VDT Work and Your Health:
Radiation

Table of Contents
Do computers emit radiation?
How are ELF/VLF fields generated? Electric fields Magnetic fields
Field measurements Are there standards for ELF/VLF exposure?
Are these ELF/VLF fields harmful? Teratogenic effects Cellular effects
Epidemiological studies What conclusions can be drawn?
What can I do? Where can I read more? References

Do computers emit radiation?

Radiation occurs in many differ ent forms characterized by different frequencies and field strengths. The primary concern in computer use is radiation emitted by the visual display unit, or VDT. Most VDTs do emit radiation, particularly low frequency fields.

High-energy ionizing radiation (X-ray) emission is not a VDT health risk. Although radiation within the X-ray band is produced in VDTs, it is absorbed by the thick glass of the screen before it can be emitted.

Likewise, microwave and ultraviolet radiation are well within established limits of safety. Unlike x-rays, these frequencies of nonionizing radiation do not break chemical bonds in molecules. They could cause damage by raising cell temperature, as a microwave oven heats food or overexposure to a sunlamp causes sunburn, but not in the small amounts generated by a VDT.

In short, the amount of X-ray, microwave, and ultraviolet radiation generated by a VDT are all far below the established safety thresholds.

Recently, however, attention has focused on very low frequency (VLF) and extremely low frequency (ELF) nonionizing radiation – frequencies which were previously believed to have no biological effect. Almost all video display terminals emit both VLF and ELF fields.

This radiation has become cause for concern because some studies indicate that even weak VLF or ELF fields can cause miscarriage, birth defects, or cancer. However, these studies are extremely controversial. The purpose of this paper is to describe the nature of the ELF/VLF controversy and to suggest some ways to manage the alleged risk while waiting for new findings.

How are ELF/VLF fields generated?

In order to understand how radiation is generated by VDTs, some background information is helpful.

In standard cathode ray tube VDTs, an electron beam strikes phosphors on the inner surface of the screen, creating a spot of visible light. The electron beam scans quickly across each row of phosphors, moves to the beginning of the next row, and when the entire screen has been scanned, returns to the top corner and starts again, as illustrated in Figure 1. The horizontal and vertical movement of the electron beam is controlled by pulses of electric current passing through deflection coils. It is this current that generates VLF and ELF fields.

Horizontal movement of the electron beam is controlled by current passing through a deflection coil. High current in the coil causes the beam to be deflected across the screen. When the beam reaches the far edge, the current in the horizontal deflection coil falls rapidly, causing the beam to move back to the other side of the screen, and so on for each row of phosphors on the screen. Thus, current in the horizontal deflection coil rises and falls rapidly each time the beam crosses the screen.

At the same time, another deflection coil controls vertical movement of the beam. Increasing current in this coil causes the beam to move downward on the screen. When the beam reaches the bottom of the screen, the current drops, and the beam returns to the top of the screen. Thus, current in the vertical deflection coil rises and falls less rapidly than that in the horizontal coil – once for each complete scan of the screen.

In order to ensure that the image on the screen does not flicker, the scanning process must occur very rapidly. In a typical 12\" monochrome monitor, the beam moves across the screen almost 16,000 times each second, creating a horizontal scan rate of 15.72 kHz (Marha, et. al., 1986). The beam covers the entire screen from top to bottom about 60 times each second, for a vertical scan rate of 60 Hz. Higher resolution monitors require even faster scanning rates to ensure a constant image.

Electric fields

Electric fields result from the amount of charge and are generally expressed in volts per meter (V/m). Fields are distinguished according to the frequency of the pulsing current: very low frequency (VLF) fields are generally considered to be between 2 kHz and 400 kHz, and extremely low frequency (ELF) fields between 5 Hz and 2 kHz.

In a VDT, very low frequency fields are produced by current in the horizontal scan mechanism. Extremely low frequency fields are created by current in the vertical scanning mechanism. The specific ELF and VLF fields emitted by any given monitor are determined by the scan rates for that monitor, generally between 15 and 70 kHz.

