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From: Keith (no email)
Date: Tue Dec 02 2003 - 05:24:46 EST
>From Ocean Navigator's e-mail newsletter:
_______________________________-
Title: From the Experts on Lightning
By: Jeffrey Isaac, PA-C
When there are very few real experts on a subject, it is a rare and
wonderful privilege to learn directly from one of them. Such an
opportunity was presented when Dr. Mary Anne Cooper was invited to speak
at the annual meeting of Wilderness Medical Associates instructors in
October. Cooper is an experienced emergency physician and researcher at
the University of Illinois at Chicago, and one of the world's two or three
leading experts on lightning and lightning injuries.
One of the benefits, and risks, of speaking directly to the source is that
they sometimes share information that is not yet ready to print. One of
the risks of dealing with something like lightning is that, just when you
print it, something completely different happens. So, as I share what I've
learned, please keep these caveats in mind.
Over an 80-year life span, your chances of being involved in a lightning
strike are about 1 in 3,000 (averaged worldwide stat). There is no
statistical significance to someone being struck more than once. It's just
the luck of the draw and geographic circumstance. Specific people do not
attract lightning more than others.
Metal does not attract lightning, either. The only two factors that
influence the probability of a strike are the height and isolation of an
object. In fact, the probability of a strike increases by the square of
the object's height. Add a 1-meter antenna to your 20-meter mast, and you
increase your probability of being struck by 10.75 percent.
Devices claiming to reduce your chances of being struck, by bleeding ions
or electrostatic charge off of your masthead, do not work. If the device
increases your mast height, it will actually increase your probability of
being struck. This opinion was rendered in response to my direct question
on the subject, and was unequivocal.
Lightning progresses toward the ground or water in a series of stepped
leaders, penetrating 30 to 50 meters through the atmosphere a split-second
at a time until contact is made. The resulting column of ionized air
becomes the conduit through which the electric potential between ground
and cloud is equalized. This gives lightning a visual field of only 50
meters max. In other words, the stepped leader would have to come within
30 to 50 meters of your masthead to "see" it.
This explains why the Cone of Protection concept we'd been teaching is
inaccurate. The idea was to locate yourself within the 45 degree cone
below the top of a tall object, assuming that the object would be struck
instead of you. Cooper dispelled this myth with a photograph of the space
shuttle being struck on the launch pad in Florida. The lightning bolt
curved around the huge lightning rod on top and into the base near the
tail of the spacecraft. NASA has since re-arranged their lightning
protection into a web of cables strung from the top of the gantry slanting
outward to the ground. It sounds kind of like standing rigging, doesn't
it?
While metal does not attract a lightning strike, it does do a fine job of
conducting it once struck. The best grounding system is a straight shot of
metal conductor to a large (1-square-meter minimum) ground below the
waterline. An aluminum mast stepped directly on a lead keel would be
nice.
There is no truth to the idea that a grounding system increases your
boat's chance of being hit. If you do get struck, a robust ground system
can prevent damage and injury. Just be sure to watch the storm from the
cockpit, not while leaning on the backstay.
As you construct or evaluate your grounding system, remember that
lightning does not like to follow sharp bends or corners. It will jump
across or through a less conductive medium instead. The increased
resistance will release heat, vaporizing any moisture in the material.
This is how fiberglass or wooden hulls explode when struck.
As a side note, I will be interested in the results of lightning strikes
on boats with fiber rope for standing rigging. Aramid fiber melts at a
relatively low temperature. It is also brittle, I wonder what a blast of
superheated steam would do to it.
Your best protection from lightning is storm avoidance. If you do get
caught, spend as little time exposed to the thunderstorm as possible.
Lying hove-to while it passes over may be a better choice than running
with it.
Of the people involved in a lightning strike, 90 percent survive. Of
those, 70 percent may experience some type of permanent disability. The
only direct cause of death from lightning is cardiac arrest. Burns are
rarely serious. People do not turn into crispy critters. Secondary injury
and death can occur as a result of falls or drowning following a strike.
Lightning injuries include everything you might expect from a nearby
explosion. Superficial burns are caused by vaporized sweat. They tend to
be more serious where the steam is held against the body, such as inside
foul-weather gear.
There is no special emergency treatment for a lightning strike; just treat
what you see. If the victim was involved enough to sustain visible injury
or was knocked down by the jolt, seek follow-up medical evaluation when
possible.
Lightning victims do not remain charged. It is safe to handle them
immediately. Even if the victim appears dead, attempt cardio-pulmonary
resuscitation. Lightning acts like a defibrillator, stopping the
electrical activity of the heart. It also will stop respiratory effort.
Since the heart is somewhat automatic, it may restart on its own while you
continue to supply air to the victim. Don't give up until you've tried CPR
for 30 minutes without restoring a pulse.
For more information, see Dr. Cooper's website at:
http://cms.navigatorpublishing.com/enewsl.asp?l=228
-- Jeffrey Isaac
Related Articles
Title: Lightning hit causes extensive damage
http://cms.navigatorpublishing.com/enewsl.asp?l=229
Title: Lightning protection a qualified success
http://cms.navigatorpublishing.com/enewsl.asp?l=230
Title: 1800s lightning protection pioneer
http://cms.navigatorpublishing.com/enewsl.asp?l=231
Author Bio:
Jeff Isaac is a licensed physician assistant with a particular interest in
back-country and marine medicine. He holds a 100-ton master's license and
is an experienced bluewater sailor, having logged thousands of miles
aboard his 31-foot sloop October, as well as sail training and
oceanographic research vessels. Jeff teaches medicine with the Ocean
Navigator School of Seamanship and has been an instructor of wilderness
medicine and rescue with Wilderness Medical Associates for over 20 years.
He currently lives in Crested Butte, Colo., where he practices with the
Crested Butte Search and Rescue. Jeff is a frequent contributor to Ocean
Navigator and is author of the Outward Bound Wilderness First Aid
Handbook, published by Lyons and Buford.
Keith
__
Is there another word for synonym?
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