Chapter Twelve - Magnetic Fields

Stray Field Safety

Superconducting magnets are capable of generating very strong magnetic fields.  These fields are not necessarily confined entirely to the high field region in the core of the magnet.  Stray or fringe fields from a magnet frequently expand out in areas where personnel operate - posing potential hazards which can not be ignored.

Cardiac pacemakers and other implants are one of the most significant hazards in a magnetic field for obvious reasons.  CHESS personnel or visitors with these devices should take extreme caution to avoid magnetic fields above five gauss.  Since superconducting magnets at CHESS are housed in the CESR tunnel, casual visitors to CHESS are at the least risk of being exposed to significant stray fields.

Many types of instrumentation and media are also sensitive to magnetic fields.  Oscilloscopes and other CRT based instruments can experience distortions and/or color separations as a result of stray fields.  These distortions, if they are serious enough or if they are left uncorrected for a long period of time, can permanently damage the instrument.  Magnetic storage media such as floppy disks, hard disks, or magnetic tapes can also be erased by stray fields.

Other instrumentation frequently contain magnetic relays which may also be affected by magnetic fields.  Most instruments do not contain magnetic shielding.

Magnetic tools must be considered as well.  These can become ballistic items which are a physical threat if they are allowed too close to a charged magnet.

If at all possible, in choosing a site for your superconducting magnet, you should pick or design a site which is as far away as possible from hallways and doors, or walls, floors and ceilings shared with other labs.  Locate control instrumentation and aisles as far away from the magnet as possible to minimize traffic in the area.  This will minimize risk to personnel both in your lab and in others.  Also, be sure to post warning labels on all doors which enter the lab so unwary visitors are properly informed.  A basket just inside the lab door for wallets and watches is a common practice, too.

Last Update: 2006-09-21