A lightning strike or lightning bolt is a lightning event in which an electric discharge takes place between the atmosphere and the ground. Most originate in a cumulonimbus cloud and terminate on the ground, called cloud-to-ground (CG) lightning. A less common type of strike, ground-to-cloud (GC) lightning, is upward-propagating lightning initiated from a tall grounded object and reaching into the clouds. About 25% of all lightning events worldwide are strikes between the atmosphere and earth-bound objects. Most are intracloud (IC) lightning and cloud-to-cloud (CC), where discharges only occur high in the atmosphere. Lightning strikes the average commercial aircraft at least once a year, but modern engineering and design means this is rarely a problem. The movement of aircraft through clouds can even cause lightning strikes.
Epidemiology
Lightning strikes can injure humans in several different ways:
Direct Direct strike – the person is part of a flash channel. Enormous quantities of energy pass through the body very quickly, resulting in internal burns, organ damage, explosions of flesh and bone, and nervous system damage. Depending on the flash strength and access to medical services, it may be instantaneously fatal or cause permanent injury and impairment. Contact injury – an object (generally a conductor) that a person is touching is electrified by a strike. Side splash – branches of currents "jumping" from the primary flash channel electrify the person. Blast injuries – being thrown and suffering blunt-force trauma from the shock wave (if very close) and possible hearing damage from the thunder. Indirect Ground current or "step potential" – Earth surface charges race towards the flash channel during discharge. Because the ground has high impedance, the current "chooses" a better conductor, often a person's legs, passing through the body. The near-instantaneous rate of discharge causes a potential (difference) over distance, which may amount to several thousand volts per linear foot. This phenomenon (also responsible for reports of mass reindeer deaths due to lightning storms) leads to more injuries and deaths than all direct strike effects combined. EMPs – the discharge process produces an electromagnetic pulse (EMP), which may damage an artificial pacemaker, or otherwise affect normal biological processes. Visual artefacts may be induced in the retinas of people located within 200 m (650 ft) of a severe lightning storm. Secondary or resultant: Explosions, fires, accidents. Warning signs of an impending strike nearby can include a crackling sound, sensations of static electricity in the hair or skin, the pungent smell of ozone, or the appearance of a blue haze around persons or objects (St. Elmo's fire). People caught in such extreme situations – without having been able to flee to a safer, fully enclosed space – are advised to assume the "lightning position", which involves "sitting or crouching with knees and feet close together to create only one point of contact with the ground" (with the feet off the ground if sitting; if a standing position is needed, the feet must be touching). Lightning strikes can produce severe injuries in humans, and are lethal in between 10 and 30% of cases, 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. Metallic objects in contact with the skin may "concentrate" the lightning's energy, given it is a better natural conductor and the preferred pathway, resulting in more serious injuries, such as burns from molten or evaporating metal. At least two cases have been reported where a strike victim wearing an iPod suffered more serious injuries as a result. During a flash, though, the current flowing through the channel and around the body can generate large electromagnetic fields and EMPs, which may induce electrical transients (surges) within the nervous system or pacemaker of the heart, upsetting normal operations. This effect might explain cases where cardiac arrest or seizures followed a lightning strike that produced no external injuries. It may also point to the victim not being directly struck at all, but just being very close to the strike termination.
According to the CDC there are about 6,000 lightning strikes per minute, or more than 8 million strikes every day. As of 2008 there were about 240,000 "lightning strikes incidents" around the world each year. According to the National Oceanic and Atmospheric Administration in 2012, over the twenty years to 2012 the United States averaged 51 annual lightning strike fatalities, making it the second-most frequent cause of weather-related death after floods. In the US, as of 1999, between 9 and 10% of those struck died, with an annual average of 25 deaths in the 2010s decade (16 in 2017). In the United States in the period 2009 to 2018 an average of 27 lightning fatalities occurred per year. In the United States an average of 23 people died from lightning per year from 2012 to 2021. Some people suffer from lifelong brain injuries. As of 2005, in Kisii, Kenya, some 30 people die each year from lightning strikes. Kisii's high rate of lightning fatalities occurs because of the frequency of thunderstorms and because many of the area's structures have metal roofs. As of 2013, direct-strike casualties could be much higher than reported numbers. In 2015 it was reported that between five and ten deaths from lightning occur in Australia every year with over 100 injuries occurring. In 2018, it was reported that "a direct strike accounts for only 3 to 5 percent of all injuries and death, while ground currents, which spread out over the ground after lightning strikes, account for up to 50 per cent... ...Where the lightning strikes the ground, the ground becomes highly electrified and if you're within that area of ground electrification..." you can receive an electrical shock from the lightning. In 2021, one report wrote that "30-60 people are struck by lightning each year in Britain, and on average, 3 (5-10%) of these strikes are fatal." It also estimated that "...one in four people struck by lightning were sheltering under trees."
Effect on animals
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