Direct and indirect evidence suggests that AC electric
and magnetic fields increase the risk of certain cancers and other
physiological and psychological abnormalities. Although how this happens is
not fully understood, both magnetic and electric AC fields that surround the
body can produce AC electric current inside the body. The best available
theory is that this current interferes with the normal transport of ions
across cell membranes. (1)
At a continuous exposure of
about one billionth of an amp of AC current per square centimeter (give or
take a factor of three), biological effects begin to be observed. Very
preliminary results show that at five times that level, for example, an
increase in protein production in cancer cells is seen; but when the field is
increased 1000 times further, the increase in protein production is only three
times greater (not 1000 times greater). These changes are seen for AC current
at several different frequencies, including 60 Hz (60 oscillations per
second). (2)
If the
cell-membrane-interference theory is correct, the body should be sensitive to
current at any frequency up to about 1000 Hz (the exact upper limit frequency
is not known and experimental measurement of it has not been attempted).
Based on the above evidence
and some epidemiological studies, (3) it would be prudent to avoid continuous
exposure to any electromagnetic pollution that produces AC current inside the
body higher than one billionth amp per square centimeter, at frequencies of
1000 Hz or below. (No absolute hazard threshold has been established yet, but
the lower limit for biological effects is probably between one-third and three
times that level). Preliminary results suggest also that it's better to spend
a short time well above this threshold than a long time just above it.) At
frequencies above 1000Hz, the body is likely also to be sensitive, but not as
sensitive as it is to lower-frequency currents.
An external magnetic field
of 3 milligauss or an electric field of 2.5 kilovolts/meter at 60 Hz will
produce approximately one billionth amp per square centimeter. The current
produced inside the body is proportional to field strength times frequency, so
at 120 Hz (twice the frequency), only half as much field (i.e., 1.5 milligauss
and 1.25 kilo-volts/meter respectively) is required to produce the same
current inside the body. Interestingly, a fairly strong magnetic field (500
milligauss) and electric field (about 2 kilovolts/meter) exist in nature, but
these fields are static, and thus have a frequency of zero - they produce no
current inside the body.
Therefore, an
electromagnetic pollution meter should be frequency weighted, meaning that it
reads the product of magnetic field strength times frequency and/or electric
field strength times frequency, if it is to gauge whether the electric current
inside the body exceeds a threshold level. This frequency-weighting should
extend up to about 1000 Hz and then the meter sensitivity should decrease at
higher frequencies.
Magnetic and electric
fields are vector quantities. This means they are specified as having a
magnitude (or field strength, measured in milligauss or kilovolts/meter
respectively) as well as a direction (an "arrow" showing which way
they are pointing). The effect on the body is more or less independent of the
direction of the field; only the magnitude is important. Virtually all field
meters read the field strength in one direction only. The sensor of these
meters must be pointed in the same direction as the field happens to be
pointing; otherwise the meter will read less than the true magnitude of the
field strength. If the sensor is pointed perpendicular to the local field
direction, the meter will read zero, no matter how strong the field is. Then
it will completely miss the field. To avoid this inaccuracy, a meter should
read the true magnitude of the field, so a user could walk through a room with
a meter and get an accurate, immediate reading of the field magnitude at every
point along the path, regardless of which way the meter is oriented.
This TriField meter
combines all the features needed for fast, accurate screening of
electromagnetic pollution. It independently measures electric field and
magnetic field and is properly scaled for both, to indicate the full magnitude
of currents produced by each type of field inside the body. As a result, it
"sees" much more than any other electromagnetic pollution meter.
Depending on where the knob is set, it detects either frequency-weighted
magnetic fields (two separate scales) or frequency-weighted electric fields in
the ELF and VLF range (it has significant sensitivity at 100,000 Hz, well past
the 17,000 Hz horizontal scan of video displays). It also has a setting which
lets you gauge radio wave power all the way up to three billion Hz (3 GHz),
which includes home microwaves (2 GHz), CB and cellular phone equipment, and
many radars.
This TriField meter is also
the only one which combines magnetic, electric, and radio/microwave detectors
in one package, so the entire non-ionizing* electromagnetic pollution spectrum
is covered. In addition, the magnetic setting and the electric setting measure
true magnitude, a feature found elsewhere only in very expensive meters. If
you hold the meter in the center of a room and tip it to various angles, the
magnetic reading will stay approximately the same (+/- 15% typical) regardless
of which way you tip or rotate it. The electric reading is similar, although
the presence of your body alters the actual electric field, so readings will
vary more. The radio/microwave setting reads full power radiated into the
front of the meter.
