Re: Meeting with Speedrail

[James Robinson <NOSPAM@ERIE.NET>]

Ron Bennell wrote:
> 
> I believe that you around confusing magnetic fields, electric fields and
> electro-magnetic fields.
> 
> AFAIK electro-magnetic fields (radio) affect humans,  and electric fields
> (around high voltage power lines) are speculated to have some effect on
> humans. The possible affect of magnetic fields (around current carrying
> wires) tend to upset electronic equipment more than people.

This was my point.  Radio waves and the fields around power carrying
wires are both forms of electro-magnetic radiation.  The difference is
in the frequency of the wave.  In the case of radio, the frequencies are
typically higher than common power transmission lines, and it is
generally accepted that the higher the frequency, the greater the risk
to humans. A microwave oven is a manifestation of the effect of some of
the highest frequencies we normally harness, and high frequency gamma
radiation is well known to be damaging to humans.  

Along the same theme, there is also great concern about the long term
effect of mobile phones, since they tend to operate at the highest
frequencies of any common radio broadcast, and the antennae are
typically right beside the user's head when the phone is in use.  The
technology has not been around long enough to see if there will be will
be a long-term problem.

In the case of high voltage power lines, the extra wattage of the
radiated power may make up for the lack of high frequency, and may also
have a detrimental effect on humans.  Whether the lower frequency, and
high power electro-magnetic radiation of power transmission lines has an
effect on humans is still controversial.

Looking at magnetic levitation vehicles, the concern is similar to that
of power transmission lines:  High powered magnetic radiation at low
frequencies.  There is no common agreement on the effect on humans, but
those who wish to err on the side of caution are waving flags about in
warning.

> 
> A Faraday cage will protect against electric fields, EM fields (radio) may
> be reduced, but usually magnetic fields to pass straight through.

EM fields are reduced inside a Faraday Cage.  That is why radio testing
and servicing labs are placed inside grounded metal boxes: to eliminate
stray radio signals in the test area.  It is also why a hand-held GPS
receiver won't work inside an aircraft, unless held near the windows.

With the introduction of AC power on locomotives, there was concern
about the effect of the EM radiated by the electrical system. This
ranges from the power generated at the alternator, through the power
inverter system, to the use of the power at the traction motors.  The
people occupying the locomotive operators' cab would in effect be
sitting on a large electrical generating and transmission system, and
the effect of the low frequency EM waves, on humans, was brought up as a
concern.

A number of tests were therefore carried out to measure the strength of
the EM radiation in the operators' cab.  The results of the tests showed
that the operators would be exposed to less radiation inside the cab
than you or I would normally be exposed to in our normal lives.  The
effect of the steel box that the operators sit in is to reduce the
radiation to a level that is below that of background radiation.  Thus,
the logic suggests that even if high power, low frequency radiation has
an effect on people, those occupying locomotive cabs are at very low
risk since they will be exposed to less radiation that a farmer working
in the fields well away from any artificial source.

Again, looking at maglev, the metal structure of the vehicle should
significantly reduce the exposure of the occupants to high intensity EM
radiation.  If the vehicle is not made of metal it is a different story.