Chemical Services, NMR Unit
High-Resolution NMR Facility
There are some important safety considerations which one should be familiar with before using a NMR spectrometer. These concern the use of strong magnetic fields and cryogenic liquids.
Magnetic fields from high field magnets can literally pick up and pull ferromagnetic items into the bore of the magnet. Caution must be taken to keep all ferromagnetic items away from the magnet because they can seriously damage the magnet, shim coils, and probe. The force exerted on the concentric cryogenic dewars within a magnet by a large metal object stuck to the magnet can break dewars and magnet supports. The kinetic energy of an object being sucked into a magnet can smash a dewar or an electrical connector on a probe. Small ferromagnetic objects are just as much a concern as larger ones. A small metal sliver can get sucked into the bore of the magnet and destroy the homogeneity of the magnet achieved with a set of shim settings.
There are additional concerns regarding the effect of magnetic fields on electronic circuitry, specifically pacemakers. An individual with a pacemaker walking through a strong magnetic field can induce currents in the pacemaker circuitry, which will cause it to fail and possibly cause death. A person with a pacemaker must not be able to inadvertently stray into a magnetic field of five or more Gauss. Although not as important as a pacemaker, mechanical watches and some digital watches will also be affected by magnetic fields. Magnetic fields of approximately 50 Gauss will erase credit cards and magnetic storage media.
The liquid nitrogen and liquid helium used in NMR spectrometers are at a temperature of 77.4 K and 4.2 K respectively. These liquids can cause frostbite, which is not a concern unless you are filling the magnet. If you are filling the magnet or if you are operating the spectrometer, suffocation is another concern you need to be aware of. If the magnet quenches, or suddenly stops being a superconductor, it will rapidly boil off all its cryogens, and the nitrogen and helium gasses in a confined space may cause suffocation. The only recommendation is to immediately evacuate the NMR room.
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Weizmann Institute of Science
Chemical Services, High Resolution NMR Facility