Abstract
An industrial hygiene survey concentrating on static magnetic field hazards was conducted at several nuclear magnetic resonance (NMR) facilities, including research laboratories and a clinical magnetic resonance imaging (MRI) center. The strongest magnetic fields routinely accessible to NMR staff were found to be 1.0 tesla for the torso and 4.7 tesla for the arms, due to a wide-bore research magnet. Estimates of typical exposure levels of NMR workers were made on the basis of fringe field measurements and observations of work practices. Estimated 8-hour time-weighted average (TWA) exposures ranged from 1.5 to 64.0 millitesla; duration of high field exposure was the major factor determining the TWA. People working for extended periods in close proximity to wide-bore superconducting magnets were exposed to static magnetic fields near or exceeding the threshold limit value of 60 millitesla for the whole-body TWA. Peak exposure to the extremities exceeded ceiling limits. No evidence exists for adverse health effects at current exposure levels. Controls on work practices are recommended as the most practical means of reducing exposure.