Lightning strike

A lightning strike or lightning bolt is an electric discharge 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 69% of all lightning events worldwide are strikes between the atmosphere and earth-bound objects. Most are intra-cloud (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.
A single lightning event is a "flash", which is a complex, multi-stage process, some parts of which are not fully understood. Most CG flashes only "strike" one physical location, referred to as a "termination". The primary conducting channel, the bright coursing light that may be seen and is called a "strike", is only about one inch in diameter, but because of its extreme brilliance, it often looks much larger to the human eye and in photographs. Lightning discharges are typically miles long, but certain types of horizontal discharges can be upwards of tens of miles in length. The entire flash lasts only a fraction of a second.
Strikes.
Lightning strikes can injure humans in several different ways:
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 have to be touching).
Injuries.
Lightning strikes can produce severe injuries, 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.
In a direct strike, the electrical currents in the flash channel passes directly through the victim. The relatively high voltage drop around poorer electrical conductors (such as a human being), causes the surrounding air to ionize and break down, and the external flashover diverts most of the main discharge current so that it passes "around" the body, reducing injury.
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.
However, during a flash, the current flowing through the channel and around the body will 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.
Another effect of lightning on bystanders is to their hearing. The resulting shock wave of thunder can damage the ears. Also, electrical interference to telephones or headphones may result in damaging acoustic noise.
Epidemiology.
About 240,000 incidents regarding lightning strikes happen globally each year.
According to National Geographic, annually about 2,000 people are killed worldwide by lightning. Therefore, the average human being, according to these figures has roughly a 1 in 60,000 to 80,000 chance of falling victim to lightning in an average lifetime (of about 65–70 years). Furthermore, due to increased awareness and improved lightning conductors and protection, the number of annual lightning deaths has been decreasing steadily year by year.
According to the NOAA, over the last 40 years, the United States averaged 51 annual lightning strike fatalities, placing it in the second position, just behind floods for deadly weather. In the US, between 9% and 10% of those struck die, with an annual average of 25 deaths in the 2010s decade (16 in 2017).
In Kisii in western 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.
These statistics do not reflect the difference between direct strikes, where the victim was part of the lightning pathway, indirect effects of being close to the termination point, like ground currents, and resultant, where the casualty arose from subsequent events, such as fires or explosions. Even the most knowledgeable first responders may not recognize a lightning-related injury, let alone particulars, which a medical examiner, police investigator or on the rare occasion a trained lightning expert may have difficulty identifying to record accurately. This ignores the reality that lightning, as the first event, may assume responsibility for the overall and resulting accident.
Direct strike casualties could be much higher than reported numbers.
Effect on nature.
Impact on vegetation.
Trees are frequent conductors of lightning to the ground. Since sap is a relatively poor conductor, its electrical resistance causes it to be heated explosively into steam, which blows off the bark outside the lightning's path. In following seasons trees overgrow the damaged area and may cover it completely, leaving only a vertical scar. If the damage is severe, the tree may not be able to recover, and decay sets in, eventually killing the tree.
In sparsely populated areas such as the Russian Far East and Siberia, lightning strikes are one of the major causes of forest fires. The smoke and mist expelled by a very large forest fire can cause electric charges, starting additional fires many kilometers downwind.
Shattering of rocks.
When water in fractured rock is rapidly heated by a lightning strike, the resulting steam explosion can cause rock disintegration and shift boulders. It may be a significant factor in erosion of tropical and subtropical mountains that have never been glaciated. Evidence of lightning strikes includes erratic magnetic fields.
Electrical and structural damage.
Telephones, modems, computers and other electronic devices can be damaged by lightning, as harmful overcurrent can reach them through the phone jack, Ethernet cable, or electricity outlet. Close strikes can also generate electromagnetic pulses (EMPs) – especially during "positive" lightning discharges.
Lightning currents have a very fast rise time, on the order of 40 kA per microsecond. Hence, conductors of such currents exhibit marked skin effect, causing most of the currents to flow through the outer surface of the conductor.
In addition to electrical wiring damage, the other types of possible damage to consider include structural, fire, and property damage.
Prevention and mitigations.
The field of lightning protection systems is an enormous industry worldwide due to the impacts lightning can have on the constructs and activities of humankind. Lightning, as varied in properties measured across orders of magnitude as it is, can cause direct effects or have secondary impacts; lead to the complete destruction of a facility or process or simply cause the failure of a remote electronic sensor; it can result in outdoor activities being halted for safety concerns to employees as a thunderstorm nears an area and until it has sufficiently passed; it can ignite volatile commodities stored in large quantities or interfere with the normal operation of a piece of equipment at critical periods of time.
Most lightning protection devices and systems protect physical structures on the earth, aircraft in flight being the notable exception. While some attention has been paid to attempting to control lightning in the atmosphere, all attempts proved extremely limited in success. Chaff and silver iodide crystal concepts were devised to deal directly with the cloud cells and were dispensed directly into the clouds from an overflying aircraft. The chaff was devised to deal with the electrical manifestations of the storm from within, while the silver iodide salting technique was devised to deal with the mechanical forces of the storm.
