NMR Facility - Safety Information

The main risks of working in the NMR laboratory come from the high magnetic fields, the handling of cryogens and high electrical voltages/RF sources. In general the risks can be minimized by limiting access to the NMR facility to only the NMR staff and authorized users of the instruments who have the requisite technical understanding and training.

High Magnetic Fields

An INVISIBLE magnetic field ALWAYS surrounds the NMR magnet in ALL DIRECTIONS. Large attractive forces are exerted on ferromagnetic materials brought in close proximity to the superconducting magnets. The force may become large enough to move objects uncontrollably towards the magnet - the closer to the magnet the larger the force. This in turn might result in damage to the magnets or probes (possibly resulting in a quench) or serious injury or death to personnel working near or under a magnet. This is probably the main risk because it is one with which most people are unfamiliar.

The risk is minimized by preventing access to the Facility by anyone other than authorized users. Anyone else needing to enter the NMR room can only do so in the presence of NMR Manager. Any maintenance work in the Facility must be supervised by the Manager and users are not allowed near the magnet during such work.

Static and oscillating magnetic field may affect medical electronic implants such as cardiac pacemakers. Medical implants e.g. clips, prostheses which may contain ferromagnetic materials would be subject to strong attractive forces which may result in serious injury. Therefore, all people with such devices are excluded from the NMR laboratory - appropriate warning signs are clearly displayed on the door.

Several studies suggested that long term cumulative large exposure to oscillating magnetic fields (60 Hz) may be associated with increased incidence of brain cancer in power industry workers. The cumulative doses for an effect were large, and represented no hazard outside the 5 Gauss safety line. In case of NMR or MRI laboratory major exposure results from static magnetic field. Currently, there is no data available related to health risks associated with long term exposure to strong static magnetic fields. Reasonable caution in avoiding lengthy exposure to high magnetic fields seems prudent, none the less. NMR staff and researchers should spend no longer than necessary within the 5 Gauss zone for sample changing, tuning, or other adjustments. No other equipment unrelated to NMR should be placed within the 5 Gauss line. In case of our Oxford (JEOL) magnet 5 Gauss line is about 1.5 m from the magnet axis. For Bruker this line is about 2.5 m from magnet center.

The stray field may erase information stored on magnetic tapes, disks, or other devices containing a magnetic strip (e.g. credit cards or security passes). Magnetic field may permanently  damage certain watches and calculators. These items need to be kept well away from the magnets.

Cryogens

The cryogens used in the Facility are liquid nitrogen and liquid helium.

Temperature: nitrogen: -196 and helium: -269 o C
Color: none
Toxicity: none
Fire hazard: non combustible
Volume expansion (from normal boiling point to room temperature): ca. 700x

The risk of burns while handling extremely cold cryogens is minimized by only allowing experienced personnel to carry out cryogens' fills.

Another risk is associated with possible asphyxiation in the event of magnet quench. During the quench helium and nitrogen suddenly evaporate and expand their volume leaving no air in the room. This is extremely dangerous condition since exposure to atmospheres containing 8-10% or less oxygen will bring about unconsciousness without warning and so quickly that the individuals cannot help or protect themselves. Therefore, it is imperative that in the event of quench (which is quite obvious because of the noise of escaping gases and clouds of vapor) all personnel should instantly evacuate the area. The room will be safe after few minutes. A more detailed discussion of risks associated with superconducting magnet quench can be found on the SIUC NMR Facility website .

The magnet cryostats continuously expel a small quantity of gaseous He and N2 into the air. This does not present a hazard since during everyday use the air is constantly changed in the NMR Facility by the air-conditioning system.

Electrical/RF

Risks are similar to those encountered in the use/maintenance of other electrical laboratory equipment and are minimized by restricting any modification/maintenance of the equipment to the trained personnel in consultation with the system manufacturers.