Magnetic Fields

Magnetic fields refer to a nuclear magnetic resonance (NMR) system or a magnetic resonance imaging (MRI) system. The purpose of the static magnetic field safety program is to ensure superconducting magnets and liquid cryogens are stored and used properly.

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommends limits for controlling exposures to static magnetic fields.  The limits are based on careful review of the research into the health effects of exposure to static magnetic fields. The Brown University magnetic fields safety program follows these guidelines (limits).

To learn more about non-ionizing radiation, click the 'Compliance' and 'Resources’ tabs to the left.

Superconducting Magnets

Strong magnetic fields are created by superconducting magnets. These fields can affect ferromagnetic objects and surgical implants, so precautions must be taken when you are near an NMR.

Attractive forces are exerted on ferromagnetic materials brought in close proximity to a superconducting magnet. The force may become large enough to move objects uncontrollably towards the magnet. For this reason, do not take ferromagnetic objects near an NMR as it may result in damage to the magnet/probes and/or possibly resulting in a serious injury.

Static and oscillating magnetic fields may affect medical implants. If you have a medical implant (electronic, clips, prostheses) and wish to enter an NMR or MRI lab, notify the lab supervisor first.

Cryogen Hazards

Cryogens such as liquid nitrogen and liquid helium, which are present in the magnet cryostat and portable dewars, have the following risks associated with them: asphyxiation, frostbite and chemical explosion.


When a magnet quenches, or suddenly becomes non-superconducting, large amounts of liquid cryogens are quickly vaporized. Due to their large expansion ratios (nitrogen 695:1, helium 760:1), these gases can quickly displace all the oxygen in the NMR room and cause asphyxiation. Effects from oxygen deficiency become noticeable at levels below ~18% and sudden death may occur at ~6% oxygen content by volume. If you observe a sudden exhaust of gas from a magnet (and NMR staff are not performing a cryogen fill) exit the NMR laboratory immediately and notify the Department of Public Safety (401-863-4111).


Direct contact with cryogenic substances in liquid or vapor form can produce “cold burns” on the skin similar to conventional burns.  The temperature of liquid helium is -269 celsius (C) and that of liquid nitrogen is -196 C.  When handling cryogens, individuals must wear the proper personal protective equipment (gloves, goggles, long pants and closed toe shoes).

Chemical Explosion

Cryogenic fluids with a boiling point below that of liquid oxygen are able to condense oxygen from the atmosphere. Repeated replenishment of the system can thereby cause oxygen to accumulate. Violent reactions (e.g. rapid combustion or explosion) may occur if the materials that make contact with the oxygen are combustible. To reduce the risk of asphyxiation or explosion, ensure proper ventilation where cryogens are stored or used.