[Gllug] Lightning - was Evolution won't fetch my mail (Help)

[Chris Bell]

On Sat 10 Aug, Mark Preston wrote:

> 
>    Surprisingly, the way that people die in a lightning strike is not a 
> result of severe burns, as most people think, but because the electrical 
> force shocks the heart into cardiac arrest and cuts off breathing by 
> paralyzing the chest muscles.
> 


   There was a BBC programme in the Science Shack series which dealt with
high voltages, sparks, and lightning. They used the National Grid test lab
to demonstrate the screening effects of Faraday cages, lightning conductors,
and the whole body woven stainless steel mesh protective clothing worn by
engineers working on the live grid. The grid is AC, so they could draw about
a 12 inch spark by holding a gloved hand near the conductor, which caused
some tingling, but it was safe to grab the conductor as long as they were
totally insulated from everything else (they used an insulated cradle
suspended from a crane).
   A few years ago we had a Galaxy 200ft hoist near Putney Bridge as one of
the radio link receiver points for the boat race. Just before the race
started a black cloud moved overhead and there was a single lightning strike
to the crane. There was no rain, and no warning. The crane was hurriedly
brought down to earth, the engineer who had been panning the aerial was
removed from the safety harness, dragged off, and sat on one side, and the
crane was sent back up with a replacement engineer to cover the race. The
original engineer was still sitting shaking long after the race ended, but
survived. We always put out a safety earth spike from every vehicle. The
lightning probably went mainly to the aerials, usually a 4 foot dish on a
heavy scaffold mounting plus a few dipoles. Standard practice now is that
safety comes first, and all personnel at risk should come down at the first
suggestion of lightning, even if the programme suffers.

-- 
Chris Bell


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