From: ornitz@kodak.kodak.com (Barry Ornitz)
Newsgroups: sci.med
Subject: Re: ******** MICROWAVE HAZARDS ******* [Pacemakers]
Summary: I wish people really understood how microwave ovens worked!
Keywords: microwaves, radiation, leakage, interlocks
Date: 26 Aug 92 00:34:19 GMT
Followup-To: sci.med
Organization: Eastman Kodak Company, Eastman Chemical Company Research Labs

I wish I had time to take this apart, piece by piece, and correct all of the
erroneous information.  Unfortunately, emergency family business will keep
me away from the network for at least a week.  If anyone wants to be kind and
mail me any ensuing discussion, I would be grateful.

In article <1992Aug24.235158.7965@gateway.novell.com> 
terry@thisbe.npd.Novell.COM (Terry Lambert) writes:
>	[ ... Barry goes on to point out that the primary danger is from the
>	      magnetron, and says that the danger is always present due to the
>	      permanent magnets therein ... ]
>
>Testing the "Magic Chef" with real equipment reveals that it, indeed, does not
>have enough leakage to pose a serious threat, and that there is a permanent
>magnet in it.  However, the amount of induced current in a probe perpendicular
>to the magnetic field is (as expected) much higher when the oven is on. I posit
>that induced current is the real danger to a pacemaker wearer, since the amount
>of current induced is significant compared to the amount of current a pacemaker
>from it's documentation, delivers to stimulate the bundle of Hiss.

Just what is being measured here?  The magnetic field at low frequencies or the
electromagnetic field at 2450 GHz?  Microwave leakage from a home oven would
generally not be polarized due to the effects of the multimode cavity and the
"stirrer".  If you are talking transformer leakage, pacemaker wearers should
certainly avoid home audio systems too!


>I also stated that lower frequency and "line frequency"(60Hz in the US)computer
>mointors make approximately the same "whine" when they are on as a microwave, and
>that since I can't stand the noise, in any case, this would cause me to keep a
>"safe" distance away.  I was attempting to imply that, even were microwave ovens
>dangerous, EM fields fall off by the inverse cube of the distance (I stupidly
>said "inverse square" when all I meant to imply was a geometric relationship)
>and therefore, if you were worried about getting "zapped", so to speak, keeping
>a short distance away would be sufficient, even if there were a real danger.
>
>You could, of course, keep a family member with a pacemaker close to the oven to
>detect leaks, since they will be at least as sensitive a detector as someone
>without a pacemaker, and potentially a better one if the lead happens to be a
>dipole whose resonant frequency is close to that of the microwave.  This is
>not a suggested practice... get a canary with a pacemaker instead.  8-).

The whine is generally much higher pitched that 60 Hz.  You are hearing
transformer buzz and harmonics caused by the non-sinusoidal waveform.  It is
the inverse square law, however.

Not being a physician, I do not know the typical depth to which a pacemaker is
implanted.  I would guess it is below the typical penetration depth of a home
microwave oven. [Yes, microwaves do NOT heat from within.  Penetration depth is
highly dependent on the material being heated. (more later!)  For lean beef, it
is only slightly over an inch.]


>I suspect that the magnetic danger is not one of "tuning" the pacemaker (the
>original magnetically "tuned" pacemakers were high/low rate toggle based on
>a hall-effect sensor, if my grandfather is correct about his), since the worst
>that could happen is a switch from high to low or low to high "gear" in the
>presence of a magnetic field similar to the one put out by the small permanent
>magnet on his digital watch band.  Instead, it is the one recently discussed
>here, which is that of anyone with potentially ferrous implants which can be
>affected by magnetic fields.  NMR (or MRI) devices put out enough of a magnetic
>field to pull small pieces of metal from high school metal shop through your
>optic nerve, as happened to one poster.  Moving an implanted prosthetic around
>in someone could be bad.  Also, there is the potential for a rather large
>induced current when the field is collapsed.

It is a mightly sad day when one of our NMR magnets' fields collapse.  There
was a story once about the cleaning lady who had her bucket pulled from her 
hand.  The bucket stayed on the side of the NMR for a week or so until the
factory repairman could arrive and re-align the instrument.


>One important point that Barry brought up was that microwave ovens do not put
>out ionizing radiation.  In laymans terms, microwave ovens are radio transmitters
>as opposed to bein radioactive.  Heating is accomplished by excitation of water
>molecules in the food.  Nearly no other molecules are excited, excepting those
>bumped by the hot water molecules.  This is the reason that popcorn kernels
>won't pop if you put them in by themselves.

