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Magnet Safety: Continuous Exposure Limits Guidelines

Consider the guidelines below when evaluating standards for continuous static magnetic field exposure for the magnets operating in your lab.

Superconducting magnets used for nuclear magnetic resonance (NMR) spectroscopy are the source of powerful static magnetic fields.

There are no known adverse biological effects in static magnetic fields within the exposure values established by the American Conference of Governmental Industrial Hygienists (ACGIH).

ACGIH emphasizes that: "These values should be used as guides in the control of exposure to static magnetic fields and should not be regarded as fine lines between safe and dangerous levels." 1

An international committee is currently reviewing the issue of exposure and occupational safety. Until further information becomes available, use your best judgment and conservative practices.

ACGIH threshold limit values for continuous exposure to static magnetic fields

Abbreviations used in this table:
G – Gauss; a unit of magnetic field intensity, equal to 0.0001 Tesla
mT – millitesla
T – Tesla; magnetic field strength is measured in Tesla
TWA – time weighted average

Note: 1 Gauss (G) = 0.1 millitesla (mT)
5 G (0.5mT) Highest allowed field for implanted cardiac pacemakers
10G (1.0mT) Damage to watches, credit cards, magnetic tape, and computer disks
30G (3.0mT) Kinetic energy hazard from small ferrous objects
600 G (60mT) Allowed TWA for routine exposure (whole body) (8-hour TWA*)
6000 G (600mT) Allowed TWA for routine exposure (extremities) (8-hour TWA*)
20,000 G (2T) Whole body ceiling limit (no exposure allowed above this limit)
50,000 G (5T) Extremity ceiling limit (no exposure allowed above this limit)
* TWA exposure time is normally a concern only for extremely high field exposures to the whole body.

1 2003 TLVS® and BEIs® based on the "Documentation of the Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices," ACGIH Worldwide, p. 142.

Questions? Contact EH&S Radiation Safety, (858) 822-2494.