Surprisingly, the TriField
meter is one of the least expensive meters available. The few other meters
below $200 read only low-frequency magnetic fields and only one direction (not
true magnitude). The magnetic section of the TriField meter has three
field-detecting coils pointing in the X, Y, and Z directions. A circuit
amplifies these signals and gives them the proper frequency-weighting
(sensitivity increases linearly from 30 Hz to 500 Hz, it stays level to 2000
Hz, then it falls off slowly to near zero at 100,000 Hz, but with some
residual sensitivity up to 100 MHz). A unique network combines the three coil
outputs non-linearly to approximate a true magnitude. The meter is sensitive
from .2 to 100 milligauss full scale at 60 Hz (or .1 to 50 milligauss full
scale at 120 Hz, etc.) with a resolution of .2 milligauss in the sensitive
range. Accuracy is +/-20% at mid-range.
In most homes and offices,
a large fraction of the total magnetic field is at frequencies above 60 Hz. A
TriField meter, when exposed to a 3 milligauss field, will read "3"
if the frequency of the field is 60 Hz, but it will read "6" if the
3 milligauss field is at 120 Hz. In contrast, a non-frequency-weighted meter
will read "3" in both cases, and a 60 Hz-only meter will read
"3" and "0" respectively (even though in the 120 Hz case,
the current induced in the body is twice as much.) This underscores a problem
with present epidemiological studies of magnetic field health effects:
generally, non-frequency-weighted meters (or even 60 Hz-only meters) were
used. Indications are that in homes where these meters read consistently above
3 milligauss,§ the chance of developing certain cancers is increased.
Depending on the distribution of frequencies (which was not recorded in the
studies), a TriField meter would generally read between "3" and
"9" if the other meters read "3". Consequently, the
threshold for the TriField might be more appropriately placed as high as
"9" milligauss, with the uncertainty arising because previous
studies did not measure frequencies above 60 Hz in a standard or uniform way.
The electric section
consists of four metal plates under the meter face. Because the meter housing
is plastic, the electric fields can go through to the plates, which are also
arranged to detect AC electric fields in the X, Y, and Z directions. Circuitry
similar to the magnetic section converts the signals into an electric field
signal which is frequency-weighted. Sensitivity is .5-100 kilovolts per meter
at 60 Hz, with resolution of .5 kilovolt/meter. Accuracy at mid-range is
+/-30%.
Radio and microwaves are
composed of a particular combination of electric fields and magnetic fields
that is self-sustaining. For frequencies below about 100 MHz (100 million Hz)
the principle effect on the human body is from the magnetic field part only.
This is because the electric field component of radio waves produces much
weaker currents in the body than does the magnetic field unless the wavelength
of the waves is smaller than the height of the body. Low-frequency electric
fields by themselves can be strong enough to create significant current, but
only if they are from sources other than radio waves.
The radio/microwave section
has a small L-shaped antenna in the front. The signal is amplified and
converted to a power density magnitude, calibrated at typical home microwave
oven frequency (2 GHz). It reads 0 to 1 milliwatt/square centimeter. The
resolution in the low range is .01 mW/cm2, which is the Russian standard for
maximum safe microwave exposure to avoid changes in brain activity, (4) and is
the most conservative standard of any country. (The new OSHA safety threshold,
as of 1-1-93 is 1 mW/cm2, down from the previous 10 mW/cm2). Typical accuracy
is within a factor of two. Variations are caused by reflections off the user's
hand and body.
A knob on the front has six
positions: OFF, BATTERY TEST, two MAGNETIC field sensitivities (.5-100
milligauss at 60 Hz, and .2-3 milligauss at 60 Hz, to measure low fields more
accurately), ELECTRIC field and RADIO/MICROWAVE power density. The meter face
is analog (needle type). A needle reading of one-third of full scale
corresponds to either .6 milligauss or 3 milligauss @ 60 Hz, 3 kilovolts/meter
@ 60 Hz, or .04 mW/cm2 respectively in the magnetic, electric, or
radio/microwave field settings. Long-term personal exposure to levels higher
than these should be avoided, so the meter is labeled "HIGH", above
these levels. Unfortunately, because of uncertainty of population studies, the
true health-effect threshold may be as low as 1 milligauss or as high as 10
milligauss.
