Super Metroid

Source: Paul Brodeur, "The Magnetic Field Menace," in "Macworld," July 1990, pp. 136-145. Via Toxbase.

Various graphics appear in this magazine article. If you want a copy of this article, please contact Melinda Lawrence, Greenpeace USA, 4649 Sunnyside Ave. N., Seattle, Washington 98103, (206) 632-4326; or via Environet (or via Greenlink, for Greenpeace staff).

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THE MAGNETIC-FIELD MENACE

Computer monitors may pose a very real threat to users

    As the new decade begins, most Macintosh users and other inhabi-

tants of the vast computer community have become aware that serious questions are being raised about the potentially harmful health ef- fects of electromagnetic emissions from display monitors. However, the issue has been so shrouded by denial on the part of manufacturers and employers, and addressed with such incompetence by state and federal regulatory agencies, that computer users scarcely know what to think about it, who to turn to for reliable information, or how to protect themselves. Meanwhile, industry, government, and the medical and scientific community are mounting belated attempts to study the problem and reach some consensus about how to deal with it.

    Since disease does not develop by consensus but by immutable laws 

of biology, it seems prudent to review what is known about the harmful biological effects of low-level electromagnetic emissions from display monitors, power lines, and other sources -- particularly magnetic- field emissions, which have been linked for more than ten years to the development of cancer -- and to understand how this knowledge has been acquired and disseminated. It also seems sensible to determine the strength of magnetic-field emissions from monitors -- something that has not been done with accuracy to date -- and to relate these emis- sions, insofar as possible, with what is known about their potential for harm.

    For this reason, "Macworld" has undertaken to conduct careful 

measurements of the strength of the magnetic fields given off by monitors that are commonly used with the Macintosh. The idea is to provide accurate readings so that Macintosh users can determine for themselves whether they wish to take protective measures in order to reduce their exposure to magnetic fields (see "At Arm's Length").

FIRST SUSPICIONS

    Radiation from computer terminals first became an issue in 1977, 

when officials of the National Institute for Occupational Safety and Health (NIOSH) measured emissions from several display monitors at the "New York Times," where two young copy editors had developed incipient cataracts after working on the machines for periods of a year or less. The NIOSH officials reported that the electric-field and magnetic- field strengths of the VLF (very-low-frequency) radio-frequency radia- tion being emitted were too weak to be detected by their instruments at a distance of 4 inches. As it turned out, they were trying to measure the fields in terms of milliwatts per square meter, even though VLF and ELF (extremely-low-frequency) fields can't be accurate- ly measured in this manner.

    Early in 1980, NIOSH officials measured VLF magnetic-field 

strengths of almost 9 milligauss (a gauss is a unit of strength of the magnetic field, and a milligauss is 1/1000 gauss) near the flyback transformers of several display monitors at newspapers in San Francis- co and Oakland, California. The NIOSH officials discounted the health hazard of these fields, claiming that "there is no occupational stand- ard for this frequency and these frequencies have not been shown to cause biological injury."

    During the next two years, seven unusual clusters of birth de-

fects and miscarriages involving women who operated video-display terminals (VDTs) were reported in Canada and the United States. Instead of taking their own measurements of the machines in question, however, the health officials who investigated these cases relied on the flawed NIOSH reports and characterized each of the clusters as a chance occurrence. By this time, the regulatory officials and comput- er manufacturers of both nations seemed to be falling over one another in their haste to absolve computers of any blame.

    In March of 1981, the director of Canada's Radiation Protection 

Bureau declared that VDTs "carry no radiation hazard." Similar claims were made before a congressional subcommittee by the U.S. Food and Drug Administration's Bureau of Radiological Health and by the direc- tor of standards for IBM. In October of that year, a senior scientist at the Bell Telephone Laboratories in Murray Hill, New Jersey, de- clared that computer terminals "do not represent a health hazard from any radiation exposure caused by their use." (At the time, there were well over 100,000 computer terminals in operation in the Bell systems.)