In addition, VLF fields are produced by the step-up transformer (also known as the flyback transformer) used to accelerate and focus the electron beam. This transformer increases the voltage to around 10 to 25 kilovolts; the voltage requirement increases for color or oversize monitors.

Sixty-hertz fields are emitted by the power transformer, but these fields decay rapidly over distance and are measurable only in the immediate vicinity of the transformer (generally at the side or rear of the VDT).

The ELF and VLF fields generated by the step-up transformer and the deflection coils are pulsed fields. In particular, the rapid rise and very rapid fall of current in the deflection coils gives them a distinctive sawtooth shape.

Because of the location of the deflection coils, field intensity varies with position and distance. The highest levels are generally at the side and rear surface of the VDT, decreasing with distance from the unit.

Magnetic fields

Magnetic fields result from the motion of a charge – current passing through a wire creates a magnetic field around the wire. The proper unit of magnetic field intensity is amperes per meter (A/m), but magnetic fields are often described in terms of flux density (the number of field lines that cross a unit of surface area), expressed in gauss (G) or teslas (T). One tesla equals 10,000 gauss, and one gauss equals 1/80 A/m in air or biological tissue. Gauss and teslas are relatively large units of measure; milliGauss (mG) or nanoTesla (nT) are more commonly used.

In a VDT, magnetic fields are produced by current flowing in the horizontal and vertical deflection coils. The frequency of the generating current is often used to describe a magnetic field; thus fields generated by the horizontal scan mechanism are frequently referred to in the literature as VLF magnetic fields, while those generated by the vertical scan mechanism are referred to as ELF magnetic fields. Like the electric fields, these are pulsed fields due to the rapid rise and fall of the deflection currents.

Magnetic fields decrease rapidly with distance, but they are very difficult to shield. They are not blocked by walls or partitions, so in some cases fields from other people's VDT may reach your work area.

Actual field measurements

There are relatively few printed reports of electric field measurements around a VDT. Marha (1983) found intensities of up to 300 V/m at 20 cm from the side of a unit, dropping off to 150 V/m at 30 cm and 50 V/m at 40 cm. In front of the screen, levels were generally low, under 10 V/m at 30 cm from the unit.

Most recent measures have focussed on magnetic rather than electric fields. According to Charron (1988), magnetic fields tend to be evenly distributed around the VDT with field strengths ranging from 0.1 to 1 A/m (1.25 to 12.5 milliGauss) at a distance of 30 cm. However, other recent measures have distinguished clear variations in field intensity at different points around VDTs and between different models of VDT.

For example, Infoworld (Copeland, 1990) reported VLF magnetic field measurements at 80 different points for 12 different monitors. At a distance of 50 cm (about 20 inches), four monitors in that group showed very low emissions (less than .12 milliGauss for almost all the measurement points), one showed high emissions (more than .76 milliGauss at all the points), and several showed varying emissions, with \"hot spots\" at the top, bottom, or side of the monitor.

A later Infoworld report (Carlson, 1991) measured VLF magnetic fields around a different group of six monitors. This report used a different (updated) instrument and measurement procedures – most notably, the newer instrument measured average emissions in each location while the older one measured peaks. These measurements were generally lower (the highest recorded field at a distance of 50 cm was 22.4 nanoTeslas, equivalent to .224 milliGauss). Variations between monitors and between different points on the same monitor were still observed. Monitors with relatively low emissions showed ranges of 2.8 to 7.6 nanoTeslas (.028 to .076 milliGauss) while high-emission monitors showed ranges of 6.0 to 22.4 nanoTeslas (.06 to .224 milliGauss).

ELF magnetic fields also vary among monitors and at different points near the same monitor. Macworld has published ELF magnetic field measurements for more than 30 monitors (Brodeur, 1990 and O'Connor, 1991). The measurements show wide variety among models at distances of 4 or 12 inches from the unit, but all measures dropped dramatically at distances of 28 and 36 inches.

Are there any standards for ELF/VLF exposure?

There is no U.S. standard addressing exposure to ELF/VLF fields from a VDT.

