High Magnetic Fields
Large attractive forces are exerted on magnetic materials or equipment bought in close proximity to the NMR magnet systems which are always at field. The force may become large enough to move tools or equipment uncontrollably towards the magnet system and the closer to the magnet system the larger the force.
This is probably the main risk because it is one with which most people are unfamiliar. Risks come from release of any steel items/tools or equipment which are bought near the magnets. Even belt buckles, steel tipped shoes etc. may be strongly attracted to a magnet. This might result in damage to the magnets/probes (possibly resulting in a quench) or serious injury or death to personnel working near or under a magnet. The latter is probably the most serious risk, as staff and users often need to work under the magnet during its normal operation.
These risks are mimimised by preventing access to the NMR rooms by anyone other than the NMR staff and trained users. Anyone else needing to enter the NMR rooms can only do so in the presence of one of the NMR staff.
Warnings
Quench -- In the unlikely event of the magnet quenching or of a cryogenic failure, up to 100 m3 of helium and nitrogen gases may evolve over a period of several minutes. Although helium is inert, it is lighter than air and is non-toxic, there could be a risk of asphyxiation in a confined space. Personnel should evacuate the area in such a situation. A quench warranting evacuation would be obvious by the noise of the escaping gas and clouds of vapor.
Cryogens -- The cryogens used are liquid nitrogen and liquid helium. Boiling Point Temperatures: liquid nitrogen: -196° C and He: -269° C Color: none Toxicity: very low, Fire hazard: non combustible. Volume Expansion (from normal boiling point to room temp.): about 700 times. The main risks are of burns when handling cryogens and of asphyxiation if a magnet quenches. These are minimized by only allowing very experienced staff to fill the magnets with liquid nitrogen and liquid helium.Magnetic Field --The magnet of a spectrometer is always at field. Strong fields are produced outside the magnet; therefore, no movable metal objects should be allowed within 3 meters of the instrument. Small, sharp metal objects flying towards the magnet are highly dangerous. Larger objects (watch that floor polisher!) are troublesome to scrape off the magnet, and can seriously damage the magnet. Metal belt buckles, steel tipped shoes, and any other metal on the person may be strongly attracted when close to the magnet. Magnetic fields may permanently damage watches, calculators and certain types of credit cards. Keep those items more than 2.5 m away from center of magnet. Magnetic fields may permanently damage watches, calculators and certain types of credit cards. These items need to be kept well away from the magnets.
Magnetic fields may affect heart pacemakers. Demand-type pacemakers may be switched to basic rate pacing. Persons fitted with pacemakers should not come closer than 3 m of the center of the magnet. Medical implants e.g. clips, prostheses which may contain ferromagnetic materials would be subject to strong attractive forces near to the NMR magnet system. All people with such implants are excluded from the NMR rooms and appropriate warning signs are displayed. A recent publication suggests 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. The cumulative doses for an effect were large, and represent no hazard outside the 5 gauss safety line normally used. Reasonable caution in avoiding lengthy exposure to higher fields seems prudent, none the less. Our current conclusion then, is that NMR workers should then spend no longer than reasonably necessary within the 5 gauss line for sample changing and adjustments. No other equipment unrelated to the NMR system should be placed within the 5 gauss line. (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.) On Oct 31, 1996.
Magnets -- When installing a new NMR some factors must be considered. The weight of an instrument in the order of several tons and requires that it be placed in an area with substantial structural support. If the structural support includes steel beams or steel reinforced concrete, these ferromagnetic materials may have an effect on the magnetic field. The device should not be located near sources of RF such as heavy motors or relays. Personnel must be instructed on the hazards associated with an NMR unit. Recent publications 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. The cumulative doses for an effect were large, and represent no hazard outside the 5 gauss safety line normally used. Reasonable caution in avoiding lengthy exposure to higher fields seems prudent, none the less. Our current advice is that NMR staff and researchers should spend no longer than reasonably necessary within the 5 gauss line for sample changing and adjustments. No other equipment unrelated to the NMR system is placed within the 5 gauss line, which should be contained in the NMR rooms themselves. The NMR magnets will cause disturbance to VDUs etc in nearby laboratories on Levels 0 and 1 (e.g. where the stray field is 1-2 gauss). In many cases Users of nearby laboratories will need to screen their VDUs and advise etc. is available from the NMR staff. There should, however, be no safety implications. See: 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.
Video Display Terminals (VDTs) -- Extensive radiation measurements and health data do not indicate that these units present a health risk. Most of the symptoms related to the use of computer terminals are related to strain and discomfort that can be corrected by ergonomic measures. The potential for eyestrain can be reduced by the selection of terminals with non-glare screens, fitting a filter to the VDT, or improving the lighting conditions.