60HZ HAZARDS EXPOSED

    Unaccountably, no one in industry or government said a word about 

the pulsed 60Hz electric and magnetic fields that were being emitted by display monitors (see "Cathode-Ray Tubes Explained"), even though there were by then many studies in the medical literature to suggest that the 60Hz alternating-current fields given off by power lines might be hazardous to health. Chief among these studies was one that had been published in March of 1979 in the highly respected "American Journal of Epidemiology" by epidemiologist Nancy Wertheimer and physi- cist Ed Leeper, who live in Boulder, Colorado. Wertheimer and Leeper had conducted an investigation showing that children in the Denver area who lived in homes near electric distribution wires carrying high current had died of cancer at twice the expected rate. (Since magnet- ic fields are produced by electric current, distribution wires carry- ing high current produce relatively strong magnetic fields -- invisi- ble lines of force that readily penetrate almost anything that happens to stand in their way, including the human body.)

    In their article, Wertheimer and Leeper pointed out that magnetic 

fields in homes near high-current wires might reach levels of 2 milli- gauss or more "for hours or days at a time," and that if magnetic- field exposure were responsible for the increased incidence of child- hood cancer they had observed, the duration of exposure might be an important factor. They also suggested that the magnetic fields from power lines might be promoting cancer in children by hindering the ability of the body's immune system to fight the disease.

    Instead of taking Wertheimer and Leeper's disturbing findings as 

a sign that the magnetic-field problem should be thoroughly investi- gated, the electric-utilities industry tried to discredit their work. But in 1986 the association between magnetic fields from high-currency wires and childhood cancer was confirmed by a major study conducted under the auspices of the New York State Department of Health. This investigation reported that "prolonged exposure to low-level magnetic fields may increase the risk of developing cancer in children." Earlier, a similar finding was announced by scientists studying child- hood cancer in Sweden. What should have been of profound concern to the manufacturers and users of display monitors was that the incidence of cancer in all three childhood studies was associated with 60Hz magnetic-field strengths of only 2 to 3 milligauss.

COMPUTER MONITORS IMPLICATED

    The fact that display monitors emit significant radiation in the 

form of pulsed ELF electric and magnetic fields did not come to light until October of 1982. At that time, Dr. Karol Marha, a biophysicist at the Canadian Centre for Occupational Health and Safety (CCOHS) in Hamilton, Ontario, revealed that Canadian researchers had measured 60Hz magnetic fields greater than 2 milligauss at distances of 12 inches from two display monitors, and fields of approximately 1 milli- gauss at a distance of 20 inches from several screens. In 1983, CCOHS issued press releases carrying Marha's warning that there was scien- tific evidence to suggest that pulsed electric and magnetic fields could be more harmful than nonpulsed fields, as well as his recommen- dation that workplaces be redesigned so that VDT operators do not sit close to their display monitors or to neighboring monitors.

    Marha's recommendations were ignored by government health offi-

cials in Canada and the United States, who failed to appreciate the possible connection between the potential health hazard of alternat- ing-current 60Hz power-line magnetic fields and that of the pulsed 60Hz magnetic fields given off by display monitors. Moreover, the CCOHS press releases were not picked up by any major newspaper in the United States or Canada. A year later, the medical director of the "New York Times" told a congressional subcommittee that he was aware of "no medical evidence of serious VDT-related health effects." By then, of course, newspapers everywhere had become highly dependent upon computer technology.

SUPPORTING EVIDENCE

    In July of 1982, shortly before Marha's announcement that 

display monitors were emitting potentially hazardous electric and magnetic fields, Dr. Samuel Milham, Jr., a physician and epidemi- ologist for the Washington State Department of Social and Health Services, published a letter in the "New England Journal of Medicine" that furnished a new insight into the problem. Milham had examined that data for 438,000 deaths occurring between 1950 and 1979 among workers in Washington State and had found that leukemia deaths were elevated in 10 out of 11 occupations involving exposure to electromag- netic fields. His pioneering study provided the starting point for some 20 subsequent investigations here and abroad, which showed that persons whose occupations require them to work in electromagnetic fields -- among them electricians, electrical engineers, and tele- phone- and power-line workers -- die of leukemia and brain cancer at a much higher rate than other workers.

    For example, a 1984 study demonstrated that a significantly 

higher than expected number of Maryland men who had died from brain cancer had been employed in electrical occupations, and a 1988 study of men who had died of brain cancer in East Texas revealed that the risk for electric-utility workers was 13 times greater than that for workers who were not exposed to electromagnetic fields.

