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Re[2]: DeGaussing an MRI suite
Sorry my discussion offended you.
There's something I'm realizing about some radsafe subscribers; many
of you are very serious individuals. Frankly, I had never heard of
Static Magnetic, and was curious. It reminded me of the x-rays I
discussed below. If I offend you in the future, you'll just have to
get use to it. I don't intend to change at this point in my life, and
will find humor in any situation I can!
James H. Dunlap, Ph.D., CHP
______________________________ Reply Separator _________________________________
Subject: Re: DeGaussing an MRI suite
Author: radsafe@romulus.ehs.uiuc.edu at guardian
Date: 1/27/99 4:07 PM
I regret seeing something like this from an HP! This is the kind of
knee-jerk blow it off response I associate with some members of the IH
profession.
An MRI set generates a static magnetic field and the field away from the
unit can still be strong enough to magnetize ferrous alloy structural items
such as rebar and structural iron. This will cause VDT images to tilt. A
residual field of 2 mT is a substantial nuisance and also a pacemaker
hazard. The pacemaker issue has been discussed by ICNIRP in the journal
Health Physics so it is not a frat pledge gag either.
The fix is to hit the magnetized members with a strong 60 Hz field and
shake the magnetic domains back into randomness. This is what tape and disc
erasers do. But generating a field that can influence a structural member
some distance from the field source and maybe immersed in inches or even
feet of concrete or hidden behind walls or maybe something that has
asbestos in it (which means removing the barrier would be a no-no) is
another story and I don't know what sort of applicator would be used.
I recall the FAA had a problem with this in a building in New Jersey and
Noal May, MD, at their Oklahoma City facility may know who they called in
to degauss the building. I suspect he's at the FAA's Office of Aviation
Medicine, Civil Aeromedical Institute, Occupational Health (web site:
http://www.cami.jccbi.gov/AAM-700/index.html). An alternative is Aviva
Brecher, PhD: brecher@volpe.dot.gov who works with him. As mentioned in
another reply, ship degaussing is a major element in counter mine warfare.
The Navy has a Program Executive Office - Mine Warfare at 2531 Jefferson
Davis Highway, Arlington, VA 22242-5167, http://peomiw.navsea.navy.mil/.
Gordon Miller, CIH
miller22@llnl.gov
-----------------------------
> Are you pledging a fraternity? Periodically, a bunch of guys from one
> of the ivy league schools send a letter to Ann Landers describing some
> far-out, fabricated situation for her to reply to. She's pretty good,
> most of the time, about figuring out it was a joke. Your question
> reminded me of one I occasionally would get when teaching the
> 'uninitiated' lay person; viz., "What happens to the residual medical
> x-rays that aren't absorbed." My initial response was, "They bounce
> off of the patient, settle to the floor of the diagnostic radiology
> suite following patient exposure, and eventually are either swept up
> by the janitor or evaporate, but if you need to enter the room it's
> O.K.. because they'll just bounce off of you." Then I would tell them
> the truth. With regard to your question, I really don't have an
> answer, except to say I've never heard of residual "static magnetic".
> (Thats kind of catchy. Sort of like the internal dosimetry tables
> that Ken Skrable developed which have been referred to as the "Scrable
> Tables"). As an aside, but just a peculiar a phenomenon: I was once
> involved in a case with a hot cell where high-dose gamma sources were
> handled remotely, in which the thick glass window, after MANY years of
> exposure, 'shattered', due to being 'supersaturated' with electrons,
> but remained in the solid physical form. This apparently was because
> the glass was acting as a capacitor, and finally became
> 'supersaturated', and "exploded", similar to what happens when
> 'radiation trees' are produced when a piece of plastic is exposed to a
> very narrow beam of high energy electrons. So, maybe your question is
> valid. I too would be interested in an accurate discussion of this.
> Thanks.
>
> jim.dunlap@guardian.brooks.af.mil
>
>
>______________________________ Reply Separator
>_________________________________
>Subject: DeGaussing an MRI suite
>Author: radsafe@romulus.ehs.uiuc.edu at guardian
>Date: 1/26/99 5:09 PM
>
>
>Has anyone has any experience in dealing with the residual static magnetic
>fields that remain in an MRI suite after a unit is removed?
>
>The residual fields can reach 2 mT. This is too low to be a real health
>concern, but it's enough to cause problems for electronics and its enough to
>upset people.
>
>Degaussing is theoretically possible, but I can't find anyone who has
>actually
>done it.
>
>
>John Moulder (jmoulder@its.mcw.edu)
>
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information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html
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information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html