In most homes or offices,
some areas are "hot" spots with readings in the HIGH range. Most
often, this is caused by magnetic fields, which come largely from unpaired
internal wiring. (Contrary to popular belief, outside power transmission lines
and transformers do not generally contribute as much magnetic field as does
internal wiring.) Other magnetic sources include video displays, motorized
clocks and other equipment, electric blankets and heaters, fluorescent lights
and light dimmers, and the transformers that are inside consumer devices. Many
of the effects are from frequencies that are harmonics or multiples of 60 Hz
(120 Hz, 180 Hz, etc.) and 17,000 Hz of video displays. Magnetic fields are
difficult to shield, and either sheets made of specialized metal, or
electronic instruments which actively produce magnetic fields to counter
ambient fields, are required.
A few areas in most homes
read HIGH in the electric field setting. These include areas near improperly
grounded equipment, the front of video screens, and fluorescent lights. Most
of these fields are at 60 Hz. Unlike magnetic fields, electric fields can be
easily shielded using a grounded metal screen or foil; VDT screens of this
type are readily available. You can greatly reduce the strength of an electric
field just by placing your hand in front of the source. This effect can be
seen using a TriField meter.
Occasionally, certain areas
read HIGH in the radio/microwave setting. These include door seals around
microwave ovens, and cellular phones (but not regular radio phones, which are
very low-power). Radio/microwaves can be shielded in the same way as electric
fields, although the lower frequency radio waves are not shielded by your hand
as easily as microwaves are. (Metal screens will shield both.) In the U.S.,
radars and FM transmitters can legally expose residents to moderately high
power levels, but such exposure is not common.
By seeing "hot"
spots in your home or office, you can move furniture, cribs, or beds to reduce
exposure. You can also take corrective action to avoid long term exposure to
appliances that emit high electromagnetic pollution levels. If you have
unusual sensitivity to a particular type of field, you can identify where
problems exist (e.g., wearers of pacemakers should avoid even brief exposure
to high radio/microwave power levels. Some anecdotal evidence indicates that
brief exposure to very high AC electric or magnetic fields may cause
nervousness or seizures in some people.)
The TriField meter comes
with a one-year limited warranty and a 9-volt transistor battery included.
This type of battery lasts about 10 hours (total measurement time). When the
BATTERY TEST reads low, it can be replaced with any rectangular 9 volt
transistor or alkaline (which lasts about 50 hours) type.
The meter is manufactured
in the USA. TriField is a registered trademark of W.B. Lee.
References
(1) EPA Draft report March 1990. See Nature, vol. 345,
June 7, 1990, p. 463.
(2) Science News, vol.137, no.15, April 14, 1990, p. 229. This assumes average
body resistivity of 150 ohm-cm.
(3) Several studies are in the literature. For example, The Lancet, January
29, 1983, p. 246; New England Journal of Medicine, vol. 307, no.4, July 22,
1982, p.249.
(4) See The New Yorker, June 12, 1989, p. 69; and Cancer Research, August,
1988, p. 4222.
(5) In a study of about 500,000 people, continuous exposure to 2 mG (at 50 Hz
in Europe) correlated to a 2.7-fold increase in childhood leukemia rate. See
New Scientist, October 31, 1992, p. 4. * "Non-ionizing," because
this meter does not read nuclear radiation. § A new Swedish study suggests l
mG is a better safety threshold. (5)
TriField(r)
Meter
Instructions
ALPHALAB INC.
TriField is a registered Trademark of W. B. Lee.
TAKING READINGS
Hold the meter as shown.
This prevents your hand from shielding electric fields or microwaves. (Your
hand cannot shield magnetic fields.) Read the top scale when the knob is set
on "MAGNETIC (0-100 range)", or on "ELECTRIC". This top
scale reads 0-100 milligauss when on "MAGNETIC (0-100 range)", or
0-100 kilovolts per meter when on "ELECTRIC". For more sensitivity
to weak magnetic fields, set knob on "MAGNETIC (0-3 range)", and
read the center scale. When the knob is turned to "RADIO/MICROWAVE",
use the bottom scale (.01-1 milliwatt per square centimeter) and point the
meter toward the radio/microwave source.
Avoid long term personal
exposure to HIGH (red scale) readings in any setting; they pose a possible
(but not yet certain) health risk. The dotted red scale is borderline
exposure, and probably poses little if any health risk. Below that is
generally regarded as safe for continuous exposure.
BATTERY TEST
Switch the knob to
"Battery Test". If the battery needs replacement, the needle will be
to the left of the line that is itself left of the words "Batt.
Test".
CALIBRATION
The ELECTRIC and
RADIO/MICRO-WAVE settings should be low (below the dotted red scale) in most
parts of homes or offices, especially if you cup your hand in front of the
meter or place the meter in a metal box. In the country, far from power lines,
the magnetic field should also read very low (below .2 milligauss).