    Additional cause for concern came in November of 1989 with the 

announcement that a study conducted by epidemiologists at the Johns Hopkins University School of Hygiene and Public Health, in Baltimore, had found an elevated risk of all cancers among cable splicers working for the New York Telephone Company. Indeed, the incidence of leukemia among these men, who often work close to power lines, we 7 times that of other workers in the company. Moreover, measurements of their on- the-job exposure showed that the mean level of the 60Hz alternating- current magnetic-field strengths to which they had been subjected was only 4.3 milligauss. Considering the fact that a pulsed ELF magnetic filed level of between 4 and 5 milligauss has been measured at a dis- tance of 12 inches from the Apple 13-inch color monitor and from E- Machine's Color-Page 15, this is a discomfiting finding, to say the least.

LABORATORY STUDIES CONCUR

    While epidemiologists were investigating the incidence of cancer 

among human beings exposed to low-level electromagnetic fields, other scientists were studying the effect of weak ELF fields on test ani- mals. Chief among them was Dr. W. Ross Adey, a clinical neurologist and neuroscientist, who was formerly the director of the Brain Re- search Institute at the University of California at Los Angeles and is now associate chief of staff for research at the Jerry L. Pettis Memorial Veterans' Hospital, in Loma Linda, California. During the 1970s, Adey and his colleagues discovered that weak ELF electromagnet- ic fields altered brain chemistry in living cats. During the 1980s they found that low-level electromagnetic fields can interfere with the ability of T-lymphocyte cells -- the soldiers of the immune system -- to kill cancer cells, which suggests that these fields may be acting as cancer promoters by suppressing the immune system.

    In 1988, Adey and his associates demonstrated that weak 60Hz 

electric fields similar in strength to those that can be found i the tissue of a human being standing beneath a typical over-head high- voltage power line (or, for that matter, in the tissue of someone standing very close to a display monitor) could increase the activity of an enzyme called ornithine decarboxylase, which is associated with cancer promotion.

    Back in 1980 and 1981, even as government health officials in the 

United States and Canada were denying any possible connection between electromagnetic emissions from display monitors and adverse pregnancy outcomes among women who worked with those machines, Spanish research- ers were conducting experiments showing that when chicken eggs were exposed to weak pulsed ELF magnetic fields, nearly 80 percent of them developed abnormally, with malformations of the cephalic nervous system being particularly prevalent. The adverse effect of pulsed magnetic fields upon the development of chick embryos was confirmed in 1984 by scientists at the Swedish National Board of Occupational Safety and Health.

    Later that year, however, Professor Arthur W. Guy, director of 

the Bioelectromagnetic Research Laboratory at the University of Wash- ington, in Seattle, who had been hired by IBM to review the literature on the biological effects of VDT emissions, pointed out that the weak magnetic-field pulses used by the Spanish researchers did not match the sawtooth shape of the pulses emitted by computer display monitors, and concluded that there was no valid evidence that monitor emissions posed any health hazard.

FURTHER INDICATIONS

    Early in 1986, Guy's criticism was addressed in a Swedish study 

conducted by Dr. Bernhard Tribukait, a professor of radiobiology in the Department of Radiobiology of the world-renowned Karolinska Insti- tute, in Stockholm. Together with a colleague, Tribukait discovered that the fetuses of mice exposed to weak pulsed fields with the same sawtooth shape as those given off by display monitors experienced more congenital malformations that did the fetuses of unexposed test ani- mals. (This finding was reported by Tom Brokaw on "NBC Nightly News," but went unmentioned by the "New York Times" and virtually every major daily newspaper in the United States.)

    In the spring of 1987, Dr. Hakon Frolen, of the Swedish Universi-

ty of Agricultural Sciences, in Uppsala, Sweden, reported that he and a colleague had found a significant increase in fetal deaths and fetal losses by resorption (a phenomenon similar to miscarriage in humans) among pregnant mice exposed to weak pulsed magnetic fields, compared with those occurring in nonexposed test animals. In June, other Swedish scientists reported that radiation similar to that emitted by display monitors could cause genetic effects in exposed tissue sam- ples. An important aspect of all three Swedish studies was that the radiation exposure in each of them had been designed to mimic as closely as possible the sawtooth magnetic-field pulses emitted by VDTs.