The American Conference of Governmental Industrial Hygienists (ACGIH) has issued recommendations for industrial workers based on the frequency of the field. For example, they indicate that routine occupational exposure to 60Hz magnetic fields should not exceed 10 gauss (10,000 mG) and exposure to electric fields of 4kHz to 30 kHz should not exceed 625 V/m (ACGIH, 1991). These recommendations apply to industrial hygiene and were not specifically developed with VDT use in mind.

However, some areas around the country and some countries abroad have introduced legislation covering specific aspects of VDT use.

The San Francisco Board of Supervisors approved legislation in December, 1990 requiring employers with 15 or more workers to comply with certain safety measures related to VDT use. Employers must ensure that workers who use a VDT for four hours or more per shift have adjustable workstations and chairs, adjustable display supports, optional foot rests and wrist rests, detachable keyboards, appropriate lighting, reduced glare, and 15-minute breaks away from the VDT for every two hours of keyboard work (Updegrove, 1991; Steere, 1991; Damore, 1991).

The state of Maine adopted a law in July, 1989 requiring employers with 25 or more VDTs at one location to provide both oral and written education and safety training. A subsequent law required employers with fewer than five VDTs to provide written education and safety training. The state Bureau of Labor Standards recommends literature to be used in the training programs. Beyond that, some Maine employers have further guidelines for VDT use. For example, as part of a collective bargaining agreement the University of Maine System allows pregnant VDT operators to request reassignment to other work not involving regular VDT use. An extended leave of absence may be requested if reassignment is not possible. All workers are granted periods of non-VDT time in their daily work schedule in an effort to reduce potential eyestrain, muscle aches, or other problems (Sauda, 1991a and 1991b).

In Europe, the issue of VLF and ELF exposure is directly addressed. The Swedish National Board for Metrology and Testing (the Mat Oct Provadet, known as MPR) has established guidelines for VLF and ELF electric and magnetic fields at a distance of one-half meter from the unit:

Table 1: Swedish guidelines for VLF and ELF fields
?(Source: Coughlin, 1991).
VLF range ELF range
(2 KHz to 400 KHz) (5 Hz to 2 Khz)
Magnetic fields .25 mG 2.5 mG

(25 nT) (250 nT)
Electric fields 2.5 V/m 25 V/m

These guidelines are actually voluntary in Sweden, but they have been adopted as requirements in other European countries (Chandler, 1991a).

Now look back at the measurements cited on page 4 in light of these recommendations. Marha's 1983 measures of VLF electric fields do not extend to a distance of 50 cm, but the field strength at 40 cm is still quite high relative to the guidelines. Newer models, however, may be shielded to reduce VLF electric fields (Chandler, 1991b).

In the first set of monitors tested by Infoworld (Copeland, 1990), VLF magnetic fields exceeding .25 mG were present in 9 out of 12 cases, including two monitors marketed as "low-emission". In the later set of tests involving different monitors and different measurement techniques (Carlson, 1991), none of the monitors exceeded the Swedish guidelines.

In a PC-Week study (Coughlin, 1991), 20 monitors marketed as low-emission are listed as meeting the Swedish VLF guidelines, although no specific measures are given. In this same set of monitors, 13 of the 20 are listed as meeting the ELF standards. The MacWeek studies cited earlier (Brodeur, 1990 and O'Connor, 1991) are harder to interpret since their measures were not taken at the 50 cm mark used in the Swedish standard. However, at 28 inches (several inches further from the unit), two units had fields greater than the Swedish limit, and several others were close (within .3 mG) to the limit. In each case, the higher intensity fields were at the side of the unit.

Are these ELF/VLF fields harmful?

This question is the source of a great deal of debate. Some studies indicate that even weak VLF or ELF fields can cause miscarriage, birth defects, or cancer. However, these studies – and their implications – are very controversial.

Three types of studies are commonly cited as cause for concern with regard to low frequency non-ionizing radiation:

In order to evaluate the implications of these studies, let's consider some of them more closely.

Teratogenic effects

Delgado et al. (1982) found that fertilized chick eggs exposed for 48 hours to 100-Hz ELF fields of 12 milliGauss showed delayed or arrested development. Nearly 80% of the eggs showed abnormal development, including lack of neural tube, brain vesicles, auditory pit, foregut, or heart. In later experiments, Ubeda et al. (1983) found that the shape of the pulse and the duration of its rise time were important factors in producing the effect.

