Proper magnetic tape storage at the recommended temperature and relative humidity conditions is required in order to prevent audio tapes or video tapes from degrading prematurely.
The recommendations below are for polyester based magnetic tape. This generally refers to audio cassette tapes and video cassette tapes. It also includes audio reel-to-reel tapes after about 1970. Prior to 1970, many audio reel tapes had acetate as the base material. These tapes are much less stable and need to be digitized as soon as possible. If they cannot be digitized for a while, then storage under cool and dry conditions is recommended in order to slow the chemical degradation of the acetate base material.
The magnetic tape storage conditions for polyester base tape can be divided into two general categories according to the ISO standard:
The medium term storage conditions are for general short term storage of audio tapes or videotapes, the extended term magnetic tape storage conditions can be considered the archival storage conditions.
The maximum temperature for magnetic tape storage should not exceed 23 degrees C for prolonged periods of time. Short period peaks in temperature over 23 degrees C may occur, but these peaks should never exceed 32 degrees C. Tapes should not be stored lower than 8 degrees C because there is concern of problems occurring that are related to the lubricant in certain tapes. This is especially a concern for older tapes. In terms of relative humidity, the average magnetic polyester tape storage relative humidity should be in the 15 to 50 percent range. Cycling of temperature and relative humidity should be minimized as much as is feasible or possible. Generally, small fluctuations will not cause any issues, but large and sudden changes in storage conditions should be avoided.
Extended Term Storage Conditions
For these tape storage conditions, the ISO storage standard provides three temperature and relative humidity conditions to achieve the target of 50 years longevity. These three levels are:
Note that higher storage humidity is allowed if the temperature is lowered or higher storage temperature is allowed if the humidity is lowered. Any of the three conditions above will provide a minimum of 50 years life for the average tape. By choosing both lower temperature and lower humidity, a lifetime greater than 50 years can be obtained. For example, storage of tape at 11 degrees C and 20 percent relative humidity will provide greater that 50 years longevity.
As was the case for the medium term magnetic tape storage conditions, fluctuations in temperature and relative humidity should be minimized.
Note that when storing tape cold, special precautions should be taken to avoid condensation forming on the tapes. This means slow warm up times or ensuring the tapes are placed in sealed plastic bags prior to exposing them to a warmer environment. Usually tapes are placed in sealed type freezer bags prior to placing them in cold or cool storage.