High Magnetic Field Sources
Hold the meter near these
sources, and set the knob on "MAGNETIC (0100 range)." Some of these
should read greater than 10 milligauss on the top scale. Your body or hand
does not shield these.
·
AC wall adaptors
·
Vacuum cleaner or motorized equipment
·
TV screens
·
Motorized clocks (120 Volt)
·
Lightning
·
Inside of commercial jets
·
Running cars, especially near front floorboard
If you can't get a reading
greater than 10, test the battery. (If the battery is bad, the meter needle
cannot go up to full scale.)
High Electric Field Sources
Switch the knob to
ELECTRIC. If you point the top surface of the meter box (the surface furthest
from your hand) toward these sources, some should read greater than 3
kilovolts per meter. (Notice that your body can easily shield electric fields;
the reading is lower if you cover the top surface of the meter with your hand.
Also, the presence of your hand at the back of the meter compresses the
electric field, making it read somewhat higher than if the meter were held in
that position hanging by a string.)
·
TV screens
·
Improperly grounded electrical equipment
·
Single "hot" wire, even if insulated
·
Fluorescent lights
·
Electric Blankets, when plugged in, but "off",
especially if the AC plug polarity is reversed
High Radio/Microwave Power
Sources
Switch to RADIO/MICROWAVE
and point the top (front) of the meter toward the following sources. Read the
bottom scale. Your hand can shield the higher frequencies (microwave) but not
lower frequencies.
·
Cellular phone*
·
CB or amateur radio transmitter*
·
Microwave ovens near door seal. A reading of more than .2 mW/cm2
(needle halfway up) at a distance of six feet suggests a leaking microwave
door seal, which should be repaired.
·
Will also produce electric and magnetic field readings. An ordinary
radio phone however, will produce little or no needle deflection.
CHANGING THE BATTERY
The battery is a 9-volt
rectangular type. The alkaline type will last about 30 hours of continuous
use, while the transistor type will last about 10 hours. Turn the meter OFF,
unscrew the back (four screws) and slowly separate the back cover. DO NOT PULL
APART RAPIDLY - it may break the wires. Disconnect the battery and slide it
out by pushing it out from the back. Then replace it. Reconnect the new
battery and reassemble. Leave the meter OFF when not in use; even
"Battery Test" will draw some power.
SPECIFICATIONS
The MAGNETIC and ELECTRIC
field settings are frequency-weighted from 30 to 500 Hz and are calibrated at
60 Hz. For example, a 60 Hz magnetic field with a strength of 2 milligauss
will read "2" on the meter, but 120Hz at 2 milligauss will read
"4" on the meter. This is to gauge the currents induced inside the
body, which are proportional to field strength multiplied by frequency. From
500Hz to 1000Hz, the response is flat +/-20%. Above 1000 Hz, the magnetic and
electric sensitivities of the meter slowly decrease with increasing frequency,
falling to zero near 100 KHz, but with some residual sensitivity up to 100
MHz. In theory, the body's sensitivity to fields should begin to decrease at
frequencies above about 500 Hz. Accuracy is +/-20% of scale reading for
MAGNETIC, and +/-30% for ELECTRIC (RMS @ 60 Hz).
RADIO/MICROWAVE is
sensitive from 50MHz to 3 GHz and is calibrated at home microwave oven
frequency (2 GHz). The accuracy is -50% to +100% because of the unpredictable
effect of reflections within the room and off the user.
WARRANTY
The unit is warranted
against defects in materials and assembly for one year from the date of
purchase. Customer should return defective unit, shipping prepaid, for repair
or replacement.
DISCLAIMER
Use of the meter is solely
at the user's discretion to identify personal exposure to non-ionizing
electromagnetism of the strength and types believed (as of May 1992) to pose a
possible health risk. Because a meter of this type may malfunction, the user's
responsibility is to determine if the meter is working properly by using it to
measure a known reference (see CALIBRATION section of this booklet).
Manufacturer or dealer cannot assume responsibility for damages resulting
either from a defective meter (except to replace or repair said meter within
the warranty period) or from inaccuracies in the present body of knowledge
concerning the health hazards of electromagnetism.
The meter should be used so
that simple steps (such as moving furniture) can be taken to reduce relative
exposure within a home or office. If more drastic actions are contemplated,
remember that some readings in the HIGH (red) zone may ultimately prove not to
pose a health risk, so consult expert advice before taking more drastic steps,
and perform independent tests with another type of meter. Remember that the
TriField(r) meter is frequency-weighted, so in most environments, it will read
higher in the magnetic field setting than a more traditional meter of the type
used in epidemiological studies to set possible hazard thresholds
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