Unfortuantely this is the point where Terry really shows his misunderstanding
of how microwave ovens work.  MICROWAVE OVENS ARE NOT BASED ON EXCITING
RESONANCE OF WATER MOLECULES.

Microwave ovens generate heat in many materials based on the dissipation
factor of the material.  The technical term is the imaginary component of the
complex permittivity.  Any material that has a significant loss or dissipation
factor at the microwave frequency will heat.  Water has a broadband high
dissipation factor which is nice because water heats easily in a microwave.
Ice has a much lower dissipation factor, and it barely heats in a microwave,
hence the special defrost cycles.

>None of this, however, answers the original posters question, which was "Am I in
>as much danger of cancer from my microwave as Trooper Joe is from his radar gun?"
>
>The answer is "no" and the reasons are many.  First off, radar guns don't use
>the same frequency as microwave ovens.  If radar guns excited water molecules
>as well as a microwave oven does, Trooper Joe would have learned pretty damned
>quick that pointing it at his lap while it was on was a bad idea.

It really gets bad here...
The original police radars operated at S-band, the same frequency range as
home microwave ovens, 2.45 GHz.  Later units operate at X-band, or 10.525 GHz.
Even newer police radars operate on the Ku-band or 24 GHz.  Water absorption
of microwaves is FAR higher at X-band than at S-band.  It is far higher still
at the Ku-band which is close to the lowest resonant frequency of water for
rotational (microwave) spectra [as opposed to vibrational (infrared) spectra].

>
>Many radar setups are also mounted permanently in the direction of travel and
>180 degrees from the direction of travel.  In order to "shoot" cars ahead of
>the officer, they shoot through the officers head.  This has caused the expected
>results in several officers, one of them here in Utah.  They certainly would be
>well aware of heating effects and left the things off if they were the same
>frequency.

See above.  Police radar units operate at power levels usually greater than
10,000 times lower than home microwave ovens.

>As Barry pointed out (omitted for space) in his posting, leakage is real low on
>most modern microwave ovens, both the several he tested, and the one I did
>after everyone started geting excited.
>
>All of this leads us to believe that operation of microwave ovens won't cause
>cancer as we have been led to believe that radar guns will... in other words,
>"the names "radar gun" and "radar range" are coincidental.

I have not been convinced that police radar guns really cause cancer.  As
others have pointed out, conclusive evidence in not yet in.  Statistics can
show relationships but they cannot show cause and effect.   As of now, I
consider the statistics showing a relationship between police and cancer
too poor to draw any conclusions from.

>Radar guns also have to have an unshielded "horn" to work, whereas microwave
>ovens are shielded boxes.
>
>If you are still concerned, stay in the other room after you have started your
>microwave, since distance should be an adequate countermeasure to any danger
>you believe is present.  Of course, you could just not buy ovens from the
>freight damage store, or avoid runing them while they are on your lap.  8-).

As I have pointed out before, the interlocks on home ovens are quite well
designed.  Damage severe enough to cause excessive seal leakage will be
quite obvious to the naked eye.  Part of the normal testing protocols involves
heavy blows to the door and seal assembly, and the oven must still be safe
to be certified.

>Now... anyone have any idea about the helth effects of the RF emissions from
>thos motion detectors that set your radar detectors off?

These Part 15 Field Distrurbance Sensors generally use even lower power levels
than police radars.  I once calculated you need to be within centimeters of
even high-powered sensors to come close to meeting the maximum allowable 
field strength limits.

>					Terry Lambert
>					terry_lambert@gateway.novell.com
>					terry@icarus.weber.edu

The above was not meant as a personal attack on Terry.  However, it is obvious
he has no understanding of how microwave ovens work and how materials
interact with electromagnetic fields.  It is regrettable that the public 
often bases their fear of electromagnetic radiation on such misinformation.

Many of the automobile magazines are playing up the cancer scare as a means
to get police departments to give up their radar.  I expect this effort will
backfire as police departments are going to "instant-on" radars to minimize
exposure, and to laser (lidar) systems.  Both of these make radar detectors
far less useful than they once might have been.

As I said in the beginning, I will not be reading any Usenet News for at
least a week, and our system does not hold articles for more than a day or so.
If anyone wishes to continue this discussion, please use direct email which
is kept.  Thanks.
					Barry
 -----------------
|  ___  ________  |       Dr. Barry L. Ornitz          WA4VZQ
| |  / /        | |       Eastman Kodak Company
| | / /         | |       Eastman Chemical Company Research Laboratories
| |< < K O D A K| |       Process Instrumentation Research Laboratory
| | \ \         | |       P. O. Box 1972, Building 167B
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