A lightning strike or lightning is the electrical discharge between the atmosphere and the object that is bound to the Earth. They mostly come from cumulonimbus clouds and end up on the ground, called cloud to ground (CG). The less common strike type, called ground to cloud (GC), is an upward jet that starts from a high object and reaches to the cloud. About 25% of all lightning events worldwide occur between the atmosphere and the objects that are bound to the earth. Most of the lightning events are intra-cloud (IC) or cloud to cloud (CC), where discharges only occur high in the atmosphere.
One flash event is "flash", which is a complex multi-stage process, some parts are not fully understood. Most cloud to ground blinks just "attack" a physical location, called "termination". The main conductor channel, visible light, called a "strike", is only about an inch in diameter, but because of its extreme brilliance, it often looks much bigger on the human eye and photographs. Lightning discharges are usually miles and miles long, but certain horizontal disposal types can reach tens of miles. The whole flash lasts only a fraction of a second. Most of the early formative and propagation stages are much more dim and invisible to the human eye.
Video Lightning strike
Strikes
Lightning strikes can injure people in several different ways:
- Direct
- Direct rebuke - the person is part of the channel flash. A large amount of energy passes through the body very quickly and this can lead to internal burns and organ damage, flesh and bone explosions, and damaged nervous system. Depending on the strength of the flash and access to medical services, it can instantly be fatal or cause permanent injury and interference.
- Contact injury - the person touches the object, generally the conductor, which the electric current flows by the strike.
- Side splash - branches form "jumping" from the primary flash channel, thrilling the person.
- Injuries - thrown and suffered dull trauma from shock waves (if very close) and possible hearing loss from thunder.
- Indirectly
- Ground flow or "step potential" - Earth's surface load races to the flash channel during discharge. Since the soil has a high impedance, the current "selects" a better conductor, often one's foot, passes through the body. The near instantaneous discharge rate causes the potential (difference) distance, which may reach several thousand volts per linear foot. This phenomenon is responsible for more injuries and deaths than the third composite above, with reports such as "hundreds of deer killed by lightning storms..." being a classic example.
- EMPs - the exhaust process produces an electromagnetic pulse (EMP) that can damage an artificial pacemaker, or affect a normal biological process.
- Secondary or results
- Explosion
- Fire
- Accident
Maps Lightning strike
Injuries
Lightning strikes can produce severe injuries, and have a mortality rate of between 10% and 30%, with up to 80% survivors experiencing long-term injuries. These severe injuries are usually not caused by thermal burns, because the currents are too short to heat the tissues; instead, nerves and muscles can be directly damaged by the high voltage that produces a hole in their cell membrane, a process called electroporation.
In direct attack, the electric current in the flash channel directly passes the victim. The relatively high reduction in voltage around the worse (like human) electrical conductor, causes the surrounding air to ionize and break down, and the external flashover diverts most of the main outflow so it passes around the body, reducing injury..
Metal objects that come into contact with the skin can "concentrate" the lightning energy, since it is a better natural conductor and preferred path, resulting in more serious injuries, such as burns from molten metal or evaporated. At least two cases have been reported in which the victim of a strike wearing the iPod suffered a more serious injury as a result.
However, during flash, the current flowing through the channel and around the body will produce large electromagnetic fields and EMP, which can cause electrical transients (spikes) in the nervous system or pacemaker, disrupting normal operation. This effect may explain cases where a heart attack or seizure follows a lightning strike that does not produce an external wound. It may also indicate that the victim is not directly attacked at all, but only because it is very close to the strike strike.
Another effect of lightning on the audience is their hearing. The shock waves generated from the thunder can damage the ears. Also, power failure to the phone or headphones can cause acoustic sound disturbance.
Epidemiology
One estimate is that 24,000 people are killed by worldwide lightning attacks every year and about 240,000 people are injured.
Another estimate is that the annual global death toll is 6,000.
According to NOAA, over the past 20 years, the United States averaged a fifty-year-old casualty, putting it second, just behind floods for deadly weather. In the US, between 9% and 10% of them die, with an average of 40 to 50 deaths per year (28 in 2008).
