Chapter 3 Lightning Injuries
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Lightning has caused injuries to humans since humans evolved on Earth. It has played a major part in nearly every ancient religion and culture. Priests, some of whom were the earliest astronomers, also became proficient at weather prediction, interpreting changes in weather as omens of good or bad fortune, sometimes to the advantage of their political mentors. To this day, it continues to engender stories, perceptions, and myths and is a popular topic for the press and science and weather documentaries.114,234
Lightning was often depicted in the art of ancient cultures and religions and has long been feared as an atmospheric flash of supernatural origins. A roll seal from Akkadian times (2200 BC) portrays a goddess holding sheaves of lightning bolts in each hand. Next to her, a weather god drives a chariot and creates lightning bolts by flicking a whip at his horses, while priests offer libations. A relief found on a castle gate in northern Syria (900 BC) depicts the weather god Teshub holding a three-pronged thunderbolt (Figure 3-1, online).
Beginning around 700 BC, Greek artists began to incorporate lightning symbols representing Zeus’s tool of warning or favor. Zeus, as the king of the gods, could control the weather. Early Greeks believed that lightning was his weapon and that when lightning struck Earth, it was a direct sign of Zeus’s presence or influence. The ancient Greek poet, Hesiod, called him the “cloud-gatherer” and the “thunderer.” Zeus was also concerned with hospitality. If you treated a guest or stranger badly, you could outrage Zeus and not be treated so favorably (Figure 3-2).
Because lightning was a manifestation of the gods, any spot struck by lightning was regarded as sacred. Temples often were erected at these sites, where the gods were worshipped in an attempt to appease them.
Roman mythology saw lightning as more ominous than did the Greeks, with Jupiter using thunderbolts as tools of vengeance and condemnation. Romans killed by lightning strikes were considered damned by Jupiter and denied burial rituals. Several Roman emperors wore laurel wreaths or sealskin to ward off lightning strikes. Important matters of state were often decided on observations of lightning and other natural phenomena. Both Seneca and Titus Lucretius discussed lightning in their treatises on natural events, and Plutarch noted that sleeping persons, having no spirit of life, were immune to lightning strikes.
The Navajo Indians of North America have a story about the hero Twins who used “the lightning that strikes straight” and “the lightning that strikes crooked” to kill several mythic beasts that were plaguing the People (Navajo) and in the process created the Grand Canyon.
Bantu tribesmen in Africa believed that lightning was due to the flashing feathers of a mystic bird whose flapping wings produced the sound of thunder. Umpundulo is the name of the lightning bird-god (Figure 3-3, online). They hold that lightning has great power in their healing rituals. Even today, their medicine men go out in storms and bid lightning to strike far away. Sand paintings show the lightning bolt as a wink in the thunderbird’s eye. Lightning is associated with wind, rain, and crop growth.
The art of native Australians incorporates lightning symbols, where the lightning spirit is depicted as having axes, attached to his joints, that beat together to make thunder.
Lightning also played a role in Buddhist symbolism. Early statues of Buddha show him carrying a thunderbolt with arrows at each end. Although lightning is most frequently rendered as fire, it has also been represented as stone axes hurled from the heavens. In the pantheistic Hindu religion, Indra (Figure 3-4, online) was the god of heaven, lightning, rain, storms, and thunder. The Maruts used thunderbolts as weapons.
The Yakuts of eastern Asia regard rounded stones found in fields hit by lightning as thunder axes and often use the powdered stones in medicines and potions. In Chinese mythology, the goddess of lightning, Tien Mu, used mirrors to direct bolts of lightning. She was one of the deities of the “Ministry of Thunderstorms” of ancient Chinese religion.
Scandinavian mythology alludes to Thor (Figure 3-5, online), the thunderer, who was the foe of all demons. Thor tossed lightning bolts at his enemies, and Thursday is named for him. For the Vikings, lightning was produced by Thor as his hammer struck an anvil while riding his chariot across the clouds.
