Safety Guide for Experiments at CERN
Part III - Advice
42. Magnetic Fields
Possible direct biological effects from magnetic fields, and in particular from pulsed or A.C. fields, cannot be excluded, but the present state of knowledge of the effects on human beings is limited. Studies on workers exposed to magnetic fields have indicated various subjective symptoms and functional disturbances like fatigue, disturbed electrocardiogram and changes in heart rhythm, loss of appetite, irritation or tingling sensations of the skin. No significant long term effects have been noticed so far. In the present situation, it is advisable to reduce work in high magnetic fields to a minimum.
- Medical risks
- Technical Hazards
- Warning Signs
42.1 - Medical risks
Persons wearing metallic implants, such as bone or articular prostheses, surgical
clips, nails or screws in broken bones, or even dental fillings may feel painful
Persons fitted with pace-makers encounter a specific risk as static or pulsed
magnetic fields may influence the good working order of their pace-makers. For
these persons, the exposure limit of 0.5 mT (0.5 milliTesla = 5 Gauss) must
be strictly observed.
42.2 - Technical Hazards
A danger frequently encountered comes from loose ferro-magnetic objects present
in a static magnetic field. If the field is strong enough, it will attract such
objects from quite a distance and cause them to fly along the field lines towards
the magnet. Watch out for any ferro-magnetic objects you may carry in your pockets.
Particularly objects with sharp edges may become dangerous projectiles. The use
of ferro-magnetic objects shall therefore be excluded from any magnetic field.
Non-ferro-magnetic tools are available commercially.
Various electronic equipment and magnetic data carriers may be affected by
magnetic fields. For cathode ray devices and photo-multiplier tubes such effects
start to be noticeable already at 0.2 mT. Cardiac pace-makers, computers, magnetic
storage media, credit cards and analogue watches (particularly mechanical) may
be affected in fields above 0.5 mT.
Dynamic magnetic fields cause induced voltages, and the resulting currents
either cause heating of metallic objects or disturbances in the human nervous
42.3 - Warning Signs
Stray field zones must be adequately labelled and fenced off if necessary. See
Safety Code A
3, ("Safety Colours and Safety Signs") and Safety
Instruction IS 36 Rev. ("Use of Static Magnetic Fields at CERN"). Particular
attention should be given to warning persons with pace-makers and metal implants.
See also Section 5.4.5 for limiting values of exposure.