| 1. |
- Jonsson, P., et al.
(author)
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Estimated exposure to static magnetic fields for the staffs of NMR-units
- 1996
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In: Occup Med (Lond). ; 46:1, s. 17-9
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Journal article (peer-reviewed)abstract
- Exposure of the staffs to static magnetic fields of NMR-units, was investigated at two departments for chemical analysis (static field strength of the systems 11.7 and 4.7 Tesla) and two for clinical imaging (0.5 and 0.02 Tesla). The exposure time was estimated by personal interviews. The magnetic flux density was highly dependent on distance to the magnet, and the magnetic fields in normal work with the NMR-units were, during most working time, lower than 1 milliTesla (mT), which is far below the whole-body limit recommended by the American Conference of Governmental and Industrial Hygienists (60 mT), the British National Radiation Protection Board (200 mT), or the international Commission on Non-Ionizing Radiation Protection (200 mT). During short periods, when changing samples or assisting anxious patients, the fields may be strong (100-150 mT). The recommended ceiling values (2-5 Tesla) are, however, not exceeded.
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| 2. |
- van der Woord, M. P., et al.
(author)
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Within-day variability of magnetic fields among electric utility workers: consequences for measurement strategies
- 2000
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In: Aihaj. ; 61:1, s. 31-8
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Journal article (peer-reviewed)abstract
- Occupational exposure to 50-Hz magnetic fields was surveyed among electric utility workers to investigate (1) components of exposure variability, (2) patterns of autocorrelation between short-term measurements, and (3) imprecision and misclassification due to short-term measurements. Spot measurements every 10 seconds during 81 working days were analyzed for 42 electric utility workers from 10 occupational subgroups and during 8 working days for 4 office workers from the same company. For the 8-hour time-weighted average (TWA) magnetic fields, the variability was partitioned into its components: within workers, between workers, and between groups. For spot measurements of magnetic fields, the within-day variance component also was examined. Autocorrelation functions were determined and numbers of short-term measurements necessary for reliable estimates of 8-hour TWA magnetic fields were assessed. Spot measurements of magnetic fields, as well as 8-hour TWA magnetic fields, were approximately lognormally distributed among workers. The mean exposure to magnetic fields was 0.47 microT (n = 81 days) in electric utility workers and 0.12 microT (n = 8 days) in office workers. A large fraction, 76% of the spot measurements total variance, could be attributed to variability within days. For the 8-hour TWA magnetic fields, between-group variability was small and of the same magnitude as between-worker variability. Significant autocorrelations between short-term averages of 7.5, 15, and 30 minutes were present, when taken within periods of 30 minutes. One-hour averages showed no autocorrelation. Simulations showed that, due to high within-day variability and autocorrelation, a limited number of short-term measurements of magnetic fields in electric utility workers are likely to result in imprecise estimates of 8-hour TWA magnetic fields. Measurement strategies relying on short-term (spot) measurements are therefore likely to result in misclassification of exposure and consequently absent or spurious exposure-response relations.
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