Throughout early Europe, church bell ringers would make as much noise as possible, hoping to scare away the storms from holy dwellings whose steeples were struck frequently by lightning. French peasants carry a pierre de tonnerre, or lightning stone, to ward off lightning strikes. Even Santa Claus gets into the act with his reindeer Donner (thunder) and Blitzen (lightning).
People in both developed and Third World countries often regard lightning and thunder with a great deal of fear as mysterious, uncontrollable, and unmanageable. Cambodians, for instance, believe that by doing good deeds, they can avoid lightning strikes and that people with moles on their calves are susceptible to lightning strikes, as are people who have broken promises. To resuscitate a victim, Cambodian villagers may drape the person’s body with a white cloth, or jump over it three times, or place the victim in a bed and light a fire under the bed.
In South Africa, there is a belief that lightning can be “sent” to steal something, or from a traditional healer to someone else. In the Venda and Tsonga cultures of South Africa, families may petrol bomb the house of an enemy who they believed called down lightning on a relative who was struck. In Africa in the 1990s, when only the members of one soccer team were injured, it was ascribed to witchcraft on the part of the other team. Other African beliefs state that burying a hippopotamus hide 2.4 m (8 feet) under ground will protect their area. Wearing red is believed to be protective, but mirrors are felt to attract lightning, not only in Africa but in other cultures, including the United States.
South Africans believe that the Syringa tree (Figure 3-6, online) attracts lightning. So strong is this belief that some farmers will cut down every Syringa tree on their farm.
FIGURE 3-6 So strong is the belief among South Africans that the Syringa tree attracts lightning that farmers will cut down every Syringa tree on their farms.
Even in “civilized” Western societies, lightning can take on mystical significance. When lightning struck an English cathedral just before enthronement of a controversial bishop in the late 20th century, some regarded it as an omen. Bullock,35,36 in a modern article, advances a case that the conversion of Saul on the road to Damascus was a result of a lightning strike.
Common Modern Myths, Superstitions, and Misconceptions*
The Roman author Pliny noted that a man who heard thunder was safe from the lightning stroke. This implies that the person who hears the thunder is far enough away from the lightning strike to survive it, although today we know the person may still be injured. Persons so close that they cannot hear the thunder are much more likely to be injured. Persons who receive ground current are more likely to report both seeing the flash and hearing the stroke, indicating that the main stroke was some distance away.
Many myths about lightning, including the notion that lightning strikes are invariably fatal, persist (Box 3-1). According to an American study of cases reported in the lightning literature since 1900, lightning strike carries a mortality rate of 30% and a morbidity rate of 70%.64 A slightly different statistical interpretation of the same data yielded a mortality figure of 20%.18 Because literature reports are usually biased toward severe or interesting cases, case reviews tend to overestimate mortality rate. In reality, mortality rate may be as low as 5% to 10%.54
BOX 3-1 The Most Common Myths and Facts
Most people suspect that the major cause of death is from burns. However, the only cause of immediate death is from cardiac arrest.64 Persons who are stunned or lose consciousness without cardiopulmonary arrest are highly unlikely to die, although they may still have serious and long-term sequelae.67,74,212,232 Delayed causes of death include suicide induced by depression and disability wrought by lightning.67
Most people “have enough sense to come out of the rain” and seek shelter when storm clouds roll overhead. Unfortunately, a large number of injuries occur as the storm is approaching because people misjudge it, do not pay attention to warning signs, or want to finish one more thing before seeking shelter.66,135 Lightning may travel nearly horizontally as far as 10 miles or more in nearly any direction from a thunderstorm and seem to occur “out of a clear blue sky,” or at least when the day is still sunny where the person is located. At least 10% of cloud-to-ground strikes occur when no rain is occurring at the time and location of the strike. The faster the storm is traveling and the more violent it is, the more likely a fatal strike will occur. Another dangerous time is at the end of a thunderstorm, when people go out to begin activities before the danger has passed. Lightning casualties have decreased dramatically in the last few decades,138,143,217 but people continue to be injured when they could easily be in safe shelters only a few feet away from where they were hit.
