I think this might be of interest to many of you. Perhaps this "explosion"
is a rumor known to some of you and needs to be dispelled. In any case, it
is useful info and will probably provide a chuckle or two.
We have a ~15 year old Spectrospin/Oxford 270 MHz magnet which developed a
leak around the O-ring seal of the base plate. We have been pumping on it
~3 days/week to keep it alive for the last 3 years. A couple of weeks ago
we were told by a reputable person that the magnet in this situation could
develop a pressure build-up and explode. I was told it could be a "bomb"
containing oxygen condensed from the air into the "vacuum". I was also
told that there were two known occasions in which such a situation resulted
in an explosion of the magnet. One imbedded shrapnel in the wall and the
other resulted in a minor injury. This info supposedly came from Oxford.
So - we quickly and cautiously de-energized the magnet and began to warm
it up. Some of our observations made me decide to talk to Oxford myself,
which is what I should have done initially. I learned that: there have
been no such events as described above. Rather: One magnet did quench
violently and was destroyed. That happened because it was not properly
maintained. It developed an ice block in the nitrogen fill stack and in
the helium fill stack. The pressure build-up in the nitrogen dewar caused
it to rupture and that ruptured the helium dewar. In the situation we (and
others of you) have, Oxford says there is no such danger. However, Oxford
does have a safety bolt replacement kit available for older systems without
a safety relief valve.
Dr. Joseph Vaughn, Manager NMR Facility
Chemistry Department
Florida State University
Tallahassee, FL 32306
Phone 904-644-3334
-9636
Fax 904-644-8281