Kodak D-31 manual Storage Vaults, Cabinets and Safes, Effects of High Temperatures

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 NFPA7 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.

4 D-31 June 2002