“When thunder roars, go indoors” is the teaching mantra of the National Weather Service’s (NWS’s) Lightning Awareness Week for individuals and small groups (www.lightningsafety.noaa.gov).217 Although one might suppose seeing lightning is a reliable warning, this is not always the case. On the great plains of the United States, lightning may be seen up to one-hundred miles away, but in the woods of Maine, it may not be seen at all before people are in danger. Thus, seeing lightning is too variable to use reliably because it may overestimate or underestimate the risk. Thunder is a much more reliable tool for estimating distance and danger, because it is seldom audible more than 10 miles away. Unfortunately, in special cases, such as in a city, heavy traffic areas, or a noisy sports stadium, it may be less audible.
The flash-to-bang method is now used less often than it was a decade ago, because of uncertainty in linking flashes to thunder, as well as confusion in how to calculate the distance. The “30-30 rule,” a modification of the flash-to-bang method, was adopted in the mid-1990s as a catchy teaching tool.27,217 The first 30 stood for counting the seconds from seeing lightning to hearing its thunder at the beginning of a storm. If the count was 30 or less, the person was in danger and should be seeking safer shelter. It soon became apparent that the recommendation should be that the person actually be in safe shelter at that point. This part of the rule was replaced by “When thunder roars, go indoors.”217 The second 30 is still useful and indicates the number of minutes at the end of the storm after seeing the last lightning or hearing the last thunder that one should wait before once again going outside and resuming activity. Although the “30-30 rule” has been abandoned for individuals, it is useful for some larger venues such as industrial sites.216,217
One of the most dangerous and consistent places of injury is standing near a tree or other tall object. Tent poles, regardless of their construction, can be a source of lightning injury. Standing in an isolated flat area (larger than 15 to 30 m [49 to 98 feet] in diameter) is a recipe for disaster.
Lighting injuries may occasionally occur indoors, particularly from contact injury or side flashes from plumbing fixtures, computers, hard-wired telephones or electronic game devices, and other appliances.8,95,96 With a hard-wired phone, persons may suffer acoustic damage,17,209 neurocognitive deficits, death, or other lightning-related problems, because the phone system in most houses is not grounded to the house’s electrical system and so acts as a conduit for lightning either to come into the home or to exit from it. Cell phones, on the other hand, offer complete protection from the indoor electrical effects.*
Because of the nearly universal use of cell phones, more injuries have been reported to people using them. It has been mistakenly concluded that they “attract” lightning (Figure 3-7, online). However, injury occurs because mobile phones, iPods, and similar devices distract people from paying attention to the weather, as well as other dangers, when they are outside, delaying them from seeking safe shelter, not because the devices have any effect on thunderstorms or lightning.†
Although small sheds, such as hikers’ lean-tos, or sun, rain, bus, or golf shelters, may be protected or “hardened” against lightning strike under the National Fire Protection Association (NFPA) lightning codes (NFPA780), this is no guarantee of safety to persons sheltering within them.171,215,216 Personal safety is not guaranteed by structural protection. Grounding of the building is no guarantee of safety. In fact, it is likely that using these shelters can actually increase a person’s risk for injury for reasons including side flash and ground current. One should think of these shelters as capacitors with air insulation between the capacitor plates (roof and the floor). It is easy to see why someone standing inside decreases the amount of energy needed to “discharge” the capacitor and send lightning energy through the person. Similarly, sheltering within a shallow cave on a mountainside may protect from rain but may be very dangerous from a lightning standpoint.
