Lightning safety
2449741
224348379
2008-07-08T13:30:52Z
Tdreyer1
1855701
/* Lightning rods */ adding a link to "lighting protection syestem"
{{For|lightning-related injuries|Keraunomedicine}}
[[Image:Lightning in Arlington.jpg|thumb|right|222px|Lightning is a highly visible form of [[energy]] transfer.]]
[[Thunderstorm]]s are the primary source of [[lightning]]. Because people have been struck many miles away from a storm, seeking immediate and effective shelter when thunderstorms approach is an important part of '''lightning safety'''.
Contrary to popular notion, there is no 'safe' location outdoors. People have been struck in sheds and makeshift shelters. A better alternative is to seek shelter within an enclosure of conductive material (such as an automobile which is an example of a crude type of [[Faraday Cage]]).
Once inside the enclosure, it is advisable to keep away from any attached metallic components (such as keys in an ignition, etc...). If thunder can be heard, there is a risk of being struck.
==Incidence of strikes==
[[Image:Global lightning strikes.png|thumb|300px|right|World map showing frequency of lightning strikes, in flashes per km² per year (equal-area projection). Combined 1995–2003 data from the Optical Transient Detector and 1998–2003 data from the Lightning Imaging Sensor.]]
Nearly 2000 people per year in the world are injured by lightning strikes. In the USA between 9-10% of those struck die,<ref> Cherington, J. et al. 1999: Closing the Gap on the Actual Numbers of Lightning Casualties and Deaths. Preprints, 11th Conf. on Applied Climatology, 379-80.[http://www.uic.edu/labs/lightninginjury/Disability.pdf].</ref> amounting to an average of 75 fatalities annually.<ref>''Mythbusters ("Son of a Gun")''. '''The Discovery Channel'''.</ref> In the United States, it is the #2 weather killer (second only to [[flood]]s), killing 100 annually and injuring ten times that number.<ref name="lightningsafe">http://www.lightningsafety.noaa.gov/resources/Ltg%20Safety-Facts.pdf OSAA Lightning Safety Facts</ref> The odds of an average person living in the USA being struck by lightning in a given year is 1:700,000.
[[Roy Sullivan]] has the record for being the human who has been struck by lightning the most times. Working as a park ranger, Roy was struck seven times over the course of his 35 year career. He lost a nail on his big toe, and suffered multiple injuries to the rest of his body.<ref>http://www.guinnessworldrecords.com/content_pages/record.asp?recordid=48497 Roy's record at Guinness.</ref>
==Path to victim==
Lightning can incapacitate humans in four different ways:
* Direct strike
* 'Splash' from nearby objects struck
* Ground strike near victim causing a difference of potential in the ground itself (due to resistance to current in the Earth), amounting to several thousand volts per foot, depending upon the composition of the earth that makes up the ground at that location (sand being a fair insulator and wet, salty and spongy earth being more conductive).
* [[Electromagnetic pulse|EMP]] or electromagnetic pulse from close strikes - especially during positive lightning discharges
In a ''direct hit'' the [[electrical charge]] strikes the victim first. Counterintuitively, if the victim's skin [[electrical resistance|resistance]] is high enough, much of the current will ''flash'' around the skin or clothing to the ground, resulting in a surprisingly benign outcome. Metallic objects in contact with the skin may concentrate the lightning strike, preventing the flashover effect and resulting in more serious injuries. At least two cases have been reported where a lightning strike victim wearing an [[iPod]] suffered more serious injuries as a result.<ref> {{cite journal |author=Vastag B |title=fryPod: Lightning strikes iPod users |journal=Science News |volume=172 |issue=3 |year=2007}}</ref>
''Splash'' hits occur when lightning prefers a victim (with lower resistance) over a nearby object that has more resistance, and strikes the victim on its way to ground.
''Ground'' strikes, in which the bolt lands near the victim and is conducted through the victim and his or her connection to the ground (such as through the feet, due to the voltage ''gradient'' in the earth, as discussed above), can cause great damage.
==Safety mechanisms==
[[Image:Pointed Lightning Rod.jpg|left|thumb|150px|An example of a standard, pointed-tip, air terminal.]]
