Video Displays, Work, and Vision (1983) / Chapter Skim
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3. Radiation Emissions and Their Effects
3. Radiation Emissions and Their Effects
Pages 44-65
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From page 44... ...
The radiation emissions of a wide variety of different types of VDTs have been measured, and most types of VDTs in current use have been adequately surveyed for all types of potentially hazardous electromagnetic radiation. In many cases, measurements were undertaken because of concerns expressed by VDT users about potential radiation hazards.
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From page 45... ...
Some differences appear in the levels of radiation reported in different studies (see Table 3.1~; the largest differences occur between field surveys and laboratory studies. In the field studies reviewed, VDTs and measuring instruments were not shielded from ambient radiation; thus, the readings obtained represent the sum of the VDT emissions and all other sources of radiation present.
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From page 46... ...
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From page 48... ...
Because the values obtained for the emissions of all types of radiation measured were considerably below currently recommended occupational exposure standards, NIOSH concluded that "the VDTs surveyed do not appear capable of producing levels of radiation presenting an occupational ocular radiation hazard" (Moss et al., 1977:14~. The Bell Telephone Laboratories Study The next widely circulated, published radiation survey was conducted by Weiss and Petersen (1979)
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From page 49... ...
_ fin 1967 national attention was drawn to the emission of X radiation from color television receivers. Some color televisions and some VDTs in use at that time used high-voltage shunt regulators that emitted higher than acceptable levels of X radiation (see Bureau of Radiological Health, 1981:6~;theshunt regulators were redesigned to reduce radiation leakage.
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From page 50... ...
X-ray emissions were 1/50 of the British emission standard for household electronic products, UV emissions were 1/100 of permissible limits, visible and near infrared emit signs were 1/25 and 1/2,000 of applicable limits, and RF intensities were 1/10 of the appropriate standard limit values in most cases. Based on the measured levels of emission and standards for exposure, the study concluded that the "radiation normally emitted from a VDU [a VDT]
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From page 51... ...
Potential sources of emissions were carefully analyzed, and measurements were made under controlled laboratory conditions. The emission levels of all bands of ionizing and nonionizing radiation were well below current state, federal, and international standards and guidelines for exposure for all 34 of the units tested in this study.
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From page 52... ...
As noted above, however, field studies do not accurately measure the actual emission levels; laboratory studies indicate that VDT emissions of X radiation are usually orders of magnitude below 0.5 mR/h. The booklet also expressed concern that the X-radiation standard did not consider risks of biological damage other than "fatal radiation-induced cancer." In fact, radiation standards are generally based on all known serious biological effects, both acute and long term, and take into consideration the cumulative exposure of workers to various human-made and natural sources of radiation.
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From page 53... ...
Radio frequency radiation emissions from VDTs, averaged over the 1 kHz to 300 GHz frequency range, have been reported to be of the order of the ambient levels produced in metropolitan areas by radio, television, and communications transmitters (Wolbarsht et al., 1980)
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From page 54... ...
The level of ionizing radiation generally believed to significantly increase the risk of birth defects in humans is more than 1 red for acute exposure. For comparison, one may consider that, on the average, people in the United States receive a total dose from natural and human-made sources of about 60 mrad (0.06 red)
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From page 55... ...
Visible and Infrared Radiation Ocular effects from visible and near-IA radiation are largely limited to the retina, where the radiation is focused. Visible radiation levels required to cause retinal injury are lowest at 440 nm (blue light)
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From page 56... ...
criteria document on microwave and RF fields concluded that human occupational exposure to RF and microwave fields between 0.1 and 1.0 mW/cm incorporated a sufficient safety factor so as not to lead to adverse effects. Skin Rashes Several incidents of skin rash (especially face rashes)
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From page 57... ...
Lens opacities involving the central axis of the lens that are sufficient to degrade the optical image and to reduce visual acuity are considered abnormal. Small, inconsequential opacities in the lens are extremely common; many are probably congenital.
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From page 58... ...
were actually inconsequential opacities that did not appreciably reduce visual acuity. Of the four patients with significant lens opacities: · One had been a radar technician for 15 years and had required cataract surgery on his right eye long before he had ever
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From page 59... ...
Since many people have lens opacities and many people use VDTs, it is hardly surprising that some VDT users have lens opacities. As VDT use increases, so, inevitably, will the number of people with cataracts who use them.
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From page 60... ...
Methods of ! Studying Whether There is a Relationship Between VDT Use and Cataracts The question is not whether VDT users can also have lens opacities or cataracts, but whether VDT use increases the risk of developing a cataract.
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From page 61... ...
Both concurrent and nonconcurrent longitudinal studies pose problems: It is generally impractical to randomly assign workers to use or not use VDTs, and one cannot eliminate the possibility of confounding variables (bias) in any matched sample.
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From page 62... ...
Because diabetics are already at increased risk of developing cataracts, a study of this sort might demonstrate that VDT users had a higher rate of cataract development than nonusers, not because users were exposed to VDTs, but because they contained a larger proportion of diabetics. More generally, a practical, standardized, reproducible method for demonstrating and quantifying the presence of lens opacities is yet to be developed, complicating the diagnosis and comparison of "cataract" rates in population groups.
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From page 63... ...
The NIOSH Baltimore Sun Study The Baltimore Sun VDT study was carried out by NIOSH Appendix B includes a detailed review of the preliminary results of this study)
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From page 64... ...
Perhaps of equal importance, the emission levels from VDTs are far below those emitted by many common electronic products or those present from natural sources in the environment (Smith and Brown, 1971; United Nations Scientific Committee on the Effects of Atomic Radiation, 1977; World Health Organization, 1979; National Research Council, 1980; Sliney and Wolbarsht, 1980~. Even if a large number of VDTs were arranged near each other in an office, the summed levels of radiation would be less than ambient levels of radiation from other sources.
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From page 65... ...
65 more definitive studies of cataracts among VOT users are likely to prove productive. Until that time' however, because of the lack of evidence suggesting a real association between VDT use and visually dishing cataract, and the extraordinary sing complexity, and cost of the definitive study needed to disprove the possibility of such an association' it would seem unreasonable and uniustif~ble to embark on such studies.
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