[PADG:563] Re: Cold Storage

["Loren C. Pigniolo" <misterpuerh@xxxxxxxxxxxxx>]

It is correct that RH does not really matter if the temperature is below freezing.  Most of the water will be solid with very little chemical action taking place because of the temperature.  At any rate, there is no practical way to accurately measure RH at such low temperature.  As materials drop below freezing, the effective RH drops by about 12-15 percent.  However materials can pick up or loose water content in a freezer, though it happens slowly.  If materials have gained water, when you bring the material back up to room temperature you may have a humidity problem.  If by chance they have lost water by freeze-drying ("freezer burn") or they were too dry before entering the freezer then you may have problems with embrittlement.  Your engineers should be able to ensure against water loss, but water gain will probably be more difficult to control due to defrost cycles, even with your low RH.  Mark McCormick-Goodhart's moisture indicator method was devised to minimize water gain and to warn when materials would be threatened when brought back to room temperature.  A different buffering/warning system is used with their cabinet method (see their website http://www.wilhelm-research.com).

You have several things to consider:

What type of material will you store at low temperature?  Photographic film (cellulosic), for example, has a good deal of water content and will need to be packed so that the space around the material is less than 1 cm.  This prevents the formation of frost inside the box, package, etc, when the material drops in temperature and when it is brought back to ambient temperature.  Paper materials should be much less of a worry, but theoretically the same thing can happen.

Your basic problem is how to minimize frost in such a vault and to keep materials inside protected from it.  Defrost systems warm the air inside the freezer a few degrees so the frost melts.  This has a cycling effect on temp, but it can be minimized and still remain effective.  You already have an advantage with the low water content of your air.  However, the more you open the freezer, the more frost you will build up.  As mentioned above, for photographs, Henry Wilhelm and Mark McCormick-Goodhart have devised either individual plastic packaging (for small collections) or cabinets for use with larger collections.

You will also need to devise a method to warm whatever size of materials you are planning to remove from storage.  Depending on the bulk of the material, this might take several hours or a day to warm.  The slower you warm, the better, though you can calculate dew-point to determine how fast the materials can warm and what a safe temperature would be before removing from a secondary container.  Remember to calculate based on the temperature at the center of a group of materials.

Also, the more you remove the materials, the less effective it will be to have the materials stored at low temperature.  An earlier response mentioned the damage from removing materials even a few days a year.  The materials are not so much damaged physically - tests have shown freeze-thaw cycles to have a negligible impact on most archival materials (paper, photographs) - as the benefit of freezing is rapidly lost due to time out of storage.  Just a little of this on a regular basis can turn an expected 2,000 years into 50 or 100 years.  There are calculators available to see the estimated effect of this.  The bottom line is, if you are going to benefit by keeping your materials below freezing, you don't want to remove them on a regular basis.  For materials you need to access more frequently, a cool or cold environment would be more practical and cost-effective.

In addition, you will definitely want to install climate monitoring equipment so you can track the performance of your freezer.  You also need to have alarm points to alert staff to a problem or failure even when everyone is off on vacation.

The National Archives of Canada has done extensive testing on cold storage.  They maintain perhaps the most extensive variety of climate zones in the world at their Gatineau facility.  Email me directly if you would like a contact there.

Loren C. Pigniolo
Preventive Conservation Specialist
San Francisco, CA
925.788.2231 (cell)

-----Original Message-----
From: Chris McAfee <McAfeeCK@xxxxxxxxxxxxx>
Sent: Jul 13, 2005 7:40 AM
To: padg@xxxxxxx, consdist@xxxxxxxxxxxxxxxxxx
Subject: [PADG:559] Cold Storage

Please excuse the cross-posting.
 
As some of you know, the Church of Jesus Christ of Latter Day Saints is
building a new archives/library/preservation building. We want to build our
"vaults" to the highest standard possible. We are currently working under the
idea that we will have an area with -4 degree F cold storage for our most
valuable items (see http://www.wilhelm-research.com/). However, our building
engineers are concerned with problems of maintaining proper humidity levels,
keeping frost out, etc.
 
As we've consulted with other archives who have cold storage, their building
engineers have expressed concern with our desire to have -4 degree storage and
this has "frightened" our own building engineers. Of course, none of these
individuals have any cold storage less than 25 degrees and they have not dealt
with anything colder. So I have 3 requests:
 
First: I want to know (from a conservator's or preservation administrator's
point of view) how the physical rules change once you drop below 0 degrees.
 
Second: As most of the facilities we've talked to are also in more humid areas,
I also want to know how the physical rules change in a dry climate like Utah.
 
Third: If those of you who deal with cold storage (35 degrees F and lower) on a
regular basis, could make general comments on problems and solutions you've
experienced, it would be greatly appreciated.
 
Thank you,
Christopher McAfee
 
Christopher McAfee
Senior Conservator
Family and Church History Department
The Church of Jesus Christ of Latter-day Saints
50 E. North Temple St. Rm. 227E
Salt Lake City, UT 84150-3420

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