Safety Update

Static Magnetic Fields

November 20, 2008

Lori Stiegler
NSLS ESH Coordinator
stiegler@bnl.gov

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There has been much discussion lately at Brookhaven about static magnetic fields and what controls are necessary for work around magnets. We expect little change at the NSLS as the risks associated with our magnet use are low. However, you will see some new signs, and you might be contacted by the Occupational Medicine Clinic (OMC) or hear discussion, so I thought a review of this issue would be useful.

Static magnetic fields can pose potential hazards that include:

For low field, less than 0.5 millitesla (mT), 5 Gauss
Interference with the functioning of cardiac pacemakers, cochlear implants, insulin pumps, and similar devices; internal injuries from the movement of ferromagnetic implants (clips, pins and plates) and prostheses.

For high field, greater than 60 mT, 600 Gauss
Uncontrolled movement of ferromagnetic objects in high magnetic fields that cause injuries such as pinched fingers or being struck by metallic objects rapidly pulled toward the source; deletion of information on magnetic memory materials such as credit cards, identification badges, and computer disks (may occur in fields as low as 1 mT).

Because of these risks, the American Conference of Governmental Industrial Hygienists has set precautionary guidelines for workplace exposure, and BNL is required to comply with these limits. Workers with implanted ferromagnetic or electronic medical devices may not be exposed to static magnetic fields greater than 0.5 mT. Whole body exposure for all others may not exceed 60 mT for an 8-hour time-weighted average, or 2 T (20,000 Gauss) for a ceiling value. Exposure to limbs may not exceed 5 T (50,000 Gauss). Failure to comply with these limits could result in fines, and more importantly, injury to personnel.

At the NSLS, we have low fields (up to 10 mT) in the corridor from the Main Lobby to the Control Room on the west side of the building, which passes through an area that contains klystrons with permanent magnets. There are also small, locally posted areas at U7A, U4B, U4IR, and X21 with detector magnets, and by the Stock Room, where there is storage of a spare klystron. Ion pumps on beamlines have fields that drop below the 0.5 mT limit within a few inches. These areas could pose a hazard for people with medical implants. If you are not sure whether your medical implant is ferromagnetic, you should consult your physician. Those people with the above medical restrictions should enter the NSLS experiment floor via the VUV Ring doors, and stay clear of any of the locally posted magnetic field areas.

A few workers may need to work close to the high fields at detector magnets or klystrons. Special controls must be in place for working in high fields to avoid overexposure and injury. In general, keep your torso as far from the magnetic source as possible, and use non-ferromagnetic tools.

For workers that have "resident" status at the NSLS (both employees and non-employees), the OMC will send you a questionnaire, or you will be asked to fill it out when you go for your regularly scheduled physical in the next few months. This one-page questionnaire will allow the OMC physicians to evaluate any physical limitations and a record will be entered in your training database. If you have any questions about the OMC protocol, you can call the clinic at extension 3670.

Users who intend to bring magnetic field sources to the NSLS have to indicate that on their Safety Approval Forms so that the magnetic fields can be evaluated and the area can be properly posted for the protection of all our personnel.