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Protecting/enhancing your Energy — Unique Environmental Energy Products for the 21st Century from The Energy Store |
All about EMFs 3 (cont’d) |
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CRT-STYLE VDTs A CRT-style VDT uses the same type of picture tube as a television set. The cathode ray tube is a large vacuum tube made of glass, and coated with phosphor on the inside. An electron gun shoots a beam of electrons from the back of the tube toward the front of the screen (i.e., toward the computer operator) until it hits the phosphor. The phosphor gives off visible light when it is excited by the electrons. A full screen image is comprised of thousands of dots, each one of which is refreshed (re-excited by a burst of electrons) between 50 and 80 times per second.
CRT-style VDTs give off all sorts of electromagnetic radiation: radio waves, infrared radiation (heat), visible light, ultraviolet light, microwaves, X-rays, ELF and VLF radiation. The radio waves are typically shielded with a layer of conductive material in order to meet the limits set by the Federal Communications Commission. The infrared radiation in the form of heat is not a health hazard, and of course the visible light is necessary in order to see the screen. The levels of ultraviolet light are substantially less than indoor fluorescent lights or outdoor sunlight, and the amount of microwaves is so small that it is almost undetectable. X-rays were once a problem, but strict guidelines in effect since 1970 have reduced the level of X-rays to less than what is naturally present in the environment. Most experts now agree that X-rays from CRT-style VDTs pose no problem unless the display is defective.
It is the ELF and VLF electromagnetic radiation from CRT-style VDTs which is presently raising concern. The ELF radiation (50 Hz to 80 Hz) comes from the vertical deflection coils, and the VLF radiation (15 kHz to 85 kHz) results from the horizontal deflection coils. CRT-style VDTs also have a power transformer which creates a 60 Hz field, and a flyback transformer which steps up the CRT's voltage to tens of thousands of volts and emits VLF electromagnetic radiation.
The levels of EMF emitted by a VDT can be quite high, but the measurements drop off rapidly with distance. That's why it is important to sit back at least an arm's length from the front of the screen. Measurements taken from a typical color VDT (a popular 13 inch color display was used for this test) show 37 mG of ELF at 6 inches, 12.6 mG at 12 inches and 4.5 mG at 20 inches. The VLF field (which contains several hundred times more energy than an ELF field at the same mG reading) is 6.3 mG at 6 inches, 2.0 mG at 12 inches, and .66 mG at 20 inches. At 6 to 7 feet the ELF level drops to background, but the VLF level is still measurable 10 feet away.
Because the EMF comes from the internal components, the EMF levels on the back and sides of a VDT are higher than in front, often by a factor of 2. This means you must distance yourself further away from the back and sides of a VDT (at least 3 to 4 feet, respectively) in order to achieve the same level of exposure. Smaller VDTs are not necessarily better, either. A 15 inch VDT might well generate a stronger magnetic field than a 21 inch one, because the field's strength depends more on the internal design of the deflection coils and electronic components than on the screen size.
The electric components of a VDT consist of an electrostatic potential and alternating electric fields at ELF, VLF and radio frequencies. The electrostatic potential results from a build-up of an electric charge on the surface of the screen. Its effect is similar to what most of us have experienced when we get a static shock by walking across a carpet and touching a metal object in a dry environment. This static may attract dust on your screen and cause eye irritation. On some occasions, skin irritations have been reported, although this is infrequent and the cause has not been proven. Fortunately, no long-term or serious health effects have been attributed to the electrostatic or alternating electric fields. Moreover, the electric fields can easily be blocked by incorporating a grounded conductive layer into an anti-glare shield.
On the other hand, ELF and VLF magnetic radiation is not easy to block. Low frequency magnetic fields can easily travel through layers of solid aluminum, copper or steel with little reduction in strength. Further, unlike an electric field which travels in a straight line, a magnetic field loops outward in curves, forming an irregular, rounded envelope of energy. Adding to the problem is the source of the EMF, which is not the front of the screen but the deflection coils, flyback transformer, and power supply inside the VDT. The EMF travels up and over the top of the screen, around the sides, and underneath in all directions.