A set of international follow-up studies nicknamed the Henhouse Project attempted to replicate Delgado's work but found mixed results. Five out of six labs found an increased number of abnormalities, but only two of the six findings were statistically significant (Brodeur, 1989). Additional follow-up studies are in progress.

Brodeur (1989) also cites Scandinavian mouse studies which found that mice exposed to weak pulsed magnetic fields (sawtoothed pulses with intensities of 10-150 milliGauss, similar to those produced by VDTs) had more congenital malformation in fetuses, as well as significant increases in fetal death and loss by resorption among pregnant mice exposed to weak pulsed magnetic fields. According to Brodeur, these studies indicate that the period of greatest sensitivity occurs in early stages of development.

As in all animal research, questions remain about the generalizability of these results to other species.

Cellular effects

Nair et al (1989) provide an exceptionally clear and detailed overview of cellular studies (and indeed of the entire issue of electromagnetic risks) in a background paper prepared by the Office of Technology Assessment. According to their review ELF fields interact with cells at the cell membrane, affecting the permeability of the membrane to ions such as potassium, sodium, chlorine, hydrogen, and calcium.

In particular, ELF fields decrease the outward flow of calcium from the cells. Although it is difficult to determine what effects seen at the cellular level may imply for the organism as a whole, it is important to note that calcium flow across the cell membrane affects things like muscle contraction, egg fertilization, and cell division.

Another area of research at the cellular level involves changes in DNA synthesis and RNA transcription. ELF fields do not appear to disrupt DNA structure or cause mutations like ionizing radiation and chemicals can. However, ELF fields do appear to alter the synthesis rate of DNA and the transcription pattern of RNA, thereby changing the protein patterns and physiological functioning of the cell. Goodman and Henderson (1988), for example, found that 60 and 72 Hz pulsed signals caused detectable changes in protein patterns of cells, and increased total protein production. Again, it is difficult to infer the effect on the organism from these effects at the cellular level, but it is important to note that ELF fields similar to those produced by VDTs (and previously believed to have no biological effect) do indeed produce physiological changes.

Byus et al (1987) found that ELF fields cause a significant increase in intracellular levels of ornithine decarboxylase (ODC), an enzyme necessary for cell growth. Agents which cause such an increase may, but do not necessarily, promote uncontrolled growth of tumor cells. The authors of the study suggest that exposure to 60-Hz ELF fields may serve as a tumor-promoting stimulus in the same way that certain chemical compounds do. Such agents are not initiators, that is, they do not cause damage DNA directly like ionizing radiation would. However, they may promote the growth of tumors already initiated.

Epidemiological studies

Epidemiological studies of abnormal reproductive outcome and increased cancer incidence are frequently cited in discussions of computers and health. As in any epidemiological study, these results are based on large groups of people, and are not predictive for any individual.

Epidemiological studies in which the reproductive outcomes of women using VDTs are compared to those of women not using VDTs offer mixed results. Several \"clusters\" of problem pregnancies in VDT users have been reported, but it has been argued that such small clusters are simply a result of statistical chance – that they could be found in any group of women, not just those using VDTs. It is also difficult to separate the efects of VDT use from other environmental factors and working conditions.

A study released in 1988 by the Northern California Kaiser Permanente Medical Care Program (Goldhaber et al, 1988) found that pregnant women who reported using VDTs more than 20 hours per week during the first trimester were significantly more likely to have miscarriages than women who performed similar work without using VDTs. Although the study has been criticized for relying on recall (the women reported their VDT use from memory), it is considered by many as the strongest study to date.

