[Rhodes22-list] More on Lightning

Sat Dec 13 13:09:18 EST 2003

what is still not clear is which is better, no path to ground or a great path to gound.

MJM

----- Original Message ----- 
From: "Robert Quinn" <rjquinn at bellsouth.net>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Saturday, December 13, 2003 11:53 AM
Subject: [Rhodes22-list] More on Lightning

> Just in case you would like some more tid bits on lightning. 
> 
> 
> Subject: [Fwd: TWL: From the experts on lightning (long)]
> Interesting.
> 
> -------- Original Message --------
> Subject: TWL: From the experts on lightning (long)
> Date: Tue, 2 Dec 2003 04:24:46 -0600
> From: "Keith" <klemmons at airmail.net>
> To: <trawler-world-list at lists.samurai.com>
> 
>  >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
> marinemed at earthlink.net
> 
> 
> 
> 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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> 
> --
> Nick Meloy
> 44' Custom Trawler  "Serendipity"
> mulatfl at att.net  30 32.855 N  87 07.550 W
> (850) 994-6165
> 
> 
> > 
> 
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