Control of magnetic field areas

For the safety of people in the general vicinity of an MRI magnet, a controlled area is usually declared as defined by the 0.5 mT (5 Gauss) line. Magnetic fields higher than 0.5 mT should not be exceeded in a public area. Barriers, access control doors, warning signs and facilities for the safe keeping of watches, credit cards and other magnetically sensitive objects must be provided.

Further reduction of the fringe fields to 0.1 mT or even 0.05 mT (less than 1 Gauss) may be necessary to safeguard the performance of sensitive equipment such as computer monitors, image amplifiers and other medical equipment etc., or to satisfy local regulations.
For comparison, the magnetic field strength of the earth is approximately 0.04 mT (0.4 Gauss).

Picture above: Example of a fringe magnetic field