"Screen savers" designed to blank out the screen after a short period of inactivity are useful to prevent "burn in" or damage to the VDT's phosphor coating from constant use, but even if the image is blank, the components which generate ELF and VLF emissions are still active. Similarly dimming the display will do nothing to reduce the fields. Shields placed in front of a VDT's screen do not block ELF magnetic fields. They do block electric fields, but the ELF magnetic field is the main concern.
Shielding with Mu metal Some well-meaning people, when they hear the word radiation, think that lead shielding is a solution. It isn't. Unlike X-rays, ELF and VLF magnetic fields can penetrate right through lead. One shielding method which has shown partial success is to install a Mu metal barrier around the deflection coils and flyback transformer inside the cabinet of the VDT. Mu metal is an alloy of nickel, iron, and various other trace metals which is magnetically permeable, meaning that it is a good conductor of magnetic lines of force. The percentage of each element in the Mu metal affects its performance, as does the thickness and the method of manufacture. While Mu metal can reduce magnetic radiation if installed properly, it cannot block all the radiation in the same way that lead blocks out X-rays.
Mu metal is not recommended as a do-it-yourself solution for several reasons. The configuration and placement of the Mu metal will vary with each different model of VDT, sometimes requiring many hours of experimentation to determine the optimum configuration. Frequently its use may cause distortion in the image, requiring retuning by a service technician. Moreover, because the Mu metal redirects the magnetic fields, it is possible to actually increase fields, rather than reduce them. And last but not least, CRT-style VDTs can provide a dangerous electric shock if you don't know what not to touch, since the tube stores up thousands of volts, even when it is not plugged into the wall. In short, using Mu metal is an art rather than a science. In response to users' concerns, many display manufacturers have modified their VDTs to produce lower levels of magnetic radiation. Some low radiation models use a compensating coil adjacent to the deflection coils to create an opposite magnetic field. When the two opposing fields meet, most of the radiation is canceled out. Low radiation displays may also incorporate extra shielding around the yoke and flyback transformer.
HEALTH CONCERNS RELATING TO CRT-STYLE VDTs Manufacturers such as IBM cite studies and reports by reputable organizations such as the American Medical Association to back their position that there is no evidence that VDTs are harmful to pregnant women or to anyone else. In May, 1991, IBM wrote: "Based on our examination of available scientific evidence and on the conclusions of national and international health organizations, we believe our VDTs are safe. . . . We concur with the International Radiation Protection Association which, in conjunction with the World Health Organization, stated that available epidemiological data 'do not provide any basis for health risk assessment useful for the development of exposure limits.'" Meanwhile IBM has obtained a patent on a device which reduces VDT radiation and the company is using this technology to reduce the EMF coming from its displays. Other studies concerning the effects of EMF on embryos show reason for concern. According to Dr. Ezra Berman of the Environmental Protection Agency, "the Henhouse Study [of chicken embryos exposed to low frequency magnetic fields] performed in four countries has contributed significantly to the growing database implicating an association of [EMF with an] increase of abnormalities in chick embryos." Expert Louis Slesin, publisher of VDT News, says "the new results should help convince skeptics that magnetic fields can be biologically active at very low levels."
However, pregnant women and their unborn fetuses are not the only ones at risk. CRT-style VDTs can emit levels of ELF magnetic radiation which is far higher than 2 to 3 mG (the level associated with higher risks of brain tumors, leukemia and other cancers). A link between VDT use and cancer has not been established, but this does not mean there is no danger. Consider the fact that the vast majority of VDT operators in the U.S. are women and that the incidence of female breast cancer has been rising steadily along with VDT use. Breast cancer now accounts for 29% of all cancers among women, and an astounding 1 out of 9 women will contract the disease. Because of the relatively short period of time computers have been used, more studies are needed before there is conclusive evidence regarding adverse long-term effects. However, with the extremely strong evidence that ELF magnetic radiation increases the incidence of leukemia and brain cancer, some experts fear that long-term VDT use will also be shown to increase the likelihood of contracting cancer, and/or inhibit the ability of the computer operator to fight off cancer that might otherwise be held in check or destroyed by the body's immune system. Remember that power lines have been around for one hundred years and the cancer link is just now being established. It took over 40 years of research to conclusively establish the dangers of smoking. VDTs have only been widely used for the past twenty years. Other less severe problems sometimes associated with VDTs are headaches, fatigue, nausea, dizziness, irritability, skin redness or rashes, and eye strain.