The “crispy critter” myth is the belief that someone struck by lightning bursts into flames or is reduced to a pile of ashes.59 In reality, lightning often flashes over the outside of a victim, sometimes blowing off the clothes but leaving few external signs of injury and few, if any, burns. Less than one-third of lightning survivors have any signs of burns or marks to their skin.
Two other myths held by the public and many physicians are that “If you’re not killed by lightning, you’ll be OK” and “If there are no outward signs of lightning injury, the damage can’t be serious” (Box 3-2).66 Medical literature, because of lack of follow-up or longitudinal reports, implies that there are few permanent sequelae of lightning injury. Several permanent sequelae may occur.* In addition, many lightning victims with significant sequelae have no evidence acutely of burns. Peripheral neuropathy, chronic pain syndromes, and neuropsychological symptoms, including severe short-term memory difficulty, difficulty processing new information, attention deficit, depression, and post-traumatic stress disorder, may be debilitating.221,229–233,235,237
BOX 3-2 Myths Commonly Cited as Facts in Litigation
These apply to electrical injury as well as lightning injury.
Behavior of Current in the Body
The Severity of Electric Shock
Myth: If the following are absent, the shock cannot be severe and no deleterious effect can result:
A myth still prevalent is that the lightning victim retains the charge and is dangerous to touch because he or she is still “electrified.” A person does not retain a charge like a battery. This myth has led to unnecessary deaths by delayed resuscitation efforts.66
Medical literature and practice are plagued by myths that grew out of misread, misquoted, or misinterpreted data and continue to be propagated without further investigation. Not the least of these is the tenet that lightning victims who have resuscitation for several hours may still successfully recover. This belief seems to be grounded in the old idea of suspended animation—the concept that lightning is capable of shutting off systemic and cerebral metabolism, allowing rescuers a longer period in which to resuscitate the patient without anoxic injury. This concept, credited to Taussig,266 actually appeared some time before her article. In addition, the case recounted by Taussig that is the basis for this myth, when searched to its source, was a case report by Morikawa and Steichen.210 The case shows a somewhat longer resuscitation period than usual, but not as miraculous as reported in Taussig’s paper or as propagated in subsequent references to her paper.
In a study of lightning survivors, Andrews, Colquhoun, and Darveniza13 have shown prolongation of the QT interval, bringing up the theoretic possibility of torsades de pointes as a mechanism for the suspended animation reports. There is evidence from animal experiments to support the teaching that respiratory arrest may persist longer than does cardiac arrest.9,80,81 One study, in which Australian sheep were hit with simulated lightning strokes, showed histologic evidence of damage to the respiratory centers located beneath the fourth ventricle.9 Prolonged assisted ventilation may in some cases be successful after cardiac activity has returned, but this is obviously difficult to test in any clinical study.69,70,225
Another series of animal experiments with hairless rats has shown that it is possible to obtain the skin changes (keraunographic markings), primary and secondary cardiac arrest with prolonged respiratory arrest, and temporary lower extremity paralysis with simulated lightning strike.80,81
Several booklets listing precautions for personal lightning protection appeared in the late 1700s and early 1800s. One of the superstitions listed was that humans, by their presence, could attract lightning to a nearby object. A book of the times, Catechism of Thunderstorms, illustrated other myths. Lightning was said to follow the draft of warm air behind a horse-drawn cart, so that coachmen were cautioned to walk their horses slowly through a storm.
Historically, many remedies for resuscitation of lightning victims have been offered. On July 15, 1889, Alfred West testified in a New York court that he was revived by “drawing out the electricity” when his feet were placed in warm water while his rescuer pulled on Mr. West’s toes with one hand and milked a cow with the other.29
Other early attempts at resuscitation included friction to bare skin, dousing the victim with a bucket of cold water, and chest compression. An early attempt at cardiopulmonary resuscitation was given in 1807 when mouth-to-mouth ventilation was used for lightning victims, and it was proposed that gentle electric shocks from galvanic batteries passed through the chest might be successful in resuscitating a victim of lightning.40 Before that, Benjamin Franklin110 had purposely electrocuted a chicken during a lightning experiment and reported successful, albeit temporary, resuscitation with mouth-to-beak ventilation.