    Further evidence that weak pulsed magnetic fields might be haz-

ardous to health came in the spring of 1988, when the combined results of a six-laboratory experiment conducted in the United States, Canada, Spain, and Sweden confirmed the earlier finding that such fields could indeed adversely affect the development of chick embryos. Later that year, Frolen found that the fetuses of pregnant mice were most sensi- tive to pulsed magnetic fields in the early stages of pregnancy, which was consistent with a similar observation by Canadian and Spanish researchers.

    At the second international VDT conference, which was held in 

Montreal in September of 1989, Frolen described a series of experi- ments in which he delayed exposing pregnant mice to pulsed magnetic fields for up to nine days after conception. The results were strik- ing. All of the mice that were exposed immediately after conception, or on the first, second, or fifth day after conception, had statisti- cally increased rates of resorption.

    Louis Slesin, the editor and publisher of VDT NEWS -- a 

newsletter that reports six times a year on the biological effects of display monitors (see "Conspicuous Consumer," in this issue, for con- tact information) -- has emphasized the importance of Frolen's find- ings, pointing out that the lack of any effect after the ninth day following conception "clearly indicates that the pulsed magnetic fields -- not some as-yet-unrecognized factor -- are damaging the embryos."

INDUSTRY RESPONSES

    Meanwhile, the Coalition for Workplace Technology -- a powerful 

lobbying group set up by the Computer and Business Equipment Manufac- turers Association (CBEMA) and strongly supported by IBM -- had been lobbying since 1984 in various state legislatures against laws de- signed to protect the health of VDT workers. Computer manufacturers continued to scoff at the idea that their devices might emit hazardous radiation. One industry spokesperson, Charlotte Le Gates, the direc- tor of communication for CBEMA, declared that for pregnant operators to ask to be transferred away from VDTs "is like asking to be trans- ferred away from a light bulb."

    By using this simile repeatedly, computer manufacturers and their 

paid consultants in CBEMA and the Center for Office Technology have been unquestionably successful in allaying growing concern among computer users that the emissions from display monitors might be hazardous. The comparison is specious and unscientific, however. A light bulb emits no magnetic field whatsoever -- a fact that can easily be ascertained by holding a gauss meter (a device that measures the strength of a magnetic field) to an incandescent light bulb. As the accompanying measurements taken by "Macworld" clearly show (see "Macworld Tests"), however, many display monitors DO emit magnetic fields that are as strong or even stronger than the magnetic-field levels that have been associated with the development of cancer in children and workers.

RISK ACKNOWLEDGED

    The accumulation of evidence suggesting that the electromagnetic 

fields given off by display monitors may be hazardous, together with the fact that there are now some 40 million computer terminals in the workplace, raises the question of why so few epidemiological studies have been conducted in the United States to determine whether monitor emissions are affecting the health of American users. Astonishingly, only one major epidemiological study has so far been conducted in this country. It was performed by researchers at the Northern California Kaiser Permanente Medical Care Program, in Oakland, who conducted a case-control study of 1583 pregnant women who had attended Kaiser Permanente obstetrics and gynecology clinics during 1981 and 1982.

    In an article entitled "The Risk of Miscarriage and Birth Defects 

among Women Who Use Visual Display Terminals During Pregnancy" ("American Journal of Industrial Medicine," June 1988), Kaiser re- searchers wrote that they had found that women who worked with VDTs for more than 20 hours a week experienced a risk of both early and late miscarriage that was 80 percent higher than the risk for women who performed similar work without using VDTs. In their conclusion, the researchers stated, "Our case-control study provides the first epidemiological evidence based on substantial numbers of pregnant VDT operators to suggest that high usage of VDTs may increase the risk of miscarriage."