A more recent NIOSH study (Schnorr et al, 1991) found no increased risk of miscarriage among directory assistance operators who used VDTs during the first trimester compared with those who used LED or neon-glow tubes for similar work. However, this study has been criticized on two counts. First, it excluded very early miscarriages (those occurring in the first 14 days of pregnancy). This exclusion may be meaningful, since the risk of miscarriage decreases rapidly with gestational age, and since animal studies suggest that early stages of development may be particularly sensitive to electromagnetic signals. Secondly, while the overall VLF and ELF measurements near VDTs were higher than those surrounding the equipment used in the control groups, there was no difference between the two groups in the strength of the ELF field at abdominal level. Thus, the study could not determine whether fetal ELF exposure is associated with miscarriage. The primary author of the NIOSH study has confirmed this point and suggested that researchers concerned about ELF exposure look at other populations than the ones in her study (Branscum, 1991b).

The other set of epidemiological studies relevant to this topic are those examining cancer incidence in populations exposed to elevated VLF and ELF levels. Included in this set are studies reporting increased cancer incidence in populations such as electrical workers, ham radio operators, and children raised in houses near high tension electrical lines. These studies involve ELF exposure from sources other than VDTs, but they are often cited in conjunction with the VDT question and so will be mentioned here.

Pool (1990) reviews these studies, and points out that in some of them, job related exposure may include chemical carcinogens as well as ELF exposure, weakening the theory associating ELF with cancer. However, he concludes that although individual epidemiological studies may be criticized on one ground or another, as a group they have a consistency that is harder to ignore.

In another review, Nair and Morgan (1990) agree that although the studies associating ELF fields with cancer may be confounded by various other factors, the link seems real. They observe that the fact that ELF fields have been implicated as a promoter of cancer may be an important point. Thus, ELF exposure may promote the growth of a cancer that was originally triggered by some other factor.

What conclusions can be drawn?

Very few – there is no definitive answer yet to the question of how VLF or ELF exposure from computer use affects your health. While there is enough evidence of biological effects to raise the suspicion of human health hazards, the precise extent of the risk is unclear. As Nair et al (1989) phrase it in their OTA background paper: \"In our view, the emerging evidence no longer allows one to categorically assert that there are no risks. But it does not provide a basis for asserting that there is a significant risk.\"

To make matters even more difficult, the severity of some of the allegations has led to a certain amount of journalistic sensationalism. Some articles in the popular and computer press use attention-grabbing titles or strongly worded quotes to emphasize the seriousness of the risks. Others take the opposite approach, denying that any risks exist at all. This polarization is inaccurate and misleading; it offers a forced choice between a false sense of security or extreme panic.

What can I do?

Clearly, more research is needed, and it is in fact being carried out. In the meantime, here are some simple steps you can take if you are concerned about low frequency radiation from VDTs:

These suggestions can be characterized as prudent avoidance: strategies which can reduce your exposure to ELF fields without introducing extreme costs or inconvenience (Nair et al, 1989; Morgan and Nair, 1990). Of course, VDTs are just one source of ELF/VLF fields in the environment, but the principles of prudent avoidance can be applied to other sources as well.

What about special equipment?

A number of products have been introduced specifically in response to the controversy over radiation fields around VDTs. While some of these products are technically sound, others are simply marketing ploys.

Low-emission monitors

Several manufacturers have introduced low-emission monitors to the U.S. market. In some cases, these monitors were already being produced for the stricter European market; in others they were developed specifically in response to the controversy over VDT emissions.

Since magnetic fields are more difficult to block than electric fields, they have posed a greater problem for manufacturers of low-emission monitors. A couple of techniques can be used to decrease ELF magnetic emissions (O'Connor, 1991). In some models, the winding pattern of the deflection coils has been switched to a design (called a \"saddle-saddle coil\") in which all the windings are inside a ferrite band. Macworld's lab tests cited by O'Connor confirm that units using this design emit weaker ELF fields than units using the older (\"saddle-toroidal\") design. Other models use an additional series of wire coils to generate a magnetic field that cancels out the fields generated by the deflection coils. In the Macworld tests, a prototype monitor using canceling coils showed lower ELF magnetic fields than any other monitor tested (O'Connor, 1991).

If you are interested in purchasing a low-emission monitor, try to determine whether the monitor meets the Swedish guidelines for both VLF and ELF electric and magnetic fields. Ask specifically for information about ELF magnetic fields since they are harder to attenuate. (A few models marketed as low-emission do not meet the Swedish standard for ELF magnetic fields, although they do meet the VLF standards.) For independent measures of specific units, check computer journals for testing lab reports like those cited here.

