Biological Effects of Magnetic Fields
Effects are broken into two broad groups: physical effects where mechanical action occurs and biological effects that occur at the chemical and cellular level.
Physical Effects of Static Fields
By far the most important effect here is from the attraction of magnetic objects in or on the body by the magnetic field. Objects such as pacemakers, surgical clips and implants, clipboards, tools, jewelry, watches, mops, buckets, scissors, screws, etc. have all been documented as being potential hazards. Even low mass items can become hazardous when moving at high speed. Magnetic objects will try to align themselves with the magnetic field lines. If an implanted object tries to do this, the torquing may cause serious injury.
Modern pacemakers are designed to be tested or reprogrammed with the use of a small magnetic external to the body. Static fields can close reed switches and cause the pacemaker to enter test, reprogram, bypass, etc. modes with possible injury.
Because there are no regulatory limits and much biological data is unclear, the most conservative limits from recognized organizations will be used. Limits are primarily from the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLV) data. The International Radiation Protection Association (IRPA) published a guide in 1990 and is used here.
Magnetic Static Field Exposure Limits
- Routine occupational exposures should not exceed 60 mT (600 G) to the whole body on an 8 hr time weighted average.
- Routine occupational exposures should not exceed 600 mT (6000 G) to the extremities on an 8 hr time weighted average.
- A maximum ceiling (i.e. maximum value at any time) should be 2 T for the whole body and 5 T for the extremities.
- Pacemaker users or others with magnetic implants should not exceed 0.5 mT (5 gauss) at any time.
General Safety Consideration
The obvious safety action is to prevent any magnetic material from entering the work area. Because the hazard from flying objects depends on many factors, users must be continuously watchful. Do not underestimate the rapid increase in field strength as one approaches the source; a gradual pull may not always be felt first. Please be sure that your magnet will not generate a hazard area or affect equipment outside your work area.