Lightning Statistics, History & Protection
Lightning is an atmospheric discharge of electricity, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. The leader of a bolt of lightning can travel at speeds of 60,000 m/s and can reach temperatures approaching 30,000 °C (54,000 °F), hot enough to fuse soil or sand into glass channels.
There are over 16 million lightning storms every year. Lightning is a major cause of building fires, even though highly effective protection against this threat has long been available. The Empire State Building is struck by lightning on average 23 times each year, and was once struck 8 times in 24 minutes. Roy Sullivan held a Guinness World Record after surviving 7 different lightning strikes across 35 years.
In the 1700s Benjamin Franklin proposed a method of protecting structures from the effects of lightning. His method was based on observations that suggested lightning preferentially strikes elevated objects and lightning currents can be carried to and dissipated in earth by a suitable network of conductors and grounding electrodes.
Various approaches aimed at providing protection against lightning, similar to Franklin's method of elevated rods and down-conductors, have been tried over the past 250 years; the more successful designs have been described and published as standards for guidance and protection of the public.
In 1904, The National Fire Protection Association of Quincy, MA, established the American standard for installation of lightning protection systems. Now known as NFPA 780, The Standard for the Installation of Lightning Protection Systems is revised periodically by an NFPA technical committee to incorporate new knowledge about the physics of lightning and advances in technology.
It is well established that properly installed and maintained conventional structural lightning protection systems (LPS) based on Franklin's methods significantly decrease lightning damage. Several different types of devices, including lightning rods and electrical charge dissipaters, are used to prevent lightning damage and safely redirect lightning strikes.
The installation of such a system in conformance with NFPA 780 is not a simple matter.
A lightning rod (or lightning protector) is a metal strip or rod, usually of copper or similar 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 systems in general or specific components within them.
Lightning protection systems alter lightning streamer behavior. Proper procedures must be followed for the protection to be effective.
To provide effective protection for structures, a lightning protection system must include:
A sufficient number of rods must extend above the upper portions of the structure to be protected and their tips must be so exposed that one of them becomes the locally-preferred strike receptor upon the close approach of a leader, descending from a thundercloud.
The connections between the strike receptor and the earth, namely the "main conductors" and the "down conductor system," must be able to carry the rapidly-varying lightning current without significant heating and without dislodging.
The impedance to the flow of current in the down conductor must be sufficiently low that "side flashes" to objects in the vicinity do not occur as a result of high voltages developed by the passage of the current.
The connections from the down conductors to the earth must allow the lightning current to flow into the ground without the development of large electrical potential differences on the earth's surface and without creating hazards to personnel or structures nearby.
All nearby metal components of the structure must be electrically bonded to its down-conductor system the probability of "side flashes." Given this complexity in designing effective lightning protection systems, standards that specify the requirements which must be met to ensure the adequacy of each lightning protection installation are essential and are required by most industrialized nations.
The American standard represents nearly 250 years of practical experience and about 100 years of consensus among specialist in the physics of lightning, of manufacturers of lightning protection equipment, and of lightning protection installers.
The members of the AMS Committee on Atmospheric Electricity have reviewed the modern practices of lightning protection and have concluded that NFPA 780 is a useful standard with sound scientific basis. The Society recognizes the need for lightning protection standard and supports the current American edition specifying the installation of lightning protection systems. Additional background material can be found in Background for the AMS statement on Lightning Protection Systems by C.B. Moore.
The month of June is typically known among meteorologists for promoting lightning safety awareness, because June is the first month of summer and brings thunderstorms.
Regarding Safety Awareness... did you know that lightning can strike indoor pools, directed into the pump by electrical circuits from outdoor power poles?
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For more information on how Ocean Electric Corp. can provide solutions to your Lightning Protection Issues, call.
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Ocean Electric Corp.
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Southampton, NY 11968
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