Lightning protection systems.
Hundreds of devices, including lightning rods and charge transfer systems, are used to mitigate lightning damage and influence the path of a lightning flash.
A lightning rod (or lightning protector) is a metal strip or rod connected to earth through conductors and a grounding system, used to provide a preferred pathway to ground if lightning terminates on a structure. The class of these products are often called a "finial" or "air terminal". A lightning rod or "Franklin rod" in honor of its famous inventor, Benjamin Franklin, is simply a metal rod, and without being connected to the lightning protection system, as was sometimes the case in the old days, will provide no added protection to a structure. Other names include "lightning conductor", "arrester", and "discharger"; however, over the years these names have been incorporated into other products or industries with a stake in lightning protection. Lightning arrester, for example, often refers to fused links that explode when a strike occurs to a high voltage overhead power line to protect the more expensive transformers down the line by opening the circuit. In reality, it was an early form of a heavy duty surge protection device (SPD). Modern arresters, constructed with metal oxides, are capable of safely shunting abnormally high voltage surges to ground while preventing normal system voltages from being shorted to ground.
In 1962, the USAF placed protective lightning strike-diversion tower arrays at all of the Italian and Turkish Jupiter MRBM nuclear armed missiles sites after two strikes partially arming the missiles.
Monitoring and warning systems.
The exact location of a lightning strike or when it will occur is still impossible to predict. However, products and systems have been designed of varying complexities to alert people as the probability of a strike increases above a set level determined by a risk assessment for the location's conditions and circumstances. One significant improvement has been in the area of detection of flashes through both ground and satellite-based observation devices. The strikes and atmospheric flashes are not predicted, however the level of detail recorded by these technologies has vastly improved in the past 20 years.
Although commonly associated with thunderstorms at close range, lightning strikes can occur on a day that seems devoid of clouds. This occurrence is known as "A Bolt From the Blue"; lightning can strike up to 10 miles from a cloud.
Lightning interferes with AM (amplitude modulation) radio signals much more than FM (frequency modulation) signals, providing an easy way to gauge local lightning strike intensity. To do so, one should tune a standard AM medium wave receiver to a frequency with no transmitting stations, and listen for crackles amongst the static. Stronger or nearby lightning strikes will also cause cracking if the receiver is tuned to a station. As lower frequencies propagate further along the ground than higher ones, the lower medium wave (MW) band frequencies (in the 500–600 kHz range) can detect lightning strikes at longer distances; if the longwave band (153–279 kHz) is available, using it can increase this range even further.
Lightning detection systems have been developed and may be deployed in locations where lightning strikes present special risks, such as public parks. Such systems are designed to detect the conditions which are believed to favor lightning strikes and provide a warning to those in the vicinity to allow them to take appropriate cover.
Personal safety.
The U.S. National Lightning Safety Institute advises American citizens to have a plan for their safety when a thunderstorm occurs and to commence it as soon as the first lightning is seen or thunder heard. This is important as lightning can strike without rain actually falling. If thunder can be heard at all, then there is a risk of lightning. The safest place is inside a building or a vehicle. Risk remains for up to 30 minutes after the last observed lightning or thunder.
The National Lightning Safety Institute recommends using the F-B (flash to boom) method to gauge distance to a lightning strike. The flash of a lightning strike and resulting thunder occur at roughly the same time. But light travels 300,000 kilometers in a second, almost a million times the speed of sound. Sound travels at the slower speed of about 340 m/s (depending on the temperature), so the flash of lightning is seen before thunder is heard. A method to determine the distance between lightning strike and viewer, involves counting the seconds between the lightning flash and thunder. Then, dividing by three to determine the distance in kilometers, or by five for miles. Immediate precautions against lightning should be taken if the F-B time is 25 seconds or less, that is, if the lightning is closer than 8 km or 5 miles.
A report suggested that it did not matter whether a person was standing up, squatting, or lying down when outside during a thunderstorm, because lightning can travel along the ground; this report suggested it was safest to be inside a solid structure or vehicle. In the United States, the average annual death toll from lightning is around 51 deaths per year, although more recently, in the period 2009 to 2018, the U.S. has averaged only 27 lightning fatalities per year. The riskiest activities include fishing, boating, camping, and golf. A person injured by lightning does not carry an electrical charge, and can be safely handled to apply first aid before emergency services arrive. Lightning can affect the brainstem, which controls breathing.
Several studies conducted in South Asia and Africa suggest that the dangers of lightning are not taken sufficiently seriously there. A research team from the University of Colombo found that even in neighborhoods which had experienced deaths from lightning, no precautions were taken against future storms. An expert forum convened in 2007 to address how to raise awareness of lightning and improve lightning protection standards, and expressed concern that many countries had no official standards for the installation of lightning rods.
Notable incidents.
All events associated or suspected of causing damage are called "lightning incidents" due to four important factors.
As such it is often inconclusive, albeit highly probably a lightning flash was involved, hence categorizing it as a "lightning incident" covers all bases.
In-flight.
Airplanes are commonly struck by lightning without damage, with the typical commercial aircraft hit at least once a year. However, sometimes the effects of a strike are serious. 