On Wed, 17 Mar 2004 21:33:43 GMT, Dave Shrader
wrote:

John Michael Williams wrote:

SNIP

However, the first radios transmitted
sparks, so in principle it should be possible to
transmit near a long wire separated by a small gap from
ground or another wire and get a small spark. So, I
decided to try an experiment.

SNIP

There is one other potential source for a spark that you did not
investigate.

A make/break contact in a switch causes sparks when opened. The US
Military specifies special shielded switches for their explosive, gas
vapor, etc., environments.

This reminds me of a story... (pause while room clears out).
Years ago I was an engineering student working for Cadillac
Motor Car. Electronic fuel injection was new then, and there
had been a couple of fires in the field that were suspected to
have been caused by leaky fuel lines, which were at higher
pressure than on the old carbureted cars. There were competing
theories, however, as to what exactly was setting off the fire.
I got assigned to help the guy doing the experiments to find out.

He had a car fitted with a plexiglas hood, topped by a small tower
with a high-speed movie camera pointing down for a good look
at anything happening in the engine compartment. Two fire
extinguishers were arranged to cover the under-hood area,
and a fuel vapor sensor was also installed there. The way
it was supposed to work was that he would drive and I would
operate the hand-pumped sensor, and at the first sign of fire
he would trigger the extinguishers. We ran all the tests
at the GM Proving Grounds in Milford, Michigan.

We tried making leaks in the fuel injection hoses. We had gas
spraying all over under the hood, collecting in pools on the
hot exhaust manifold. We tried poking holes in the spark
plug wire insulation. Nothing, no fire.

Finally I got a bright idea, and loosened the ground for the
air conditioner compressor clutch. The idea was that this
was a big inductor, and if the circuit opened there would
be a big spark. Then all we needed to do was get the
wire to bounce. We tried swerving from side to side,
and driving on bumpy tracks, but no deal. I was *sure*
that this spark would do the job, but we couldn't tell
if we were really getting the spark. So finally I stood on the
hood, holding on to the camera tower, so I could see
for myself if there were sparks. He drove down the
bumpy road one more time, and I did in fact see a spark:
The high-speed movie shows the fire spreading out
from it, more and more on each frame. Also on each
frame was the back of my head, moving away more
and more on each frame, until the extinguishers doused
everything. What a rush!

Them was the good ole' days.....


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com