RE: [AV Media Matters] metal vrs wooden shelving for VHS tape sto

[rwarren@pantheon.yale.edu]

Hi Folks,

There have been many interesting and valid comments about metal
shelving, which for many reasons such as cost and availability, all
of us are probably doomed or blessed to have to accept most of the
time. Experience here has suggested that its drawbacks include the
facts that the normal finishes applied are usually maddeningly
slippery and that units supplied with vertical dividers are menaces
in studios because they vibrate.

The comments about wooden shelving being out of place in archives,
however, reminds me of an incident related by a colleage in the
sound archives profession (sorry, this was years ago and
documentation unavailable): There was a fire in one room a
multi-room tape-storage area which included both metal and wooden
shelving. Tapes and papers in the room with the fire were damaged or
destroyed. Most of the tapes stored in the adjacent room with metal
shelving (either next to or above the fire) were ruined by
conduction of heat through the metal of the shelves (and, as I
recall, further damaged by buckling and collapse of shelves),
whereas most of those in the adjacent room with wooden shelves were
not damaged because of the lack of heat conduction by the wood and
its retention of structural integrity.

Yes, wood has its problems, and, if used, must be finished so as to
seal all sides to prevent escape of as much as possible of all its
types of gases (sorry, I'm not good at proper chemical terminology).

For these reasons, among others, it may not be sensible totally to
reject the idea of either wood or metal shelving.

(Potshots and flaming cheerfully accepted, but outside the storage
areas -- plastic or concrete shelving anyone ? How about
polycarbonate ?)

-Richard Warren (sometimes known as the inventor of sticky-tape
syndrome and thus already terminal), Historical Sound Recordings,
Yale Music Library

At 08:16 AM 04/05/00 -0700, you wrote:
>Many years ago I was involved in magnetometer measurements of a potential tape
>library room and associated commercial standard sheet metal shelves.
>
>We found even after banging around the shelves to assemble them into the snap
>in brackets holding the shelves that the field was still of the same magnitude
>as the earth's natural field, 400 mGauss, measured inside a steel framed concrete tilt walled building.
>
>The metal studs inside sheetrock walls were found to have slightly enhanced
>magnetization at the points where power driven screws held the sheet rock to
>the metal stud.  Therefore, we chose to "shield" the walls that were outside
>walls to hallways with the shelving placed flat to the wall.  This also gave
>an extra measure against outside randome influences, such as motors on floor
>buffers, etc.  This storeage area served as the active 7 and 9 track digital
>tape library for many years, with no problems from metal shelves.
>
>It is true that a sharp blow to metal will induce at least the magnetization
>of the earth's field, but this is well below the hazard level to today's high
>coercivity tapes.
>
>I agree that wood shelves have no place in an archive, since that is a
>combustible material.  Issues of humidity absorption also could be an issue
>with wood, and that is a greater danger than the fire risk, as humidity is
>something we constantly fight to preserve older recordings on plastic media
>with binders that hydrolyze.
>
>It is good to be aware of materials for a proposed archive, and
>magnetometer probes can be obtained to work with various electronic
>DC current meters. Thus, an archive that is growing could have its
>instrumentation to actually measure proposed materials, and document
>incident fields in storage areas. One area I surveyed had a motor
>generator room on the other side of the sheetrock wall.  For that
>case, I added metal sheathing over the wall, with overlapped seams
>to add a measure of shielding, and placed two by four lumber bolted
>flat to the wall to add the protection of spacing.  The metal
>shelves were bolted to the spacers.  Using the formula for field
>decline, I believe we showed two inch spacing nullified the effect
>of a strong magnetron test magnet held flat against the other side
>of the wall.  Such a magnet had been demonstrated to be strong
>enough to erase digital tapes in use at the time. If anyone needs
>precise figures, I could reply privately, after digging out the
>archived documents.
>
>However, there are companies that provide even better shielding materials
>than
>the sheet mild steel I had available.  It has been years since I dealt with
>them, but we also purchased mu metal products from Perfection Mica Corp. in
>the U.S. Midwest.  They produced sheets and mu metal tape carriers that
have
>been used in our field transport of research masters to the lab from all
>over
>the world with great success in protecting the master tapes from magnetic
>environmental effects.
>
>Stuart M. Rohre
>University of Texas Applied Research Labs, ESL
>Analog/Digital Tape Facility