APPLE RESPONDS

    As might be expected, the results of the Kaiser Permanente study, 

together with the Swedish experiments demonstrating that the emissions from display monitors can adversely affect the fetuses of test ani- mals, have prompted many computer users to write to computer manufac- turers to ask whether their monitors are safe to use. One such letter was sent on November 5, 1989, to John Sculley, chief executive officer of Apple Computer, by Professor Harris Barron, who taught electronic media in art-making at the Massachusetts College of Art in Boston for 25 years. In his letter, Barron told Sculley that he was writing on a Macintosh SE; that his young daughter-in-law, "an avid law school scholar, sits long hours at the terminal of her own SE"; and that "she and her computer-user husband intend to raise a family in the near future." (As the reader will note in "Macworld Tests," MACWORLD has measured an ELF magnetic field of slightly more that 2 milligauss at a distance of 12 inches from the screen of the SE display monitor.) Barron then asked whether his daughter-in-law was at risk from the electromagnetic fields emitted by her monitor and told Sculley that "the results of any studies that Apple has made in this regard would be helpful."

    On December 6, 1989, Barron received an unsigned letter from 

the Apple Customer Relations Department, thanking him for his letter and informing him that some materials were enclosed for his perusal. The enclosed material consisted of an article from the February 1984 issue of "Health Physics," which said that X-ray emis- sions from VDTs posed no health problem; some 1984 recommendations by the European Computer Manufacturers Association on how to avoid ergo- nomic problems from VDT use; a 1983 policy statement issued by the American Academy of Ophthalmology, which said that VDTs presented no hazard to vision; and some 1985 Apple safety data sheets about the testing of toner materials.

    On December 11, 1989, Barron wrote to Sculley to express disap-

pointment with Apple's response to his initial query. "With your pro forma mailing, I am now armed with 1984 materials, data so antiquated that I would be embarrassed to use it, as would Apple in any of its public relations," Barron said. "Reprints of ergonomic factors, ocular data, toner safety data, and the 'put-to-bed' X-ray issue totally ignored my one basic question on permanent harm from ELF magnetic-field VDT emissions." In conclusion, Barron told Sculley that he intended to prepare a statement about his correspondence with Apple for circulation to his contacts in higher education, including the National Education Association.

FURTHER EQUIVOCATIONS

    On January 9, 1990, Barron received a reply to his second letter 

from David C. McGraw, Apple's newly appointed manager for corporate environmental health and safety. McGraw apologized for the delay and confusion in getting back to Barron, and assured him that "the pro forma response to your initial letter dated 11/5/89 is not the way Apple wishes to respond to this important issue." He went on to tell Barron that "Apple believes that no increased risk of adverse pregnan- cy outcome due to VDT work has been demonstrated," and to point out that Apple's position in this regard "is supported by the American Medical Association, the American College of Obstetricians and Gyne- cologists, the National Institute for Occupational Safety and Health (NIOSH), and the World Health Organization (WHO)."

    McGraw said that the Kaiser Permanente study "drew public atten-

tion because of what appeared to be an increase in miscarriages among women who use VDTs more than 20 hours per week," but that the re- searchers who conducted it "were unable to determine the specific cause of the increased rate of miscarriages." He then noted that "similar studies in Canada and Scandinavia have found no relationship between VDT work and adverse pregnancy outcome." McGraw enclosed the results of a recent animal study that had been conducted for IBM and Ontario Hydro by researchers at the University of Toronto, who, unlike Drs. Frolen and Tribukait, had found that pulsed magnetic fields did not adversely affect the fetuses of test mice. He also recommended that Barron read a compendium entitled LATEST STUDIES ON VDTs, pub- lished in August 1989 by the Center for Office Technology. (This is the new name of the Coalition for Workplace Technology of the Computer and Business Equipment Manufacturers Association, which had previously assured computer users that the emissions from a display terminal were no different than those from a light bulb.)

    In January of this year, McGraw sent Barron the names and resumes 

of three people whom he described as "experts in the field of biologi- cal effects of electromagnetic radiation." One was Edwin L. Carsten- sen, a professor of electrical engineering at the University of Roch- ester, who had been a paid consultant of the electric-utility industry for nearly 15 years and has testified for power companies in court cases on several occasions. Another was Kenneth R. Foster, a profes- sor in the Department of Bioengineering at the University of Pennsyl- vania, who has not only discounted the possibility that low-level electromagnetic radiation can have adverse biological effects but has even suggested that restrictions be placed on further investigation of the problem. The third was Eleanor R. Adair, a physiologist at the John Pierce Foundation, in New Haven, Connecticut, who, in spite of dozens of scientific studies published in leading scientific journals around the world demonstrating that weak pulsed electromagnetic fields given off by display monitors and low-level fields emitted by radar and other sources can cause adverse biological effects at field strengths far below those necessary to produce heat, has recently been quoted as saying that she has "never seen one bit of scientific evi- dence -- and let me emphasize the word SCIENTIFIC -- that ELF or microwave radiation has any nonthermal biological effects."