A myth in current treatment is that lightning injuries should be treated like other high-voltage electrical injuries. The injuries seen with lightning are very different from high-voltage injuries and should be treated differently if iatrogenic morbidity and mortality are to be avoided.15,65
“Lightning never strikes the same place twice.” In reality, the Empire State Building and the Willis Tower are hit dozens of times a year, as are mountaintops and radio-television towers. If the circumstances facilitating the original lightning strike are still in effect in an area, the laws of nature will encourage further lightning strikes.
FIGURE 3-8 Simulated lightning in a high-voltage laboratory travels across the external metal body of the car, escaping through the axle, hubcaps, or other metal closer to ground (arrow). The Faraday cage effect of the metal body of the car protects the person from injury but does not protect the tires or wiring system of the vehicle.
Metal objects, such as fences and bleachers, conduct electricity and lightning after they have been hit, but they do not attract lightning. Metal objects worn by the victim may heat and cause secondary injury but do nothing to attract lightning. Tall objects tend to be made of metal, but their height, isolation, and pointiness, not their composition, are factors.
Incidence of Injury
Lightning Across the United States
The distribution of lightning across the United States is well known because of the operation of real-time lightning detection networks for the past two decades.86,94 About 25 million cloud-to-ground flashes occur each year in the lower 48 states.226 In addition to the strike points of the first return strokes, 45% of flashes have a subsequent return stroke that terminates at a different location on the ground.271 As a result, about 37 million ground terminations are directly impacted by cloud-to-ground lightning over the United States each year. The variability from year to year over the entire country is only a few percent due to the compensating effects of a variety of meteorologic regimes over the course of a year. On a shorter time scale, more than 50,000 flashes per hour sometimes occur on summer afternoons across the United States. Existing technology detects over 90% of all cloud-to-ground flashes within the contiguous United States.86
The most recent 11-year climatology of cloud-to-ground lightning from the National Lightning Detection Network shows that three locations along the east and west coasts of peninsular Florida have the largest density of flashes per area during the entire year (Figure 3-9). Flash density decreases northward and westward from Florida, although there are many variations that depend on the well-identified meteorologic factors of strongly heated land surfaces producing strong upward motions in the atmosphere because of coastal sea breezes during most summer afternoons. This acts on deep moisture in the lower levels of the atmosphere. Similar important features occur along the coast of the Gulf of Mexico. In the mountainous western states, strong upward atmospheric motions are produced during many summer days along with large changes in elevation.194
Lightning Around the World
Over 60 cloud-to-ground lightning detection systems using commercial instrumentation in the very low frequency (VLF) and low frequency (LF) range have been installed in more than 45 countries on every continent except Antarctica.86 Some have operated for longer than two decades. However, the only formally published compilation of flash data from more than one country at a time is for the United States and Canada.226
The ability to detect the full horizontal and sometimes vertical extent of flashes in cloud has been developed in recent years.86,193 These cloud lightning or total lightning flashes are detected in the VHF range over regions as large as metropolitan areas. Total lightning networks detect three to five cloud flashes for every cloud-to-ground flash, although some storms have much higher ratios. The longest detected cloud flash stretched horizontally across 190 km (118 miles) over the Dallas-Fort Worth area and was connected with two cloud-to-ground flashes during its 2-second lifetime.92
Cloud flashes do not directly affect people on the ground. However, their association with cloud-to-ground flashes helps to understand the location and timing of ground strikes. No maps of total lightning have been developed to date, although there is a general view of worldwide total lightning detected by the satellite-borne Optical Transient Detector and Lightning Imaging Sensor that measure both cloud-to-ground and cloud flashes as shown in Figure 3-10.59
FIGURE 3-10 Total flashes per square kilometer per year for the world from April 12, 1995, to December 31, 1999 from the Optical Transient Detector.
