Conference 7.286::home_work

The basis of the controversy is the effect of low-frequency magnetic
fields on the human body.  The studies have been done several times
with some groups claiming a strong correlation between some types of
cancer and living near power distribution lines. (You know, the big
towers with the mega-cables strung between them.)  Previously the
studies had been dismissed, but the most recent set have even the
conservative types thinking there might be something to it.

Enter the thinking that if a lot is bad a little must also be bad. 
Some people are concerned that the effect of a low powered, low
frequency field right next to you might be the same as a high  powered
low frequency field that is a block away.  I don't claim to know one
way or the other, I've never done nor seen field strength figures for
these instances.  Anyway, the place an electric field is *closest* to
you is when you're sleeping under an electric blanket that uses AC to
heat the coil. (I understand there are DC models as well that are not
being touted as bad.)

The argument about unplugging the blanket has to do with the fact that
the switch generally turns off just one leg of the power. (same as your
light switch -- the switch is on the "hot" side.)  The fear is that you
still get the 60-cycle field effect from the remaining wire.  I'm not
sure this has a lot of merit.  I would expect the field strength would
not be much more than you get being in a room with wiring all around you.

In all cases, the strength of the field drops off rapidly as you
increase your distance from it. (double the distance, the power is cut
four times.) So your body should get a much weaker field from a
baseboard four feet away than a blanket that is right on top of you.

I don't believe there are any studies that are accepted as having
proven a relationship between electric blankets and ill health.  The
studies that are accepted concern people living near (under) power
lines.  They have shown that what we thought was a safe dose before was
probably off by a few orders of magnitude.  You have to draw your own
conclusions from there. 

                           >>>==>PStJTT

There's no current flowing in an electric blanket that is switched off.
The electrons don't "go looking for somewhere to go".

			Steve

    Well, my grandmother slept under an electric blanket for years and
    she lived to be 91, so I wouldn't worry too much.  (Yeah, I know,
    if she *hadn't* slept under an electric blanket she'd be 119 by now.)
    
    That business about the "electrons looking for someplace to go" when
    the switch is off is totally ridiculous.  Given that the proponents
    of this theory are saying things like that, I have rather serious
    doubts about anything else they may be saying.
    
    The BIG high-tension power lines are DC, I believe.

    Well, there may be an electric field around blanket that's switched
    off, but the problem {appears to be, may be, may not be} magnetic
    fields, which are not present when the blanket is turned off.
    
    Willie

    re: .3
    
    The big power lines are 220,000 volts AC, DC doesn't do well over
    long distances, that's why AC is used.
    
    Fred

re .5:

There are now some high voltage DC power lines, and some more are being
installed.  They can be more efficient than AC lines, especially when shipping
power over very long distances.  They have completed building a �450,000 volt
DC power line that brings hydroelectric power from Quebec through New Hampshire
to a substation in Ayer, MA and are testing it now.  Since this is new
technology, these lines are still pretty scarce.  Most of the BIG power lines
now in use are 220,000, 345,000 or sometimes 765,000 volts AC.

-Mike

    There was a "news" show on WTBS, channel 17, called "Earth Watch" or
    something enviornmentally sounding last night.  The subject they were
    touting last night was electromagnetic fields set up by electrical
    stuff and the dangers to people.
    
    They were measuring the fields with a meter and it was calibrated in
    Guasses(sp?).  Supposedly 2 Guasses was the dividing line and greater
    than 2 was considered a harmful level.  They had this guy wandering all
    over this test subjects house saying that everything was bad and that
    their childern were more likely to develop lukemia.
    
    For instance, the digital alarm clock created an electromagnetic field
    which was higher than 2 guasses within in 2 ft of it.  The expert
    suggested they move if off the headboard and on to the night stand so
    it would not contaminate their heads all night long.  The water bed
    heater should be turned off at night while sleeping because it sets up
    a field and the water helps to intensive it by reverberating the field.
    
    They lived under the huge power lines.   They finally said that this
    house was no worse than any other "normal" house except for the power
    lines.  They suggested that you take precautions like don't stand in
    front of your microwave while it is cooking, don't sit close to the TV,
    and move your alarm clock.
    
    They scared the people enough that they plan to move.

