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Re: TLV's for Static Magneti
Reply to: RE>TLV's for Static Magnetic Fields
In TLV terminology, a "ceiling" is a not-to-exceed number, regardless of
duration. So one could go to 20,000 gauss so long as the day's average
exposure was 600 gauss. By that guidance, one must keep static magnetic field
exposures below 4800 gaussohrs. So one could be exposed to 20,000 gauss for
0.24 hrs. if there were no other static magnetic field exposures on that day
(the earth's field is about 1/2 gauss so 4 gaussohours won't make a big
difference). The rationale for it is my paper in the Dec. 1987 issue of the
AIHA Journal (48: 957-968, Dec. 1987).
There is another, more recent, guideline from ICNIRP (H. Phys. 66: 100-106,
Jan. 1994). The 8 hr. TWA there is 2,000 guass. The ceiling there is also
20,000 gauss. It allows extremity exposures upto 50,000 gauss without
specifying exposure time.
The research underpinning the current TLV was done in the mid-80s; ICNIRP had
the benefit of more recent research which allowed them to differentiate between
medical electronic implants and passive implants such as pins, clips, etc.
They advise the place to become concerned about metallic objects, including
tools, is where the field exceeds 30 gauss. LLNL guidance is to look for
places where forces on tools, etc. can become a problem by using the crude
device of fastening a string around a ferrous alloy washer, fasten the other
end around a belt loop, and dangle the washer, in places where magnetic fields
exceed 30 gauss. Magnetic force is a concern where the washer is pulled
towards a magnet. ICNIRP sticks with 5 gauss as the warning criterion for
pacemakers.
The 600 gauss limit first appeared in an LLNL management publication,
Supplement 26.12 of it's Health & Safety Manual, back in 1986. That supplement
was recently revised and adopted the ICNIRP guidance and I wrote a letter to
the Physical Agents TLV Committee Chair, laser guru Dave Sliney, advising him
of the ICNIRP guidance and recommending that ACGIH adopt it. Those of you on
the web can see this material, as well as all other LLNL ES&H-related managment
publications by accessing the LLNL home page. I can send a copy of this
particular supplement tp those who request it (please stay off Radsafe and use
the address in this message instead).
--------------------------------------
Date: 1/29/96 5:17 AM
To: GORDON MILLER
From: radsafe@romulus.ehs.uiuc.edu
Is this the correct interpretation of the ACGIH Threshold Limit Values
for Static Magnetic Fields? (I have a 1994 edition of the TWA booklet
that listed this information as "Proposed Changes".)
------------------------------------------------------------------------
Persons who wear pacemakers or other medical devices
(Includes medical implants such as sutures, clamps, etc) = 5 Gauss (G)
Ceiling value for workers (ceiling value)* = 20,000 G
Time Weighted Average Whole Body Extremities
8-Hour TWA 600 G 6,000 G 4-Hour TWA
1,200 G 12,000 G 2-Hour TWA
2,400 G 20,000 G* 1-Hour TWA 4,800 G
20,000 G* 15-Minute TWA 19,200 G 20,000 G*
We are evaluating the construction of a building which will be used by
researchers who will be using superconducting magnets. We want to be
sure that adequate warning is provided to pacemaker/implant wearers that
magnetic fields are being produced.
************************* /^\ /^\ *****************************
Tad Blanchard /___\ /___\ NASA-Goddard Space Flt Ctr
Nat'l Health Svc, Inc O Greenbelt, Maryland
Sr Health Physics Tech / \ Phone: 301-286-9157
/___\
Tad_Blanchard@ccmail.GSFC.NASA.gov
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Subject: TLV's for Static Magnetic Fields
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