Chapter Twelve - Magnetic
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.