5.3 Posting Requirements for Magnetic Field Warning Signs
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Installation Planning Guide
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5.3 Posting Requirements for Magnetic Field Warning Signs
The strong magnetic fields that surround a superconducting magnet are capable of causing
death or serious injury to individuals with implanted or attached medical devices such as
pacemakers or prosthetic parts. Such fields can also suddenly pull nearby magnetic tools,
equipment, and dewars into the magnet body with considerable force, which could cause
personal injury or serious damage. Moreover, strong magnetic fields can erase magnetic
media such as tapes and floppy disks, disable the information stored on the magnetic strip
of automated teller machine (ATM) and credit cards, and damage some watches.
To warn of the presence and hazard of strong magnetic fields, the customer is responsible
for posting clearly visible signs warning of magnetic field hazards. This responsibility
includes measuring stray fields with a gaussmeter.
Radio-frequency emissions may also pose a danger to some individuals. The rf emission
levels from Varian NMR equipment have been measured and compared to the IEEE/ANSI
C95.1-1991 standard. For further information, refer to the RF Environment section of the
Installation Planning Guide.
Warning Signs
Varian provides signs to help customers meet this posting responsibility. These signs must
be posted according to the following requirements before the magnet is energized:
1.
10-gauss warning signs (
Figure 8
) – Post along the 10-gauss perimeter of the magnet
so that a sign can be easily seen by any person about to enter the 10-gauss field from
any direction. Refer to the manuals supplied with the magnet for the size of a typical
10-gauss stray field. Check this gauss level after the magnet is installed.
Note that the stray field may extend vertically to adjacent floors, and additional signs
may be needed there. A sign is not required if the 10-gauss field extends less than 30
cm (12 in.) beyond a permanent wall or less than 61 cm (24 in.) beyond the floor
above the magnet.
2.
5-gauss warning signs (
Figure 9
) – Post along the 5-gauss perimeter of the magnet
so that a sign can be easily seen by any person about to enter the 5-gauss field from
any direction. Refer to the manuals supplied with the magnet for the size of a typical
5-gauss stray field. Check this gauss level after the magnet is installed. Note that the
stray field may extend vertically to adjacent floors, and additional signs may be
needed there.