Radiation shields and other devices

In addition to new low-emission monitors, some manufacturers have introduced products that claim to reduce electromagnetic exposure from existing VDTs.

Some of these products are of dubious worth. One company markets a five pound lead apron advertised as a shield against x-rays and extremely low frequency electromagnetic fields during VDT use. According to MacWeek, it provides no shielding at all of magnetic fields (Branscum, 1991a). (Note: Pregnant women should avoid lead aprons for daily use regardless of manufacturers' claims. According to Branscum, the Canadian Centre for Occupational Health and Safety warns that the use of such aprons is inappropriate and possibly hazardous.)

Other products have some merit, although not necessarily all that their manufacturers claim. There are, for instance, several screens on the market that purport to block electromagnetic fields from the front of the monitor. Sometimes these shields are marketed as combination antiglare-antiradiation screens. According to Macworld lab tests (Branscum, 1990), some of these screens do block VLF and/or ELF electric fields. However, none of the units tested so far can block magnetic fields.

If you are considering purchasing one of these shields, keep these results in mind. The shields may alleviate problems with glare. By reducing electric fields, they may also alleviate dust or allergy problems caused when static electric fields from the screen allow ions and pollutants to collect near the user's face. But if you are worried about magnetic fields, these shields will not reduce your exposure.

Macworld found one product that does reduce magnetic fields near VDTs. (Branscum, 1991a and O'Connor, 1991). This device is a steel-alloy cylinder that fits over the neck of the VDT's cathode ray tube. It is currently available only for certain models, notably the compact (nonmodular) Macintosh.

For most consumers, maintaining adequate distance from the monitor or purchasing a low-emission monitor are preferable alternatives to antiradiation shields.

Where can I read more?

Good sources for more information about electromagnetic fields and health include:

In the popular press, one of the strongest protagonists warning against exposure to electromagnetic fields is Paul Brodeur, whose book Currents of Death was serialized in The New Yorker:

If you read Brodeur's work, you should also read some contrasting points of view. One pertinent review of his book is:

As you read, the complexity and controversy of the issue will be evident. The answers may not be any clearer, but at least you will be as well-informed as possible so you may direct your actions accordingly.

Written by:
Janet Cottrell
University Computing Services
University of Vermont
October 28, 1991


References

ACGIH, 1991. Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. ISBN: 0-936712-92-9. Cincinnati: ACGIH.

Branscom, Deborah. 1990. Conspicuous Consumer: Comfortable computing. Macworld. July, 1990: 71-88.

Branscom, Deborah. 1991a. Buyer Beware: Radiation finds its niche as a marketing tool. Macworld. February, 1991: 83-92.

Branscom, Deborah. 1991b. Electromagnetic Update: The controversy – and research – continues. Macworld. October, 1991: 65-70.

Brodeur, Paul. 1989. Annals of Radiation: The hazards of electromagnetic fields. The New Yorker. Three-part series: June 12, 1989 pages 51-88; June 19, 1989, pages 47-73; and June 26, 1989, pages 39-68.

Brodeur, Paul. 1990. The magnetic-field menace. Macworld. July, 1990: 136-145Byus, Craig V., Pieper, Susan E. and Adey, W. Ross. 1987. The effects of low-energy 60-Hz environmental electromagnetic fields upon the growth-related enzyme ornithine decarboxylase. Carcinogenesis (London) 8(10): 1385-1390.

Byus, Craig V.; Pieper, Susan E.; and Adey, W. Ross. 1987. The effects of low-energy 60-Hz environmental electromagnetic fields upon the growth-related enzyme ornithine decarboxylase. Carcinogenesis (London) 8(10): 1385-1390.

Carlson, Kyla K. 1991. VLF emissions from monitors: You be the judge of safety. Infoworld, September 2, 1991, page 58.

Chandler, Doug. 1991a. Low-emission monitors are crossing the Atlantic. PC-Week. July 18, 1991, page 105.