The highest rates of all types of lightning occur over tropical and subtropical continents. Maxima have been found in central Africa and northwest South America.2 Lightning frequencies in these areas far exceed those over Florida and the Gulf Coast. The uncertainty concerning the portion of these maxima that are cloud-to-ground flashes is being resolved by the recent deployment of the Global Lightning Dataset GLD360.93
Time of U.S. Lightning*
During the year, lightning is by far most common during summer months. Two-thirds of U.S. cloud-to-ground flashes occur in June, July, and August (Figure 3-11, online). The maximum during the warmer months of the year, especially in the southeastern states, is due primarily to daytime heating of the lower and middle levels of the atmosphere. An equally critical ingredient is the large amount of moisture in the lower and middle levels of the atmosphere that provides fuel for the daily thunderstorm cycle. The concentration of U.S. cloud-to-ground lightning in June, July, and August is present over nearly all of the United States.141
FIGURE 3-11 Cloud-to-ground flashes per month from 2004 to 2008 for the United States from the National Lightning Detection Network.
(Courtesy Vaisala, Inc, Tucson, Ariz.)
During the day, cloud-to-ground lightning is most common in the afternoon (Figure 3-12, online). Nearly one-half of all lightning occurs between noon and 18:00 local standard time (LST). Lightning is at a maximum in the afternoon because updrafts necessary for thunderstorm formation are strongest during the warmest times of the day when surface temperatures are highest, resulting in the greatest vertical instability. Other factors can extend the maximum into the evening hours, especially in the plains and southeastern states, because of outflows and other propagating features that usually originate with the afternoon convection.
U.S. Lightning Casualties
Each month, NWS offices compile a list of damaging or notable weather phenomena that occurred in the office’s area of responsibility. These lists are combined into a monthly national report issued by the National Oceanic and Atmospheric Administration (NOAA) titled Storm Data.
During the last 20 years, U.S. lightning fatalities have averaged 51 per year. Lightning deaths have equaled or exceeded those from tornadoes in 11 years and equaled or exceeded those from hurricanes in 18 of the 20 years (Figure 3-13). Flood deaths exceeded lightning fatalities during 16 of these 20 years.
FIGURE 3-13 U.S. storm-related fatalities from 1989 through 2008 from the National Oceanic and Atmospheric Administration publication Storm Data. The sign indicates that hurricane Katrina had 1016 fatalities in 2005.
Males (84%) make up a much higher number of fatalities in the United States than females.87 This male majority has been found in every region of the world over the last two centuries, although some subsets can have less dominance of males than this typical value.
The most common situation is for one victim to be involved in a lightning incident. The largest single death total in one U.S. event resulted from a 1963 airliner crash that killed 81, and the largest U.S. injury total was 90 at a Michigan campground. Although single-incident cases dominate the more developed countries’ data sets, very large numbers of deaths and injuries often occur in developing countries.140
Lightning-related casualties and damages are often less spectacular and more dispersed in time and space than are those from other storm phenomena. As a result, lightning deaths, injuries, and damages have been found to be underreported in Storm Data.19,144,196,258 The following factors contribute to this underreporting: most casualties occur to one person or object at a time, Storm Data collection is not entirely consistent among offices, there are some differences in the definitions of lightning versus secondary lightning-related deaths, and there is inconsistency in listing medical diagnoses.1,19,239,258
Nonfatal injuries are underreported to a greater extent than are fatalities. A thorough search of Colorado hospital and emergency department visits found a ratio of 10 injuries to every death.53 Although this ratio of injuries to fatalities is generally applicable, there may be additional injuries that are not reported.
Damage reports in Storm Data are an extremely small portion of the estimated total damages, direct or indirect, of several billion dollars per year in the United States.19,144 Despite its underreporting and sometimes incomplete nature, Storm Data has been a consistent national database for lightning impacts since 1959 and is likely the best system in the world for such information.
