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[filmscanners] Re: What can you advise?
Thank you for further clarifying this matter and your detailed
commentary about relative humidity. I knew there was an issue there (my
dehumidifier instructions went on about it, at some length), but I
wasn't clear on the exact methods of measurement.
Our film storage area is only heated during the winter to about 60
degrees F, which means it can fluctuate to below that at times. Living
in a "temperate" rain forest, most winters we get rain about 20 or more
days a month here, and the humidity level indoors is ridiculously high
(if not reduced via dehumidification even our double pane windows sweat
rivulets). This house seems to only let moisture IN... ;-) We also do
a lot of cooking and canning in the fall/winter months. We also have a
lot of house plants, which we've been slowly reducing because of the
moisture problems. We've removed several larger trees that were on the
house or very near it, as they reduced circulation and added and held
moisture. It was sad to have to see them go, but the roof was rotting
and had to be replaced because of them. Living in a rain forest is not
without consequences ;-).
Running the dehumidifier for a 24 hour period during the winter months
can lead to as much as 1-2 gallons of water removed from the air here.
Although I have not encountered mold growth on any films (knock wood)
before we bought the dehumidifier we did have mold problems in several
rooms, especially those that were not used often, in corners between
wall and ceiling or wall and wall.
Bob Frost wrote:
> As a former mycologist, I too was rather suprised when you said molds could
> grow at anything over 30% humidity. I once studied the effect of humidity on
> the growth of a mold for my PhD, and found that unless the mold was growing
> on a substrate containing plenty of water, it couldn't grow out into air of
> less than 95% humidity at normal room temperature.
> The problem is that last word - temperature. As an example, 80% relative
> humidity at 25 degrees C is equal to 30% at 5 degrees C, so a mold that
> needed 80% humidity at 25 degrees would be able to grow at anything above
> 30% humidity at 5 degrees. This is because the measurement of humidity that
> is normally used, relative humidity, is fine for comparing humidities at
> constant temp, but when you change the temp, the water-holding capacity of
> the air changes dramatically, and other measures such as 'saturation
> deficit' are needed to properly compare the ability of the air plus moisture
> to support growth at different temperatures.
> Plus of course, the biggest danger is condensation. If the temperature drops
> below the ability of the air to hold the moisture, the excess will condense
> out (dew at night, fogging of lenses when you bring a cold camera or pair of
> spectacles into a warm room). A cold outside wall to a room may suffer
> condensation and mold growth for the same reason, even though the general
> humidity of the room would not support growth.
> Bob Frost.
> ----- Original Message -----
> From: "Arthur Entlich" <firstname.lastname@example.org>
> To: <email@example.com>
> Sent: Monday, September 30, 2002 12:28 AM
> Subject: [filmscanners] Re: What can you advise?
> As both you and Henning suggested, based upon review of my files, my
> suggestion of mold growth at over 30% humidity was too conservative.
> After doing a scan of my physical paper files, I found my memory had
> failed me, as a reference by Kodak regarding preventing fungal growth on
> films indicated humidity levels should be kept under 50%, not 30%, as I
> had indicated. (Kodak Pamphlet AE-22) Prevention and Removal of Fungus
> on Prints and Films
> I then did a Google search, and several sources suggested anything under
> 60% was probably safe.
> So, it would appear your 45% humidity level is safe under most
> Kodak and other sources did suggest fungicidal agents can be used during
> the processing to further lessen risks.
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