Chandler, Doug. 1991b. Studies provide inconclusive findings about dangers of monitor emissions. PC-Week. July 18, 1991, page 105-113.

Charron, David. 1988. Health hazards of radiation from video display terminals: Questions and answers. Hamilton, Ontario: Canadian Centre for Occupational Health and Safety. (CCOHS #P86-19E.)

Copeland, Ron. 1990. VLF radiation emission levels vary widely among popular PC monitors. Infoworld, November 12, 1990, page 74-83.

Coughlin, Francie. 1991. Low-emission color monitors. PC-Week, July 8, 1991, page 108.

Damore, Kelley. 1991. San Francisco law takes first step on safety issue. PC-Week. January 28, 1991, page 19.

Delgado, Jose; Leal, Jocelyne; Monteagudo, Jose Luis; and Gracia, Manuel Garcia. 1982. Embryological changes induced by weak, extremely low frequency electromagnetic fields. Journal of Anatomy. 134 (3): 533-551.

Fitzgerald, Karen. 1990. Electromagnetic Fields: The jury's still out. Part 2: Societal reverberations. IEEE Spectrum, August, 1990: 27-32.

Goldhaber, Marilyn K.; Polen, Michael; and Hiatt, Robert. 1988. The risk of miscarriage and birth defects among women who use visual display terminals during pregnancy. American Journal of Industrial Medicine 13: 695-706.

Goodman, Reba, and Henderson, Ann. 1988. Exposure of salivary gland cells to low-frequency electromagnetic fields alters polypeptide synthesis. Proceedings of the National Academic of Sciences. 85: 3928-3932.

Marha, Karel. 1983. VLF - Very Low Frequency Fields Near VDTs and an Example of Their Removal. Hamilton, Ontario: Canadian Centre for Occupational Health and Safety. (CCOHS #P86-19E.)

Marha, Karel; Pathak, Bhawani; and Charron, David. 1986. Emissions from Video Display Terminals and their Measurement: A Training Manual. Hamilton, Ontario: Canadian Centre for Occupational Health and Safety. (CCOHS #P86-19E.) 42 pages.

Morgan, Granger and Nair, Indira. 1990. Electromagnetic Fields: The jury's still out. Part 3: Managing the risks. IEEE Spectrum August, 1990: 32-35

Nair, Indira M. and Morgan, M. Granger. 1990. Electromagnetic Fields: the Jury's Still Out. Part 1: Biological effects. IEEE Spectrum. August, 1990: 23-27.

Nair, Indira; Morgan, M. Granger; and Florig, H. Keith. 1989. Biological Effects of Power Frequency Electric and Magnetic Fields. Background Paper prepared for U.S. Congress Office of Technology Assessment, OTA-BP-E-53. GPO stock number 052-003-01152-2. Washington, D.C.: U.S. Government Printing Office. 103 pages.

O'Connor, Rory J. 1991. Seeking ELF relief. Macworld. October, 1991, pages 124-129.

Pool, Robert. 1990 Electromagnetic Fields: The Biological Evidence. Science 249: 1378-1381.

Sauda, Michael. 1991a. Maine's VDT Operator Safety Law. Posted to the Bitnet SAFETY list, March 25, 1991.

Sauda, Michael. 1991b. Personal communication.

Schnorr, Teresa; Grajewski, Barbara; Hornung, Richard; Thun, Michael; Eceland, Grace; Murray, William; Conover, David; and Halperin, William. 1991. Video display terminals and the risk of spontaneous abortion. New England Journal of Medicine, 324 (11): 727-733.

Steere, Leslie. 1991. S.F. monitors workers' health. Publish. March, 1991, page 19.

Ubeda, Alejandro; Leal, Jocelyne; Trillo, Maria; Jimenez, Maria; and Delgado, Jose. 1983. Pulse shape of magnetic fields influences chick embryogenesis. Journal of Anatomy. 137 (3): 513-536.

Updegrove, Daniel. 1991. San Francisco Worker Safety Ordinance, December 1990. From the articles database of CCNEWS, the Electronic Forum for Campus Computing Newsletter Editors, a BITNET-based Service of EDUCOM.


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