At Kisii in western Kenya, about 30 people die each year due to lightning strikes. The high level of Kisii's lightning death occurs due to the frequency of lightning storms and because many structures in the area have metal roofs.
This statistic does not reflect the difference between a direct strike, where the victim is part of the lightning line, an indirect effect as it is close to a termination point, such as a ground current, and a resultant, in which the victim emerges from the next event, such as a fire or explosion. Even the most knowledgeable first responders may not recognize a lightning-related injury, let alone a special one, a medical examiner, a police investigator or on rare occasions a trained lightning expert may have trouble identifying to accurately record. This ignores the fact that lightning, as the first event, can assume responsibility for the overall and consequential crash.
Direct attack victims can be much higher than the reported amount.
Effects on nature
Impact on vegetation
Trees are frequent conductors from lightning to the ground. Because the sap is a relatively poor conductor, the electrical resistance causes it to be explosively heated to vapor, which blows the bark outside the lightning line. In the following seasons, the trees grow too dense and may cover it completely, leaving only a vertical scar. If the damage is severe, the tree may not recover, and decay begins to rot, eventually killing the tree.
In sparsely populated areas such as Russia's Far East and Siberia, lightning strikes are one of the main causes of forest fires. Smoke and fog released by enormous forest fires can cause an electrical charge, initiating additional fires as far as several kilometers downwind.
Destroying rocks
When water in cracked rocks is rapidly heated by lightning strikes, the resulting steam explosion can cause rock and rock disintegration to shift. This may be an important factor in the erosion of tropical and subtropical mountains that have never been glaciated. The evidence of lightning strikes includes an erratic magnetic field.
Electrical and structural damage
Phones, modems, computers and other electronic devices can be damaged by lightning, because dangerous overcurrent currents can reach them through a telephone jack, Ethernet cable, or electrical outlet. Close strikes can also generate electromagnetic pulses (EMPs) - especially during a "positive" lightning release.
The lightning current has a very fast rise time, at the order of 40 kA per microsecond. Therefore, the conductor of the current indicates a marked skin effect, causing most of the current to flow through the outer surface of the conductor.
In addition to electrical wiring damage, other types of damage that might be considered include structural damage, fire, and property.
Prevention and mitigation
The field of lightning protection systems is a major industry worldwide because the impact of lightning can occur in human construction and activity. Lightning, due to the various traits measured across the whole order of such magnitude, can cause immediate or secondary effects; resulting in total destruction of facilities or processes or simply causing remote sensor electronic failure; it may result in outdoor activities being stopped for safety concerns to employees due to a storm near an area and until that has been enough; it can trigger volatile commodities that are stored in large quantities or disrupt the normal operation of an equipment in a critical time period.
Most lightning protection devices and systems protect the physical structure of the earth, the aircraft being an exception. While some attention has been paid to trying to control lightning in the atmosphere, all efforts have proven to be very limited in success. The concept of crystalline and silver iodide crystals is designed to deal directly with cloud cells and be distributed directly to the clouds of aircraft flying above it. Chaff is designed to handle electrical manifestations of storms from within, while silver iodide salting techniques are designed to deal with storm mechanical forces.
Lightning protection system
Hundreds of devices, including lightning rods and load transfer systems, are used to reduce lightning damage and affect lightning flash paths.
Lightning rods (or lightning rods) are metal strips or rods connected to the earth through conductors and earthing systems, which are used to provide the preferred path to the ground if the lightning ends in the structure. This product class is often called "finial" or "air terminal". The lightning rod or "Franklin's Rod" in honor of its famous inventor, Benjamin Franklin, is just a metal rod, and without connecting to a lightning protection system, as it sometimes happens in the past, will not provide additional protection for a structure. Other names include "lightning conductors", "arresters", and "discharges"; However, over the years these names have been incorporated into other products or industries with the protection of lightning protection. Lightning rods, for example, often refers to a fused link that explodes when a strike occurs to a high-voltage power line above the head to protect the more expensive transformers below the line by opening the circuit. In fact, it is the earliest form of heavy duty spike protection device (SPD). The modern arrester, built with metal oxide, is capable of sweeping high-voltage waves to the ground normally while preventing normal system voltage from shorted to ground.
