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4 D-31 June 2002
Storage Vaults
The highest degree of protection for a large
number of records is afforded by a fireproof
storage vault or record room. It should be located
and constructed in accordance with the local
building code, Fire Underwriters’ Regulations, and
the requirements of the National Fire Protection
Association (NFPA)
7
for a valuable record
room, except that an approved, controlled,
air-conditioning unit should be installed. While
NFPA discourages air conditioning such an
installation, the fire hazard introduced by
openings for air-conditioning ducts can be
overcome by the use of automatic, fire-control
dampers approved by Underwriters’ Laboratories,
Inc. These can be installed in the ducts in
accordance with recommendations of NFPA.
8
Sufficient insulation should be provided in the
vault to permit satisfactory temperature control at
all seasons of the year and to prevent moisture
condensation from forming on the walls.
Cabinets and Safes
For smaller quantities of records, a fire-resistant
cabinet or safe of the type described by NFPA
7
will provide considerable protection. Such a safe
should protect records against a severe fire for at
least four hours.
Many fire-resistant safes and cabinets use a type
of insulation that when heated releases moisture
and thus fills the interior of the safe with steam
during a fire. This can cause melting or stripping
of the film emulsion layer and loss of the image.
For protection, films stored in such a safe should
be placed in moisture-tight cans, as described
under “Humidity Control” in this publication.
It is preferable to use fire-resistant safes that are
available with an inner chamber sealed against
moisture. These are classified by Underwriters’
Laboratories, Inc., as Class 150 Record
Containers.
9
Film damage caused by steam
is not a problem with these safes.
The question is sometimes raised as to whether
microfilm stored in drawers or cabinets designed
to resist fire for several hours might, in case of a
fire, generate enough pressure to damage or
explode the cabinet. There is practically no
danger of an explosion from the storage of either
Estar Base or acetate base safety film under
these conditions. There are small amounts of
organic materials in acetate film base, as well as
moisture, which will expand under heat and, under
some conditions, might generate slight pressure.
However, such intense heat would be required on
the outside of the fire-resistant cabinet that the
cabinet would be seriously damaged from the fire
before appreciable pressure developed.
Effects of High Temperatures
In addition to complete loss by fire, damage to film
records can also occur if they are exposed to very
high temperatures. Excessive heat causes film to
buckle because of shrinkage at the edges. When
severe, this distortion affects the ease with which
the information can be taken from microfilms,
either by projection (for reading) or by printing
onto another film.
Silver-gelatin films that have been conditioned at
a relative humidity of 50% or lower will withstand
121°C (250°F) for 24 hours without significant
loss in readability or printability. At 149°C (300°F),
severe distortion can occur in a few hours.
Films that have been conditioned at a relative
humidity above 50% may show objectionable
distortion in somewhat shorter times or at lower
temperatures. Higher humidities, however, are
undesirable for other reasons, as explained later.
Thermally processed silver films will build
up background densities fairly rapidly at
temperatures of 93°C (200°F) and above.
At these temperatures, even a few hours will
produce significant loss in readability or
printability. At 149°C (300°F) or above, severe
distortion can occur in a few hours.
Diazo films, while quite stable, contain dye images
that can fade and/or discolor as a result of high
temperatures. Kodak Diazo Microfilms can
withstand a week at 93°C (200°F) without image
loss. At 149°C (300°F) or above, severe distortion
can occur in a few hours.
High temperature is the greatest enemy of
vesicular film. Although Kodak Thermal Print
Films can withstand 71°C (160°F) for several
hours, high temperatures can cause a complete
loss of images if care is not taken with regard to
temperature control.