I assume the 2 Gausses (measure of magnetic flux density) off the alarm
clock included the background level from the overhead powerlines?  I
had a chance to hear Wayne Greene, noted crackpot of the ham radio
world, talk last weekend and he is claiming that levels in the range of
a couple of hundred milli-Gauss are harmful and is waging war on
"killer blankets" as he calls them.

I'm willing to believe there is more to it than we thought a few years
ago, but I am unwilling to believe that more people are dying from
electric blankets than AIDS or automobiles.  A beneficial side-effect
if there's enough of an outcry on the subject will be better shielding
of electrical devices.  But usually the benefits of government
intervention carry a high cost, and I'm not sure I'm looking forward to it.

                              >>>==>PStJTT

    I bet that gauss meter would wrap its silly pointer around its peg
    if they turned it on in my office.
    
    	- Vick (I've moved the VSII box from between my legs) Bennison
    
    

    If you're going to sleep under an electric blanket, you can strap an
    aluminum pie plate to your butt and head to shield these most sensitive
    parts of the anatomy.  Replace the plate when it begins to glow.

    .10:
    
    No need to replace it -- just take a set of jumper cables and carefully 
    hook up one end to the aluminum pie plate, after you have hooked the
    other to the breaker box's ground stake, or to the water pipe coming
    into the house.  If you use the water pipe, though, be sure to avoid
    grounding through the water meter;  it's not good for the meter, and if
    you have one of those remote readout thingies (like in Billerica) it
    will never read right again...
    
    Dick

    
    Make sure you isolate your alternate energy guinea pig before
    degaussing the pie plates (replacement parts are hard to get).
    

I have a problem.  I am exposed to second hand magnetic fields.  My wife 
keeps the heat in the bedroom (fortunately on a separate heating zone :-) 
at 75+.  AND uses an electric blanket.  I am in the same bed sweating with 
just the sheet.  Meanwhile, I am exposed to all those magnetic effects.

BTW, don't you have to use a magnetic material to shield from magnetic
fields?  The aluminum pie plates will only shield against the eletric
fields.  (If I remember my E&M correctly)

BTW, in the near field of a long conductor the effects drop off as 1/r. 
From a point source like an alarm clock they drop off as 1/r**2.  Does
anybody remember the math for the near filed of a plane (or blanket)?

Stan

  The field falls off as 1/1. For a planar source, there's no
  attenuation of the field at all until you get out of the near field,
  which extends to approx 1/2 the diameter of the planar source measured
  from its center. Full strength radiation. You're a dead man. I can't
  even understand how you managed to enter the last reply :-).

    What we need is mu-metal for magnetic screening, not aluminium.
    
    There are an awful lot of dead people out there if em fields are
    very dangerous.
    
    Moreover, people who live in un-electrified houses should live longer
    than we do, all other things being equal.  Given that all other things
    are rarely equal, general life expectancies don't seem any better for
    us than those of our predecessors.
    
    Other comparisons ... in the UK and Europe, they use higher voltages
    and hence higher E fields and consequently they have lower currents
    typically (given that they use a similar total power to us ... which
    is not true ... they typically use much less ... but anyway) and hence
    lower M fields.  They have no significantly higher or lower life
    expectancy than North Americans that cannot be explained other ways.
    
    So, I would put tend to believe that at normal domestic field strengths
    (e and m) there is little risk.
    
    Stuart

Re: .15 People in un-elctrified houses

Intuitively you'd think they'd live longer, but I think they actually
have a shorter life span 'cause they fall down stairs and break their
necks when they get up in the middle of the night to raid the icebox
(and we're talking *real* ice here...) 'cause they can't flip on the
light.  They also have higher mortality because, if they make it to the
icebox, there's no telltale fridge light to give them away, and so they
stand there longer and eat more of the things that are bad for them and
have heart attacks.

                        >>>==>PStJTT

    a large percentage fall to fatality from frustrated fraus who find
    feces from fathers who fail to find the front of the john and fixate on
    faucets instead.  
    
    fred
    (alias tony)

    I'm gonna die twice as fast as most people 'cause I sleep with an
    electric blanket AND electric mattress pad.  The mattress pad is used
    to make the bed toasty warm and then shut off, but seeing as how these
    things emit death rays even when turned off I guess I should write my
    obituary before it's too late.  :-)

    -Bob

    
    Instead of electric blankets, why not use a nice fluffy down comforter
    instead?  If you can, have a friend in Europe buy one there on their
    way over here; you get more down for less money on the other side of
    the pond.
    
    CQ