Data drive change. It would be highly desirable for similar data to be collected and made available in many other areas of the world, both to have a baseline of damage and injuries to measure changes and to spur governments and other organizations to address injury prevention.
Distribution of U.S. Lightning Deaths by State
Lightning casualty deaths in the United States by state for the decade from 1999 to 2009 are shown in Figures 3-14 and 3-15. The general pattern is somewhat similar to the distribution of lightning in Figure 3-9. In general, there are more fatalities in the Southeast, but the more populous states also have larger totals. Note that Florida has had more than twice as many deaths as Colorado, the next state in terms of frequency. Fatality information is used for these maps, rather than injuries, because of the greater uncertainty due to injury underreporting, as mentioned previously.
FIGURE 3-14 Rank and number of lightning fatalities in each state from 2000 to 2009 from Storm Data.
(Modified from Curran EB, Holle RL, López RE: Lightning casualties and damages in the United States from 1959 to 1994, J Climate 13:3448, 2000.)
FIGURE 3-15 Rank of population-weighted lightning fatality rate in each state from 2000 to 2009 from Storm Data.
(Modified from Curran EB, Holle RL, López RE: Lightning casualties and damages in the United States from 1959 to 1994, J Climate 13:3448, 2000.)
The lightning hazard is shown more clearly when population is taken into account in Figure 3-15. There are two maxima with this approach, one in the southeast and the other in the northern Rocky Mountain states. Most populous states, such as Illinois, no longer have high ranks. The only states in the top 10 of both lightning fatality and fatality rates are Florida, Colorado, Alabama, and South Carolina.
Similar tabulations were recently made by Ashley and Gilson,19 and earlier maps for single U.S. states are listed by Curran and colleagues.87 Outside the United States, the distributions of fatalities by political boundaries have been developed for Canada,207 Singapore,228 Australia,61 and France.116 Many additional studies have included national casualty totals, but not maps, over periods from several to many years.138
Time of U.S. Fatalities
During the course of the year, lightning fatalities are nearly symmetric around the most frequent month of July (Figure 3-16, online). This annual casualty cycle is quite similar to the cloud-to-ground lightning variation by month in Figure 3-11, online. Because summer dominates the sample size, summer fatality maps are very similar to Figures 3-11 and 3-12, online for the entire year.87 On the West Coast, fatality rates are highest during autumn and winter, and these rates are also higher in the southern states than elsewhere in months other than summer. Outside the United States and away from the tropics, summer also accounts for the largest number of fatalities, such as that shown by the January peak in Australia because of the reversal of seasons from the northern hemisphere.61 In the equatorial location of Singapore, fatality maxima in November and April are similar to the annual maxima in local thunderstorms.228
FIGURE 3-16 Lightning fatalities per month from 1959 to 1994 for the United States.
(From Curran EB, Holle RL, López RE: Lightning casualties and damages in the United States from 1959 to 1994, J Climate 13:3448, 2000.)
During the hours of the day, most lightning fatalities occur during the afternoon (Figure 3-17, online). About two-thirds of U.S. fatalities occur between noon and 18:00 LST.87 There is a somewhat faster rise up to the maximum then a slower decrease afterward. This general cycle is very similar to cloud-to-ground lightning in Figure 3-12, online. However, there is a somewhat narrower concentration of fatalities in the afternoon in the Rockies, southeast, and northeast compared with the broader time series in the plains and Midwest.87 At night between 18:00 and 06:00, the relatively few fatalities occur mostly in the plains, upper Midwest and some populous eastern states, because of outflows and other propagating features that usually begin with afternoon convection. More than one-half of the deaths after midnight occurred when people were in a house set on fire by lightning,139 whereas some fatalities were campers.
