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      This page contains important safety information. Please take the time to read it before entering the NMR laboratories.

Magnetic Fields

      The NMR spectrometers incorporate superconducting magnets, which exert a very high magnetic field. This field is so strong that it can pull metal objects to the magnet (eg, take a spanner from your grasp) if they are within the safe operating distance, otherwise known as the 5 Gauss Line. The closer to the magnet, the larger the force, which can come as a surprise. Therefore, all metal objects must be kept as far away from the magnet as possible.
      A metal object becoming attached to the magnet would be a great inconvenience (it would disrupt the shimming and therefore lineshape radically; to remove it would require bringing the magnet off field, at great expense).
      However, not only would it be inconvenient, it would be very dangerous. A metal object near the magnet can disrupt the field around a localised region of the superconducting coil. This can lead to localised heating of that area of coil, causing the superconducting wire in the coil to lose superconductivity and become normal. The increased resistivity of the now normal wire will heat the helium, causing a chain reaction which heats all the helium in the magnet almost at once, changing it from liquid to gas. When this happens, the gas expands dramatically in volume, causing risks of asphyxiation as it leaves the magnet and fills the room (very quickly). This  whole process is known as a quench.

In the event of a quench

  • Leave the room immediately and ensure nobody else enters the room.
  • Sound the fire alarm and leave the building.
  • DO NOT RE-ENTER THE ROOM until the NMR staff declare it safe.
  • DO NOT RE-ENTER THE BUILDING until the NMR staff and/or safety officers declare it safe.
  • If you can see somebody is incapacitated in the room, if possible break a window to allow oxygen into the room, but DO NOT RE-ENTER THE ROOM as you must ensure your own safety.
Helium is inert, but it is an asphyxiant and large quantities can displace oxygen in a confined space. Please read this document for the risks and safety procedures associated with helium and other cryogens.

How would I spot a quench?

      A quench warranting evacuation would be obvious by the noise of the escaping gas and clouds of vapor. Oxygen depletion alarms and helium detectors are fitted in the room, but even if these are not sounding, leave the room following the above procedures if a quench occurs.

Pacemakers, Medical Implants and Prosthetic Devices

      Cardiac pacemaker wearers must remain outside the 5-gauss perimeter from the magnet until safety is clearly established. An NMR superconducting magnet generates strong magnetic and electromagnetic fields that can inhibit operation of some cardiac pacemakers, which could result in death or serious injury to the user.
      Consult the pacemaker user’s manual, contact the manufacturer, or confer with a physician to determine the effect on a specific pacemaker.
      Overall, it is advisable that those with pacemakers, medical implants (clips, stents) or other prosthetic devices do not enter the room at all without prior consultation with the NMR staff.
      Here is a list of some potentially unsafe implants etc.;
  • Cardiac pacemakers
  • Implanted defibrillators, neurostimulators and insulin pumps
  • Swan Ganz catheters
  • Orbital (in the eye) metallic foreign bodies
  • Any intravascular coils, filters or stents (some may be compatible)
  • Cochlear implants (possible compatibility)
  • Aneurysm clips (possible compatibility
Are Magnetic Fields Safe?

      Some publications (1) suggest that long term cumulative large exposures to oscillating magnetic fields (60 Hz) may be associated with increased incidence of brain cancer in power industry workers.  However, the cumulative doses for an effect were large, and represent no hazard outside the 5 gauss safety line normally used with NMR magnets.
      Others (2) believe that while more research needs to be done on the topic, "an analysis of the interaction mechanisms suggests that short-term health effects can be predicted and so avoided." Therefore, we recommend that the 5 gauss limit is crossed only for sample changing or for probe maintenance, and for a minimal amount of time. 

Bank Cards, Watches, Mobile Phones

      One would advise a comonsense approach towards approaching a superconducting magnet with items which can be influenced by magnetic fields, such as bank cards, phones, watches (digital, battery-operated and wound), calculators, laptops and PDAs. These can be permanently damaged by the magnetic fields. Therefore, do not approach the magnets with these items. If you do, it is your own responsiblilty, and the CSCB and the School of Chemistry and Chemical Biology and their staff accept no responsibility or liability caused by such actions.

Care with Samples

      Do not exceed the boiling or freezing points of your sample. A sample subjected to a temperature change can build up excessive pressure which can break the tube. Broken glass, projectiles and hot or toxic chemicals can cause injury. To avoid this hazard, establish the freezing and boiling points of a sample before doing a variable temperature experiment, and never rapidly heat or cool a sample. Always wear safety glasses near the magnet when performing variable temperature experiments.
Care with Spinners

      Please take care while putting a sample in a spinner. Be very careful with sample tubes as they are fragile and break easily. If you break the tube, you may hurt yourself, and possibly contaminate your wound with chemicals. Please seek help from a first-aider if this happens.
      Please take care with the spinners also, as they are precision-milled and are very expensive. If you accidentally drop one, inform one of the NMR staff, otherwise use of this spinner may affect your or a colleague's data. 

If a Tube Breaks in the Magnet

      If a sample tube breaks in the NMR magnet, inform the NMR staff immediately. The tube must be removed immediately by trained staff in a safe manner to avoid damage to the probe, which is expensive. The NMR staff recognise that accidents can happen.

Sample Tube Storage

Sample tubes must be stored carefully, and not subjected to long heating/drying as this will warp the tube, potentially causing damage to the NMR spectrometer probe. NMR tubes must be replaced periodically (every six months or so) as they do deteriorate with usage.


      Liquid Nitrogen and Liquid Helium are routinely used within the NMR laboratories to keep the magnets at superconducting temperatures. When the magnets are being filled with these materials, no-one other than trained NMR or technical staff may enter the room, as there are risks of cryogenic burns and/or asphyxiation.

      Please read this document to appraise yourself of the risks associated with cryogens.

1. David A. Savitz and Dana P. Loomis (1995). "Magnetic field exposure in relation to leukemia and brain cancer mortality among electric utility workers." Am. J. Epidemiology 141(1), 123-134.
2. A.F. McKinlay, M.H. Repacholi (2005). "More research is needed to determine the safety of static magnetic fields." Progress in Biophysics and Molecular Biology 87, 173–174