Magnetic Fields

Dangers from Magnetic Fields

Superconducting magnets may generate extremely strong fields. Although the field is strongest in the bore of the magnet, there may be a strong stray field. The stray field increases greatly nearer to the magnet; magnetic objects may fly suddenly into the magnet causing injury or even death.

In the Liquids Magnetic Resonance labs, 5 and 10 gauss lines are marked on the floors. Other researchers with strong magnets must post warnings on the door. Do not situate magnets where the stray field will pass through a wall into a corridor.



Users with pacemakers should not enter the magnetic resonance labs without first consulting their physician. The magnetic field may not interfere with valves but radio frequency pulses may disrupt the pacemaker timing.


Implants and Metal Prosthetics

People with surgical implants should not go inside the 5 gauss line without prior consultation with their physician. Implants may torque causing pain or internal bleeding.


Magnetic Objects

Magnetic objects may be pulled strongly into the magnetic field. A flying object may hit someone or a sharp object may slice off fingers. Large objects like gas cylinders may strike with fatal force. Do not attempt to pull objects that have been pulled onto the magnet; the object may shift, pinching fingers.


Credit Cards and Watches

Credit cards, library cards, TTC passes, or any card with a magnetic stripe may be damaged by the magnetic field. Leave them outside the 10 gauss line. Watches may be stopped or permanently damaged by the field. Leave analog watches outside of the 10 gauss line.



Quenching occurs when there is a fast boil off of liquid helium. Sudden quenches of superconducting magnets may displace oxygen in a laboratory. Leave the room immediately if a quench occurs.



  • Do consult your physician before entering a magnetic resonance lab if you have any reason to suspect you may be affected. 
  • Do leave magnetic objects outside the magnetic resonance labs. 
  • Do leave the laboratory if a sudden quench occurs.


  • Do not enter a room with magnetic resonance equipment if you wear a pacemaker. 
  • Do not bring any magnetic or ferrous object within the 10 gauss line of a magnet. 
  • Do not bring a compressed gas cylinder within the 5 gauss line of a superconductor magnet.
  • Do not bring magnetic stripe cards or watches into the 10 gauss field.