NLSI presents the following random factoids for readers who need to
tell others about lightning. From students to network newsies...this stuff
is for you. It’s like fertilizer...it’s intended to be spread
around.
NLSI is a
group concerned with lightning safety issues. We conduct several types
of education seminars. We perform site audits and we inspect facilities
to assure "best available technology" for lightning safety.
We have no products to sell. We represent no special interest group.
What is lightning?
It is static electricity gone giant-scale. Lightning comes from thunderstorms
(and snowstorms and volcanoes). There are some 2000 thunderstorms globally
at any one time producing some 100 lightning strikes to earth per second.
In the USA, there are about 15-20 million ground strikes per year. Florida
has the most strikes - about 12 strikes per square kilometer per year
in some places. On average, more people are killed by lightning than
any other weather event. There is more than $2 billion damage annually
in the USA from lightning. (More information about losses
from lightning is available.
Your risk of being killed by lightning is 1:28,500
per exposed individual. (NPH Newsletter January, 1992)
The average flash will light a 100 watt bulb
for more than 3 months.
Lightning’s heat exceeds 50,000 degrees
F. or three times hotter than the surface of the sun. Its’ speed
is 90,000 miles per second (one hundred million feet per second). The
average thickness of a bolt is 1-2 inches.
It’s wrong to say lightning can be "stopped"
or prevented. It is a totally capricious, stochastic (look that up !)
and unpredictable event.
The "lightning code" in the USA is
called NFPA-780-1995 and was written by lightning rod salesmen. Compare
it with the European code, TC-81, written by scientists and engineers.
Thunder is always associated with lightning.
Thunder is the shock wave created by super heated air in the lightning
channel.
Some good specialized publications on lightning
are:
- General subject matter:- Uman, M "Lightning", Dover, 1984.
- Uman, M "All About Lightning", Dover, 1986.
Viemeister, P,"The Lightning Book", MIT, 1972.
- Medical subjects: - Seminars in Neurology, Parts I & II (Sept
& Dec 1995)
- Thunderstorms: - Kessler, E "Thunderstorms, A Social, Scientific,
and Technological Documentary", U. OK Press, 1992.
- General Weather: Williams, J "The Weather Book", Vintage
Bks, 1992.
- Weird Weather Phenomena: Corliss, W "Lightning, Auroras, Nocturnal
Lights and related luminous phenomena", Sourcebook, 1992.
Nine out
of ten people struck by lightning survive the event. But nearly 25%
of these survivors suffer long term psychological or physiological trauma.
The best defense against lightning is preparedness. (For more information,
see Personal Lightning Safety Tips.
Please pass this around.)
What’s good about lightning? It produces
a lot of the nitrogen compounds that are important for plant growth.
It provided early man with his only source of fire. It’s better
than fireworks on the Fourth of July and it’s free !
The average lightning strike contains 20,000
amps. An arc welder uses 250- 400 amps to weld steel. Your house probably
uses only 200 amps. Current in excess of 20 milli amps can cause your
chest muscles to contract, stopping breathing.
The worst lightning incident (so far) in the
USA was in New Jersey, on July 10, 1926. A Navy ammunition arsenal was
hit, killing 19 people and destroying property valued at $17 million
(1986 dollars). Usually, single events caused by lightning are less
dramatic than single events caused hurricanes, floods or tornadoes.
If you are the victim, however, it is plenty dramatic.
It’s
wrong to say lightning never strikes twice. It hits the Empire State
Building, on average, 21-25 times per year. A US Park Service Ranger,
Ray Sullivan, was struck by lightning seven different times between
1942 and 1976. Yep, he survived them all. (We don't know if his hair
was curly.)
Beware of sheltering under tall trees during
a storm. (Trees contain some 20% moisture content. We humans have 65%
moisture content.) Lightning coming down a tree wants to follow the
path of least resistance: TAG - YOU’RE IT ! Get to an all metal
vehicle like a car or a truck if you can. That’s the safest place.