ANSWERING CRITICS

    Macintosh and other computer users must now decide for themselves 

whether monitor manufacturers are dealing forthrightly with the issue of display monitor emissions. It is clear that computer users are being asked by manufacturers to extend the presumption of benignity to the pulsed electric and magnetic fields given off by display monitors, even as scientists continue to investigate the apparent health hazard posed by these emissions. One of the chief rationales behind this strategy is the belief that there is no "conclusive" proof that VDT emissions have any harmful effects on computer users. Another is that no biological mechanism has yet been postulated to show exactly how pulsed magnetic fields might cause miscarriages and cancer. In other words, if scientists can't explain how something is happening, it can't be happening. Someone should remind the monitor manufacturers that scientists don't know exactly how inhaled asbestos fibers act to cause cancer; yet everyone knows that asbestos causes cancer, and only fools would willingly expose themselves to asbestos.

    As it happens, a model of how a 60Hz alternating-current magnetic 

field may cause or promote cancer has been provided by Dr. Harris Busch, an oncologist, who was chairman of the Department of Pharmacol- ogy of the Baylor University College of Medicine in Houston for 25 years and was also formerly an editor of the distinguished "American Journal of Cancer Research." After explaining that a 6 60Hz alternat- ing-current magnetic field vibrates to and fro 60 times a second, Busch points out that there will be a similar to-and-fro movement on the part of anything magnetic in such a field. According to Busch, this means that "any kind of molecule that is in a person's brain, or in a person's body, is being twisted 60 times a second up and back."

    Recently, Dr. W. Ross Adey has made the point that in the case of 

weak electromagnetic fields given off by display monitors, the tissue responses can take account of the regularity of the repeating pulses and assume the rhythm of those pulses in a phenomenon called ENTRAIN- MENT, which, in turn, can alter the normal activation of enzymes and cellular immune responses in ways consistent with the promotion of cancer.

    One does not need to be a medical doctor to appreciate that such 

electromagnetic phenomena, which have no counterpart in man's evolu- tionary history, may well prove hazardous to health.

---

Author: PAUL BRODEUR, a staff writer at the "New Yorker" since 1958, specializes in medical and science writing. The winner of many na- tional awards for his reporting on the dangers of asbestos, the haz- ards of enzymes in household detergents, the destruction of the ozone layer, and the effects of electromagnetic emissions, Brodeur's most recent book is "Currents of Death" (Simon and Schuster, 1989).

---

[GRAPHIC ARTICLE INSERTS:]

CATHODE-RAY TUBES EXPLAINED

    Computer display monitors operate on much the same principle as 

television sets. An evacuated glass tube containing an electron gun, called the cathode-ray tube (CRT) (A), produces a narrow electron beam (B); a step-up transformer known as the flyback transformer (C) then accelerates and directs the beam toward the front of the tube. When the beam strikes the inner surface of the CRT screen, it interacts with a phosphor coating (D) on the face of the tube to generate a spot of visible light.

    To produce a screen image, the electron beam sweeps from left to 

right and from top to bottom in a series of raster line (E). The movement of the electron beam is controlled by deflection coils (F) wound like a yoke around the neck of the CRT; electric current flowing through the coils produces magnetic fields that control the electron beam. Increasing current in the horizontal-deflection coil forces the beam from left to right; a drop in current causes the beam to return to the left. Meanwhile, an increase in the vertical-deflection coil's current aims the beam down a line. This pulsing actions results in a sawtooth waveform (G).

