3, pp. 82-87.
Offiah, C., et al., “Lighting Strike,” AJNR: American Journal of Neuroradiology, May 2007, Vol. 28, No. 5, pp. 974-975.
Zafren, K., et al., “Lightning Injuries,” Resuscitation, June 2005, Vol. 65, No. 3, pp. 369-372.