System monitoring and warning
The exact location of the lightning strike or when it will happen is still impossible to predict. However, products and systems have been designed with varying complexities to warn people as the possibility of strikes rises above levels determined by risk assessment for site conditions and circumstances. One significant improvement is in the field of flash detection through both satellite and ground based observation devices. Strikes and atmospheric flashes are unpredictable, but the level of detail recorded by this technology has greatly improved in the last 20 years.
Although commonly associated with lightning storms at close range, lightning strikes can occur on a seemingly cloudless day. This event is known as "A Bolt From the Blue"; lightning can strike up to 10 miles from the clouds.
Lightning interrupts AM radio signals (amplitude modulation) far more than FM signals (frequency modulation), providing an easy way to measure the intensity of local lightning attacks. To do so, one must set a standard AM receptor to a frequency without a transmitting station, and listen to cracking between static. Stronger or nearer lightning bolts will also cause cracks if the receiver is set to the station. Because lower frequencies spread further along the ground than in high frequencies, undersea wave frequency (MW) (in the 500-600 kHz range) can detect lightning strikes at longer distances; if longwave band (153-279Ã, kHz) is available, using it can increase this range even further.
Lightning detection systems have been developed and can be used in locations where lightning strikes present special risks, such as public parks. Such systems are designed to detect conditions that are believed to support lightning strikes and warn people around them to enable them to take the appropriate cover.
Personal security
The US National Lightning Safety Institute advises Americans to have a plan for their safety during a storm and immediately start when the first lightning is seen or lightning is heard. This is important because lightning can strike without rain actually falls. If thunder can be heard at all, then there is a risk of lightning. The safest place is inside the building or vehicle. The risk remains up to 30 minutes after the last lightning or thunder is observed.
The National Lightning Safety Institute recommends the use of the F-B method (flash to boom) to measure the distance to a lightning strike. Lightning strikes of lightning and thunder occur at almost the same time. But light travels 300,000 kilometers in seconds, almost a million times the speed of sound. The sound moves at a lower speed of 344 m/s, so lightning flashes visible before the thunder is heard. The method for determining the distance between lightning strikes and the viewer, involves the counting of seconds between lightning and thunder. Then divide by three to determine the distance within kilometers, or five miles. An immediate lightning precaution should be taken if the F-B time is 25 seconds or less, ie if the lightning is closer than 8 km (5.0 million).
Different reports on what to do if caught outside during a storm. One study showed that prostration is safer than lying flat when there is no other alternative. A contrasting report suggests that it does not matter whether someone stands, squats, or lies while out in a lightning storm, because lightning can run on the ground; this report suggests to be within the most secure structure or vehicle. In the United States, the annual average death rate due to lightning is 51 deaths per year, although there are only 23 deaths in 2013, which is a record low; Most risky activities include fishing, boating, camping, and golf. A person who is 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 brain stem, which controls breathing.
Several studies conducted in South Asia and Africa show that the dangers of lightning are not considered serious enough there. A team of researchers from the University of Colombo found that even in environments that have experienced deaths from lightning, no precautions are taken against future storms. An expert forum was held in 2007 to discuss how to increase awareness of lightning and improve lightning protection standards, and expressed concern that many countries do not have official standards for the installation of lightning rods.
The famous incident
All events related or suspected to cause damage are called "lightning incidents" because of four important factors.
- The forensic evidence of lightning retreat, in the best investigated example, is very small (a hole in the metal smaller than the point of the pen) or inconclusive (dark color).
- Objects that are struck may explode or subsequent fires destroy any small evidence that may be available immediately after the strike itself.
- The flash and debit channels themselves are not the only cause of injury, ignition or damage, ie, ground currents or explosions of combustible materials.
- Human sensual acuity is not as good as the duration of millisecond lightning flashes, and our ability to observe this event is subject to the inability of the brain to perceive it. Lightning detection systems are online, both satellite and ground based, but accuracy is still measured in the hundreds to thousands of feet, rarely allowing them to pinpoint the exact stop location.
Source of the article : Wikipedia
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