THE SWEDISH STANDARD Sweden has been a leader in developing recommended visual ergonomic and electromagnetic emission standards for computer displays
The Swedish guidelines have received a formal embrace from many major manufacturers of computer displays. Yet even in Sweden there is not a complete consensus on the limits. A major Swedish union (the Swedish Confederation of Professional Employees, or TCO) is seeking more stringent limits and test protocols F as low as 2 mG for ELF magnetic fields at 30 cm (12 inches) from the front of the screen. Their reasoning is that levels above 2 mG have been linked to increased risks of cancer, and that many VDT users' heads, hands and/or breasts are often closer than 50 cm from the screen. Some experts have also questioned the validity of .25 mG for VLF, pointing out that the higher frequency VLF field contains more energy than ELF. These experts say that if induction levels are used to measure the amount of energy in the radiation, then 2.5 mG of ELF is equal to .01 mG of VLF. MPR's response is that "there are no proven biological reasons" for limiting VDT EMFs, and that the guidelines are not based on health risks. Rather, the recommended limits are based on what is technically feasible to measure and on what is achievable "today or within the near future."
This presents a dilemma for VDT users: If a computer display meets the Swedish guidelines, is it safe? No one can say for sure, since there are no conclusive studies which quantify the danger. On the other hand, there is no harm in being cautious. This means when buying a VDT you should know whether it meets just MPR 1 (in which case the ELF fields could still be quite high), or whether it complies with MPR 2, which includes ELF measurements. Purchase your low radiation VDT from a reputable company, or bring along a Gauss meter and buy the display with the lowest emission levels, not just the one which claims it meets the Swedish standard.
The United States does not have any regulations governing ELF and VLF emissions from VDTs. FCC requirements deal only with radio frequency emissions. For health enthusiasts,
NON-CRT DISPLAYS LCDs (liquid crystal displays) are commonly used in portable laptop and notebook computers. Many experts consider LCDs safe, believing that they have lower EMF levels.Since LCDs are backlit or sidelit with fluorescent lights, they emit magnetic fields in the ELF and VLF range. The strength of the ELF and VLF magnetic fields coming from an LCD vary greatly, depending upon the manufacturer. Although LCD magnetic fields are less than those produced by CRT-style VDTs at comparable distances, at 6 inches some laptops emit up to 22 mG of ELF magnetic fields, and 2 mG of VLF fields and that far exceeds the levels set under the Swedish MPR 2 guidelines at 20 inches. This is significant because a laptop may actually be placed on a person's lap.
TELEVISIONS TVs emit the same assortment of radiation as computer displays, since both devices incorporate a cathode ray tube (CRT). Fortunately, a viewer doesn't have to sit right next to a television set to still see the image. Sitting ten feet away from a 19 inch TV distances the viewer from any measurable ELF or VLF fields. Some televisions, though, are particularly strong, so it makes sense to test your TV with a Gauss meter. A Gauss meter is also useful when buying a TV, since sets can vary quite a bit from one another.
Many appliances generate AC electric and AC magnetic fields, even when they are turned off. For example, televisions with remote controls still have current flowing when not in use. This current generates EMF, although it is less than when the TV is in use. Radios, too, may produce EMF even when turned off. If you need to watch TV in a confined space, you should consider purchasing a small LCD TV. They have quite a strong electric field at 1 inch, but at the distance of 1 foot,the magnetic fields are negligible.
ELECTRIC BLANKETS Electric blankets create an AC magnetic field that penetrates about 6 or 7 inches into the body. Thus it is not surprising that an epidemiological study has linked electric blankets with miscarriages and childhood leukemia. This pioneering work was performed by Dr. Nancy Wertheimer and Ed Leeper, who originally discovered that magnetic fields were linked to childhood leukemia.
In response to EMF concerns, the major U.S. electric blanket manufacturers: Fieldcrest, Casco-Belton and Northern Electric (Sunbeam) have come out with "zero magnetic field" |
