Compact storage of magnetic tape

Shane Bell <shane.bell [at] snark__slq__qld__gov__au> writes

>Recently the State Library under went a compactus refit. I am
>currently trying to source some information on the storage of
>magnetic tapes in a compactus system that involves the use of
>magnets as an alignment mechanism. In addition magnets may be in the
>compactus motors as well.

This subject has be discussed on other lists several time during the
last few years. I will attempt to summarize my understanding of the
issue:

In general it is prudent to keep magnetic materials such as audio
and video tape and data tapes away from magnetic fields or sources
of magnetic fields such as motors and magnets.  More specifically,
the source of the field would have to be very strong in order to
effect the tapes.  Also the tapes would have to very close, if not
touching the source for the field to effect the tapes.  Magnetic
fields are reduced by distance and the reduction is exponential. The
field falls off at the square of the distance.  So just a few inches
away from the source reduces the field significantly.

Small motors, of the type used to move mobile shelving produce very
low magnetic fields, which would be hard to even measure just of few
inches away.  One can attempt to measure it with a gauss meter.

Audio and video tape signals are hard to erase from the tape.  And
even harder with metal particle tape or video tape.  You can try it
with a test tape and see if you can erase or alter a tape by
exposing it to small motors and the like.

Having said this, we in the archival community  don't like to take
any chances, so as a precaution you may want to restrict any
magnetic materials on the bottom shelf of your mobile shelving
system.  (with at assumption the motors, wires and magnets are
located below the lowest shelf)  So the first foot or so could be
used to store other types of materials and the magnetic materials
would start from the second shelf on up.  Additionally, one could
install magnetic shielding material around any motors, magnets and
wiring. This would consist of a flexible metalized material that can
be found form an industrial or lab supply house.  It's probably not
necessary, but it would be inexpensive insurance and would bring you
and your donors peace of mind.

Here at Hollywood Vaults we have done some experiments with
recording test tones on quarter inch audio tape.  We then placed the
tape directly in contact with some high voltage electrical metal
conduit lines.  We examined the tones after six months and again
after six years and found no measurable difference.  Our tape
storage is a good twelve inches away form the conduits, so we feel
safe about the risk.  Pictures of our use of mobile shelving can be
found at <URL:http://www.hollywoodvaults.com>

You may be able to find additional information from one of the large
manufactures of mobile shelving, as they may have studies on the
subject that they can share with you since they sell their shelving
for just such a use. You might want to try
<URL:http://www.spacesaver.com>

David Wexler
Hollywood Vaults


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                  Conservation DistList Instance 14:17
                Distributed: Tuesday, September 12, 2000
                       Message Id: cdl-14-17-002
                                  ***