Estimated exposure to static magnetic fields for the staffs of NMR-units

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.