Changing the subject line would be a VERY good idea as there is still 
useful stuff running in parallel on the original subject.

>> > The 'OMG electrical radiation' crowd like to bring up a study 
>> > that
>> > found preganant women who used electric blankets miscarried more.

Anyone who doesn't like to "bring up" and competent study that 
produces a statistically significant increase in miscarriage rate 
would be a fool. This shouldn't be a competirion - it should be about 
finding out about reality.

The following uses the terms 'electricity', 'of course', and 'simply' 
as perjoratives. Such an approach risks creating a minset that will 
cause us to overlook real hazards, whatever they may be.

>> > They blame electricity, of course,
>> > when it was simply that the women
>> > were getting too hot.

It may well be that the study was badly designed and that 
retrospectively obvious confounding factors were the primary causal 
agent. Or not.

Test:

This MAY not work on the 10th floor of a pure glass house on a hot dry 
day in a desert, but in a typical NZ house it works just fine.

Turn on an electric blanket on a bed and have someone lie on the bed 
on top of the blanket.
Blanket can be on any setting but high is probably slightly better as 
more wiring involved (see below).
Stand next to the bed and rub fingertips with the person on the bed.
Note the mild continuous "electric shock" which can be felt. Not 
painful but very discernible. A rough "burring" effect at the 
fingertips.

What is happening is that the blanket is capacitively coupling mains 
voltage via them to you and via your body capacitance to local ground. 
(My comment about the 'glass house' notes that the final return path 
may be via return distributed resistance. The precise mechanism is not 
crucial to the basic demonstration).

Body capacitance to the blanket is probably 100's of pF and from body 
to ground is highly variable and lower. It's entirely possible that 
there is no deleterious effect from acting as a capacitor plate for 
mains leakage in this manner. But, in the absence of at least 
statistical indications to the contrary, if this didn't make you at 
least uncertain about the possible effects of such an environment on 
pregnant women then I'd be just a little surprised.

In such cases a little care in rejecting outrageous claims can 
*sometimes* produce dividends. When the returns on invested effort get 
too low we start to get blase about the whole idea of incipient 
hazards. Every now and then a Thalidomide or similar reaches out to 
jog our sensitivities.



                Russell 

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