dave@egh.com wrote:
> My tallest tower is now only 85 feet tall, yet I have had towers
> above tree level for almost 15 years and have yet to experience a lightning
> hit. The towers are grounded, yet I am not sure how good the ground is at
> this point in time. To what do I attribute my lightning-free experience?
> Only Divine providence. However, the moral of the story is that you should
> not expect to be safe from lightning strikes simply because there are taller
> objects nearby than your tower.
well, maybe divine prvidence and a bit of statistics.
consider a 30m high tower. use a 45 degree angle down from the top of
the
tower (a 45 degree angle is a commonly used estimate for how big of an
area
is 'protected' by a tall pole or wire). This means that any stroke in
an
area of about 2800 square meters around the tower may strike the tower
instead of the ground. i don't remember the statistics for your area,
but
out here in western mass there are about 4 strokes per square kilometer
per
year on the average. this means 4 strokes in 1,000,000 square meters
per
year.... so your 2800 square meter area would get 4*2800/1000000 or
about
.0112 strokes per year, or about one stroke every 89 years that may hit
the
tower itself, or may ignore it and still hit the ground.
--
David Robbins K1TTT (ex KY1H)
k1ttt@berkshire.net or robbins@berkshire.net
http://www.berkshire.net/~robbins/k1ttt.html
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|