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-----------------------------------------------------------To all,
I have kept silent so far on the subject of frost-free vs. not using
frost-free walk-in freezers, however, I feel compelled to relate an
experience that we had at our museum. We had been using a frost-free
walk-in freezer for several years for temporary storage of zoological
specimens, as well as for pest control, when the mechanism controlling
the warming cycle malfunctioned! The result was the freezer converted
itself to an oven. It happened over a weekend. By the time it was
discovered, many specimens were lost, and an odor of rotting flesh still
persists.
My recommendation is that whatever freezer is chosen, maintenance staff
should monitor its operation frequently- alarms may also fail!
[email protected] wrote:
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Hi all,
I will mention that the point on 'frost free' should not be applied so
heavily for the following reasons:
1)The defrost 'warming' cycles (the ones I measure don't allow any thawing)
are relatively short duration spaced out through the exposure time, and the
general response time of bagged materials commonly 'frozen' is
comparatively longer than the warming phase, often much longer, so only the
thinnest of objects would warm and chill in phase with the cycle. And these
we commonly bag and box up for physical protection or because we have a lot
of them to do at once.
2)Which is to say, the target insects will generally be kept cold though
the cycle by the cooling or cold object (thermal buffering) and will
experience the lowest temperatures the freezer can offer. They will have
been immobilized early in the cooling.
3)Household freezers are commonly 'frost free' so you will unnecessarily
restrict the pool of useful devices in your readership, many museums get by
fine with this form of device.
4)Frost free operation is designed to keep freezers running at optimal low
temperature without maintenance shutdowns (for chipping the ice off the
coils with a knife to void the warranty and find last summer's Popsicle you
saved for later).
5)The objects are bagged anyway so the warming cycle will not deposit
condensing vapour onto the object.
6)If you give credence to the need for 'multiple freezings', you get them
for free (for thin objects).
To test what I say, just put the naked bugs in a vial (the thinnest object
of all) in the freezer and follow the guideline you can derive from the
CF8(2) article I wrote. Frost free or not, the main point here is to ensure
efficacy and avoid harm to the objects.
While a manufacturer product selection guide is a pragmatic item, the guide
should emphasize the more timeless features which have proved useful in
practice so people can know the minimal features to get or trade off
against cost.
As a footnote, A.M. Read has the credit of starting it all with
refrigeration in the late 1800's, everyone else followed his lead.
see: L.O. Howard. 1896. Some temperture effects on household insects. Pp.
13-17 in Proc. 8th Ann. Meeting of the Association of Economic
Entomologists, USDA, Div. Entom. Bulletin 6-New Series, Govt. Printing
Office, Washington DC.
Tom Strang
Senior Conservation Scientist
Canadian Conservation Institute
Canadian Heritage/Patrimoine Canadien Heritage
Ottawa, Canada
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Everett D. (Tim) Cashatt, Ph.D.
Chair and Curator of Zoology
Illinois State Museum
Research and Collection Center
1011 E. Ash Street
Springfield, IL 62703
Tel. (217) 782-6689
FAX (217) 785-2857
http://www.museum.state.il.us/research/entomology/index.html
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