machine can cause cell destruction as well as genetic damage. The user must always be alert to the on/off status of the X-ray beam, keep aware of the location of the beam, and know how to work safely around the beam when aligning it in preparation for conducting an experiment. Machine warning lights indicate when the beam shutter is open. Users are required to wear a monitoring badge to measure any accumulated exposure.

7.C.8.4 Miscellaneous Physical Hazards Presented by Electrically Powered Equipment

7.C.8.4.1 Magnetic Fields

An object that moves into the attractive field of a strong magnet system, such as a nuclear magnetic resonance (NMR) system or any other instrument system requiring a superconducting magnet, can become a projectile that is pulled rapidly toward the magnet. For example, the large attractive force of an NMR requires that objects ranging from keys, scissors, knives, wrenches, other tools, oxygen cylinders, buffing machines, and wheelchairs, and other ferromagnetic objects are excluded from the immediate vicinity of the magnet to protect safety and data quality.

Magnetic fields of ~10 G can adversely affect credit cards, watches, and other magnetic objects (see Table 7.1). Computer and television screens in neighboring areas may be affected by shifts in small, peripheral magnetic fields as magnets are brought up to field or decommissioned. Prudent practices require posting warnings, cordoning off the area at the 5-G line, and limiting access to areas with more than 10 to 20 G to knowledgeable staff. Keep people wearing heart pacemakers and other electronic or electromagnetic prosthetic devices or other potentially magnetic surgical implants, such as aneurysm clips, away from strong magnetic sources. Repairs done in the vicinity of a strong magnet should be performed with nonferromagnetic tools.

TABLE 7.1 Summary of Magnetic Field Effects


Effect

Field Strength at Which Effects Occur (G)


Effects on sensitive equipment such as electron microscopes, image intensifiers, and nuclear cameras

1

Disturbance of cathode ray tubes; possible detrimental effects on medical equipment, such as pacemakers, implants, surgical clips, or neurostimulators

5

Erasure of credit card and bank cards; disruption of small mechanical devices, such as analog watches and clocks; and disturbance of X-ray tubes

10

Destruction or corruption of magnetic storage material

20

Saturation of transformers and amplifiers

50


SOURCE: Adapted from Site Planning Guide for Superconducting NMR Systems (Bruker BioSpin GmbH, 2008b) and General Safety Considerations for the Installation and Operation of Superconducting Magnet Systems (Bruker BioSpin GmbH, 2008a).

Magnetic fields operate in three dimensions, and when considering the impact of an instrument, field strength should be checked on the floors above and below the floor where a superconducting magnet is installed. The 5-G line should be identified in all affected rooms, and appropriate warnings should be posted.

Because superconducting magnets use liquid nitrogen and liquid helium coolants, the precautions associated with the use of cryogenic liquids must be observed as well. (Also see section 7.E.2.) If the superconducting magnet loses superconductivity because of damage, physical shock, or for any other reason, the coil will heat the cryogenic liquid that surrounds it, the magnet will quench (lose field), and the helium will boil off rapidly into the surrounding space. Low-oxygen alarms are recommended in rooms where instruments with superconducting magnets are located. In the event of a quench, all personnel should leave the area and not return until oxygen levels return to normal. If emergency personnel must enter the area before the oxygen levels have been verified, they should wear a self-contained breathing apparatus (SCBA).

Rooms containing superconducting magnets should provide enough clearance for coolant fills to be performed safely.

If an object becomes stuck to a superconducting magnet, do not attempt to remove it, but call the vendor of the magnet for guidance. Attempting to remove the object could result in injury to personnel and damage to the magnet. It may also cause the magnet to quench, releasing dangerous quantities of gaseous helium into the area.

7.C.8.4.2 Rotating Equipment and Moving Parts

Injuries can result from bodily contact with rotating or moving objects, including mechanical equipment, parts, and devices. The risk of injury can be reduced through improved engineering, good housekeeping, and safe work practice and personal behavior. Trained laboratory personnel must know how to safely shut down equipment in the event of an emergency; must enclose or shield hazardous parts, such as belts, chains, gears, and pulleys, with appropriate guards; and must not wear loose-fitting clothing, jewelry, or unrestrained long hair around machinery with moving parts.



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