    The horizontal-scan frequency for a typical computer monitor is 

generally between 10kHz and 30kHz, which falls in the very-low-fre- quency (VLF) range. Because most monitors operate at 60 to 75 frames per second, their vertical-scan frequency is between 60Hz and 75Hz, within the extremely-low-frequency (ELF) range. Both electric and magnetic fields are generated in the ELF and VLF ranges.

    In addition, 60Hz alternating-current (AC) fields originate in 

the monitor's power transformer. (60Hz AC current flows back and forth 60 times a second.) Since the AC fields decay rapidly over distance, they can usually be measured only in the immediate vicinity of the power transformer. -- P.B.

ELECTROMAGNETIC SPECTRUM

    While all electromagnetic radiation, from the longest radio wave 

to the shortest gamma ray, travels at 186,000 miles per second -- the speed of light -- visible light makes up only a small portion of the spectrum. AS the wavelength (shown in meters) increases, the frequen- cy (shown in hertz, or cycles per second) decreases. Display monitors give off several types of electromagnetic emissions; most of the emissions consist of pulsed radio-frequency (VLF) electric and magnet- ic fields of between 15 and 20kHz and pulsed ELF electric and magnetic fields of 60Hz. The ELF magnetic fields is the dominant waveform given off by VDTs. -- P.B.

MACWORLD TESTS

    To determine the strength of the ELF magnetic fields emitted 

by monitors regularly used with Macintosh computers, MACWORLD tested ten monitors in our labs. Using the Holaday HI-3600-02 ELF/Power Frequency EMF Survey Meter, we measured emissions at 4, 12, 28 (arm's length), and 36 inches from the center of the front, back, left, right, top, and bottom of the monitors. (For logistic reasons, we could not complete all the measurements from the bottom.) While it is important to note that magnetic-field strengths may vary somewhat from monitor to monitor, even within a single product line, the overall test results do confirm that ELF magnetic-field emissions from monitors used with the Macin- tosh are worrisome.

    The strongest emissions are at the sides and tops of the 

monitors -- over 70 milligauss (mG) 4 inches from the right side of the AppleColor High-Resolution RGB Monitor, for instance. At the same distance from the front, emissions are over 22mG for the Apple monitor and the E-Machines ColorPage 15. As detailed in the main article, levels much lower than these have been corre- lated with cell mutation and cancer in humans. At 28 inches (arm's length), however, the emissions from the front fall to below 1mG.

AT ARM'S LENGTH

    While ELF magnetic-field emissions of roughly 5 to 23 milli-

gauss (mG) were found at 4 inches from the front of monitors commonly used with the Macintosh, "Macworld" found that at 28 inches from the screen, all the monitors tested at less than 1mG. (The ambient ELF magnetic-field emissions measured in the MACWORLD offices ranged from 0.1 to 0.5 mG.) Macintosh users wishing to reduce exposure to pulsed electromagnetic fields should position their display monitors at arm's length (with fingers extended)(A).

    Because magnetic fields emitted from the sides and backs of most 

monitors are considerably stronger than those given off from the front, users should consider maintaining a distance of at least 4 feet from the sides or back of any other monitor in the workplace (B). Keep in mind that magnetic-field emissions are not stopped by cubicle partitions, walls, lead aprons, or even the human body.

    Curiously, there are no standards for ELF magnetic-field emis-

sions, although several countries, Sweden and Canada among them, have developed standards for VLF magnetic-field emissions. A number of vendors -- IBM, DEC, and Phillips, for instance -- market monitors for PCs that meet those standards. For the past two years, Sigma Designs has supplied the European market with monitors for the Mac that meet the VLF standards, and American users can now special order these monochrome and gray-scale 15-, 19-, and 21-inch monitors. Also, any monitor based on a technology other than a cathode-ray tube will have the advantage of not emitting the types of pulsed radiation associated with vertical-and horizontal-deflection coils. For a discussion of various products that claim to mitigate monitor emissions, see "Con- spicuous Consumer" in this issue.

    The controversy surrounding low-frequency electromagnetic emis-

sions will continue until further research is completed. In the meantime, prudent avoidance -- sitting at arm's length from the front and 4 feet from the sides or back of a monitor -- is a sensible solu- tion. "Macworld" is committed to documenting any new developments as they relate to this issue. Stay tuned. --Suzanne Stefanac.

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