Trends in U.S. Lightning Fatalities
During the early years of the 20th century, U.S. lightning deaths were much more frequent than at present (Figure 3-18). Not all states participated in lightning fatality data collection systems in the early years of the period shown in Figure 3-18. However, once all states reported, the peak was reached in 1921, when 459 lightning fatalities were reported.195 Since then, there has been a steady decline in the number of fatalities listed in Storm Data. In recent years, there have been less than 50 fatalities annually.
FIGURE 3-18 Annual reported U.S. lightning fatalities from 1900 to 2007.
(Modified from López RE, Holle RL: Changes in the number of lightning deaths in the United States during the twentieth century, J Climate 11:2070, 1998.)
The steady downward trend is made more noticeable by population weighting, shown in Figure 3-19. Although the U.S. population has increased greatly since 1900, the weighted rate has decreased from as high as 6 fatalities per million people per year in the early 20th century to about 0.3 in recent years. Paralleling this decrease is a shift from a mainly rural to a mostly urban population in the United States during the same years (see Figure 3-19). Other significant factors that contribute to this downward trend are improved grounding of home and building electrical and plumbing systems, ready access to fully enclosed metal-topped vehicles, improved medical treatment, and greater meteorologic and lightning awareness and warnings. The potential effects of changing fatality data collection rules and methods are difficult to identify but may account for some variations in all data sets.
FIGURE 3-19 Annual lightning fatalities weighted by population () from 1900 to 2007 for the United States and rural percentage ().
(Modified from López RE, Holle RL: Changes in the number of lightning deaths in the United States during the twentieth century, J Climate 11:2070, 1998.)
The net effect of these changes is apparent in a comparison of fatality data from the 1890s to 1990s in Figure 3-20.195 Agricultural cases have decreased from 26% to 10%, while indoor cases went from 40% to 5%. The latter may be due to the introduction of grounding into buildings, often on a farm or ranch, which has greatly reduced the lighting threat in recent years. There has been a large increase in recreational and sports incidents during that century and in the general category of outdoors, often in the yard of a dwelling and other everyday situations.
Worldwide Lightning Fatalities
The weighted U.S. lightning fatality rate dropped during the 20th century by more than a factor of 10, from 6 deaths per million in some early years to under 0.3 in most recent years, as shown in Figure 3-19. Three apparently dominant factors are reduction in the rural population involved in labor-intensive agriculture, substantial grounding of most buildings where people live and work, and ready availability of fully enclosed metal-topped vehicles. Other more developed countries, such as Australia, Canada, England and Wales, France, Japan, and Sweden, have seen very similar reductions. All show current rates of less than 0.5, although some had rates exceeding 2 a century ago in areas where the lightning frequency is not as high as in the United States.138
Many people continue to participate in labor-intensive agriculture and live in ungrounded buildings in areas of the world where lightning frequency is high.163,164 The rates a century ago in the United States and other more developed countries can be considered for estimating fatalities and injuries in locations where lightning injury statistics are not readily available. Populous regions of Africa, South America, and Southeast Asia have as many as 4 billion people who are vulnerable to the lightning threat, although urbanization makes it difficult to know the number of agriculturally dependent people living in unsafe structures. If the annual rate of 6 fatalities per million is used for 4 billion people, a total of 24,000 lightning deaths per year is obtained. If there are 10 injuries for every death,54 then 240,000 injuries occur per year in these areas. Holle138 lists all known published estimates of the lightning totals and converts them to fatality rates per population. Some of the countries indeed reach the rate of 6 per million per year, whereas other less developed countries have much lower rates (Figure 3-21).
FIGURE 3-21 Lightning deaths per million people per year for eight countries outside Europe by decade during the 20th century. Note that the 1990s Zimbabwe value is 17.8.
(From Holle RL: Annual rates of lightning fatalities by country. Preprints, International lightning detection conference, April 21-23, 2008, Tucson, Ariz., Vaisala.).