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"Human Voltage... What happens when people and lightning converge"
(Source: NASA Space Science News, 6/18/99) <snipped>
[This story from the quadrennial International Conference on Atmospheric
Electricity, June 7-11, 1999, in Guntersville, Ala.]
-------------------
Either lightning is attracted to testosterone, or men spend an
inordinate
amount of time outdoors swinging metal objects about. Men are struck by
lightning four times more often than women.
According to a study entitled "Demographics of U.S. Lightning Casualties
and Damages from 1959 - 1994," by Ronald L. Holle and Raúl E. López of
the
National Severe Storms Laboratory and E. Brian Curran of the National
Weather Service, males account for 84% of lightning fatalities and 82%
of
injuries.
Men can take comfort in the fact that the actual number of deaths and
injuries from lightning strikes has decreased in the past 35 years.
Holle's team attributes 30 percent of the decrease in lightning deaths
to
improved forecasts and warnings, better lightning awareness, more
substantial buildings, and socioeconomic changes. They attribute an
additional 40 percent to improved medical care and communications.
The National Weather Service publication Storm Data recorded 3,239
deaths
and 9,818 injuries from lightning strikes between 1959 and 1994. Only
flash floods and river floods cause more weather-related deaths. But
according to Dr. Elisabeth Gourbière of the Electricitie de France,
Service des Etudes Médicales, only 20 percent of lightning victims are
immediately struck dead. Still, many doctors do not fully understand how
to treat the injuries of the other 80 percent of lightning victims who
survive a strike.
Says Gourbière, "The pathology of lightning, or keraunopathy, is known
only to a few specialists."
Lightning injuries are not the same as electrical shocks. For one thing,
the contact voltage of a typical industrial electrical shock is 20 to 63
kilovolts, while a lightning strike delivers about 300 kilovolts.
Industrial shocks rarely last longer than half a second (500
milliseconds)
because a circuit breaker opens or the person is thrown far from the
live
conductor. Lightning strikes have an even shorter duration, only lasting
up to a few milliseconds. Most of the current from a lightning strike
passes over the surface of the body in a process called "external
flashover."
If you survive a shock, you still have to deal with the consequences of
the electrical burns. Industrial shock burns can lead to kidney failure,
infection, muscle and tissue damage, or amputation. Lightning burns are
exceptionally life threatening. Gourbière says that 70 percent of
lightning survivors experience residual effects, most commonly affecting
the brain (neuropsychiatric, vision and hearing). These effects can
develop slowly, only becoming apparent much later.
Many lightning victims had been walking in an open field or swimming
before they were struck. Other lightning victims had been holding metal
objects such as golf clubs, fishing rods, hay forks, or umbrellas. But
even those not holding metal objects are as likely to be struck by
lightning as a bronze statue of the same size.
When you hear thunder, you are already within the range where the next
ground flash may occur. N. Kitagawa of Central Lightning Protection,
Inc.
and A. Sugita and S. Takahashi of Franklin Japan determined the average
intervals between lightning strikes in order to estimate how much time
someone has to seek shelter. Their news is far from encouraging.
"It is concluded that there exists no safe time interval during which a
human is free from direct strikes," they wrote.
In an area with a radius of 500 meters (1,640 ft), most of the intervals
between lightning strikes range from 0 to 600 seconds, with a maximum
frequency of 40 seconds. To avoid being struck by lightning, you should
seek shelter when you hear even the faintest thunder. Some of the best
places to take refuge are enclosed buildings, or cars and buses (but
don't
touch the metal!). In case there are no safe spaces nearby, bend into a
crouching position until there is a break in the storm.
Isolated trees, telephone booths, and open structures like gazebos or
porches make poor lightning shelters. If there is a tall object nearby,
move as far away as possible - at least 2 meters (7 ft). Standing next
to
tall isolated objects like poles or towers makes you vulnerable to
secondary discharges coming off those objects. The mechanism for how
towers attract lightning is not really understood. But scientists have
known for a long time that towers attract more lightning than the
undisturbed ground nearby.
Lightning damages have been on the increase in the past 35 years.
Holle's
team attributes most of this increase to population growth. Storm Data
recorded 19,814 property-damage reports due to lightning in the United
States from 1959-1994. Pennsylvania has the largest number of damage
reports, while the highest rates of damage reports weighted by
population
are on the plains from North Dakota and Oklahoma.
The National Weather Service Storm Data figures place the most recent
yearly losses at $35 million, but the process by which this figure is
tabulated is open to error. Storm Data collects much of its severe
weather
information from newspaper reports. If an incident is not reported in
the
paper or is overlooked by the Storm Data reviewer, it may not get into
the
publication's statistical base.
There are currently several different methods used to keep track of
lightning strikes, but none of them can be considered perfect. Medical
reports, for instance, sometimes report "burns" as the primary cause of
death, with lightning listed as a secondary effect. Despite such
instances
of underreporting, the methods used in the United States to track
lightning strikes are considered to be the best available.
In the contest between people and lightning, lightning wins. Although
lightning rarely strikes more than one person at a time, over the course
of a year the damages, deaths and injuries add up to make lightning a
serious threat. By studying the outcome of human-lightning encounters,
scientists hope to find more ways to prevent such meetings from
occurring
in the first place.
Footnote--
Feel the Burn: If you'd like to experience a lightning strike, go
golfing
one Sunday in July around 4 p.m. If you're really determined, be sure
you
do it in Florida. Florida has twice as many lightning casualties (deaths
and injuries combined) as any other state. Most lightning casualties
occur
in the afternoon - two-thirds between noon and 4 p.m. local standard
time
with a casualties maximum at 4. Sunday has 24% more deaths than other
days, followed by Wednesday. Lightning reports reach their peak in July.
//end//
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