===Prevention===
Several different types of devices, including [[lightning rod]]s and electrical charge dissipators, are used to prevent lightning damage and safely redirect lightning strikes.
=====Lightning rods=====
[[Image:Lightning warning system 1.jpg|right|thumb|222px|A Thor Guard [[lightning prediction system]]]]
{{main|Lightning rod}}
A lightning rod (or lightning protector) is a [[metal]] strip or rod, usually of [[copper]] or similar [[conductor (material)|conductive]] material, used as part of lightning safety to protect tall or isolated structures (such as the roof of a building or the mast of a vessel) from [[lightning]] damage. Its formal name is ''lightning finial'' or ''air terminal''. Sometimes, the system is informally referred to as a lightning conductor, arrester, or discharger; however, these terms actually refer to [[lightning protection system]]s in general or specific components within them. Lightning protection systems alter lightning streamer behavior. The field of lightning protection is almost totally void of systems or concepts designed to deal with the general problem area as a whole. Chaff and silver iodide crystals 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.
===Predicting strikes===
Although commonly associated with close thunderstorms, lightning strikes can occur on a day that seems devoid of clouds. This occurrence is known as "A Bolt From the Blue"<ref>[http://www.crh.noaa.gov/pub/ltg/crh_boltblue.php NWS Pueblo Lightning Page - Bolts From The Blue<!-- Bot generated title -->]</ref> and is because 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.<ref>[http://www.patentstorm.us/patents/7254484-description.html Detection of lightning - US Patent 7254484<!-- Bot generated title -->]</ref> 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 [[Noise (radio)|static]]. Stronger or nearby lightning strikes will also cause cracking if the receiver is tuned to a station.
[[Lightning prediction system]]s 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.
=====Estimating distance=====
The National Lightning Safety Institute recommends using the F-B (flash to boom) method. The flash of a lightning strike and resulting thunder occur at roughly the same time. But light travels at 300,000 kilometers in a second, almost a million times the speed of sound. Sound travels at the slower speed of 344 m/s so the flash of lightning is seen before thunder is heard. To use the method, count the seconds between the lightning flash and thunder. Divide by 3 to determine the distance in kilometers, or by 5 for miles. All of the precautions above should be taken from the time the F-B is 25 seconds or less, that is, the lightning is closer than 8 km (5 miles). Do not rely on the F-B method for determining when to relax the safety measures, because lightning typically occurs in multiple locations, and just because some strikes are far away does not mean another is not close. Precautions should not be relaxed until thunder cannot be heard for 30 minutes.
<!--==Trivia==
* In the Spider-Man comics, the villain Electro got his powers from being struck by lightning whilst working on a power line.
* Golfers [[Retief Goosen]] and [[Lee Trevino]] have both been struck by lightning while playing.<ref>http://www.golfeurope.com/almanac/players/trevino.htm</ref>
* Colombian soccer player [[Herman Gaviria]] a.k.a Carepa, was struck by lightning during a training session in [[Cali]], [[Colombia]] and died at the age of 37. Ironically, before starting the session, he said "Lightning is not going to kill me." -->
=====Removing sensitive equipment=====
When there is a risk of thunderstorms, it is recommended that [[Telephone|telephones]], [[Modem|modems]]<ref>
{{cite journal
| title = Summer tips for telecom users
| journal = blog.anta.net
| date = [[2008-06-17]]
| url = http://blog.anta.net/2008/06/17/summer-tips-for-telecom-users/
| issn = 1797-1993
| accessdate = 2008-06-18 }}
</ref> and other devices that could be damaged by lightning should be unplugged, thereby preventing harmful [[Overcurrent|overcurrent]] from reaching them through the [[Jack (connector)|phone jack]] or [[AC power plugs and sockets|electricity outlet]].
== References ==
{{refs|2}}
== External links ==
* [http://www.edu4hazards.org/lightning.html How to survive lightning] A guide for children and youth
* [http://www.lightning-strike.org Lightning Strike & Electric Shock Survivors International, Inc.], a non-profit support group by and for survivors, their families, and other interested parties.
* [http://www.cting.hr/eng/development.aspx Lightning risk assessment application according European IEC 62305-2 norm.]
[[Category:Lightning]]
[[Category:Electrical safety]]
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[[uk:Грозозахист]]