Subj: Newsletter - MHE - Lightning Protection
Date: 3/9/2000 8:11:05 PM Eastern Standard Time
From: mike@mikeholt.com

This newsletter was sent from Mike Holt Enterprises (www.mikeholt.com) 

*--------------------------------------------------------------------------------------------*
Lightning: 'If You Can See It, Flee It'

Johannesburg (Business Day, March 7, 2000) - The lightning strike that killed businessman Glyn Riley at Johannesburg Country Club on Saturday suggests just how freakish the phenomenon can be - and how such accidents might be avoided in future.

Two friends of the late CEO of Northern Engineering Industries, Brian Stott and Ian Cruickshank, who took cover with Riley under a wooden shelter, are in hospital.

The bolt did not strike the shelter, but the ground a short distance away, and streaked across the wet turf bound for the shelter's foundations. According to the US National Lightning Safety Institute, there is no such thing as a lightning-proof small outdoor shelter. However, it says, a certain type of protection system could make the difference between life and death. The key lies in the concept of the Faraday cage, which at its most rudimentary is made up of a grid of conductor pipes on each edge of a cube - and crucially, buried on the bottom sides encircling the structure. In theory, provided you do not touch the conducting metal sides, you should be relatively safe - even if a bolt shoots towards you at ground level. Such earthing would also intercept underground electrical arcs that may shoot off a nearby object (such as a tree) struck by lightning.

This past weekend's fatality raises questions about the statistical likelihood of a person being killed by lightning. Geography plays a big factor. The mean number of lightning deaths per million is 0,2 in the UK but climbs to 0,6 per million in the US, 1,5 in SA and a whopping 1,7 per million killed annually in Singapore. Central Florida in the US experiences about 10 to 15 lightning strikes per square kilometer every year. Parts of Africa, Southeast Asia and mountainous regions of Latin America experience strikes at a rate double or triple that figure. Golfers have a much higher likelihood of being struck, mainly because they are most likely to be caught in the open far from shelter. In addition, according to the US National Aeronautics and Space Administration, men are struck by lightning four times more often than women - but only 20% of victims are immediately struck dead.

The truly terrifying fact about lightning is how little the average person respects it. Did you know, for instance, that when you hear thunder – no matter how far away it appears to be - you are already within the range where the next ground flash may occur? According to the lightning institute, lightning "leaders" from thunderclouds electrify objects on the ground as they approach the earth, from many kilometers away. "Ground-based objects may launch lightning streamers to meet these leaders. Streamers may be heard (some say they sound like bacon frying) and seen (we may notice our hair standing on end). "A connecting leader-streamer results in a closed-circuit cloud-to-ground lightning flash. Thunder accompanying it is the acoustic shock wave from the ... discharge."

In this situation, a good place to find is a car or bus with the windows completely shut. This forms a version of the Faraday cage. (By the way, rubber tires provide no safety from lightning. After all, lightning has traveled for a great distance through the sky: 10cm or 12cm of rubber will provide no insulation whatsoever). The exterior of the vehicle carries most of the electricity. In a strike, the institute says, a person should not touch any metallic objects linked to the outside of the car. These include door and window handles, radio dials, CB microphones, gearshifts, and steering wheels. Put your hands in your lap and hope for the best. 

If there is no car nearby, find a clump of shrubs of uniform height, or a ditch, trench or any low ground. Get at least 5m away from other people. Bend into a crouching position with your feet together and your head down. Do not even think of sheltering under an isolated tree or an open structure like a gazebo. If there is a tall object nearby, move as far away from it as possible. Standing next to poles or towers makes you vulnerable to secondary discharges from those objects.

Richard Kithil, president and CEO of the institute, suggests that if you are lucky enough to have found shelter during an electrical storm, remain there for 30 minutes after you last observe thunder or lightning. His maxim is: "If you can hear it, clear it. If you can see it, flee it." 

On a lighter note, the US-based Statistical Assessment Service supports the notion that a person is more likely to be struck by lightning than to win the lottery.


Africa News Service, Jeremy Thomas, March 07, 2000
Copyright 2000 Business Day. Distributed Via Africa News Online.

This notice was supplied to me from:
Fredrick Rea O'Keefe, fredrick@tech-center.com
Moderator, LightningProtection@ONElist.com

Mike Holt
Mike Holt Enterprises

*---------------------------------------------------------------------------------------------*