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7.5 Preservation of audio and video materials in tropical countries
Dietrich Schüller, Phonogrammarchiv, Vienna
Motto: Beware of high humidity and buy a hygrometer first!
Audiovisual data carriers play an ever-increasing role in the realms of information, communication, cultural documentation and research. With the vast spread of modern technologies, the wide field of the audiovisual domain has become an indispensable factor in every country around the world. In the course of this development, audiovisual collections have mushroomed almost everywhere, with each collection containing irreplaceable documents of unique historical and cultural content.
Beyond the world of modern, "international" entertainment, audiovisual documents are the only suitable records for otherwise undocumentable, orally transmitted cultures and arts. Thus, this kind of documents are an indispensable prerequisite for the representation of the world heritage in all its multicultural aspects.
It is now well known that audiovisual data carriers are prone to decay. Standards have been defined to help slow down the progress of this decay in order to prolong the life of this precious source material. The parameters of these standards have been defined within the prevailing environmental and economic framework of developed Western countries with moderate climatic conditions. Many of us have discovered, however, that, in tropical countries, audiovisual data carriers often have greatly reduced life expectancies. This paper will examine the reasons for this unfavourable situation and suggest measures to overcome at least some of the problems by observing simple, adaptable methods. The views of the author are based on the experience gained from a series of missions to African, Arabian and Caribbean audiovisual archives.
Before discussing the situation of tropical countries it is advantageous to generally survey the parameters relevant for the stability and integrity of audio and video carriers. Almost all audiovisual carriers (with the exception of the metal parts of mass produced audio or video discs) consist of polymers which are inherently unstable. All preservation measures can be defined as measures to retard decay as a consequence of this inherent instability and to prevent additional risks over what is defined to be "normal" conditions to their chemical, mechanical or - where applicable - magnetic integrity.
The generally accepted recommended storage and handling conditions can be summarized as follows:
1. The maintenance of low and stable temperature and humidity values.
2. The elimination of dust, fingerprints and other kinds of foreign matter.
3. The prevention of mechanical deformations.
4. The control of light and ultra violet radiation.
5. The control of magnetic fields (for magnetic carriers).
6. The use of well maintained replay equipment.
In principle, parameters 3 to 6 are as easy to achieve in tropical conditions as in temperate conditions. This is not the case, however, with temperature, humidity and dust. These parameters will, therefore, be examined more carefully in view of their influence on the stability of audio and video carriers
Temperature and Humidity
Before dealing with their influence on data carriers it must be explained that temperature and humidity are inter-related. The higher the temperature of the air, the more water it can hold in gaseous form (vapour); the colder the air, the less water it can hold. Put another way, the same, absolute amount of water at higher temperatures gives a lower Relative Humidity and at lower temperatures a higher Relative Humidity (RH). When the temperature is lowered, the Relative Humidity increases until the saturation point (100% RH) is reached. This point is also called the Dew Point because at that, and lower temperatures, water vapour condenses on to the surfaces within the environment. It is important to understand that the Dew Point is reached when, for example, air at 70% RH is cooled, without dehumidification, from 30EC to 24EC.
The speed of chemical processes is temperature dependent: the higher the temperature, the faster the chemical process. Aging is a chemical process and, therefore, the long-term stability of polymer carriers is, in principle, dependent upon the temperature of the environment in which they are kept: the lower the temperature, the longer the life expectancy; the higher the temperature, the shorter the life expectancy.
Water, omnipresent in the form of humidity or vapour, is - in the case of polymers - another agent working towards their degradation. Several decay processes are due to hydrolysis, a process whereby the long polymer molecular chains breakdown thereby altering their chemical and physical properties. Different polymers vary in their susceptibility to hydrolysis and the process is influenced by different factors in different polymers. However, the more water that is available (and the higher the temperature), the stronger its action and, again, the shorter the life expectancy. There is a trade-off between humidity and temperature: higher humidities can be compensated for by lower temperatures, and vice versa for the same hydrolytic effect.
The most prominent and widely discussed hydrolytic process affecting audio and video carriers is that which affects some types of magnetic layer binders used in some magnetic tapes. The binding properties are reduced and the tape becomes sticky and sheds oxide particles resulting in clogging of the replay head (colloquially known as the "Sticky Tape" or "Sticky Shed Syndrome"). This causes deterioration or even loss of the playback signal. To date, the only tapes affected have been some produced since the mid '70s. Normally such tapes can be stabilised to make them playable for a short period and, thus, provide sufficient time for the tapes to be copied. In severe cases the magnetic layer can be shed in flakes of varying size with consequent complete loss of information. Another process of polymer decay due to hydrolysis is the so-called "Vinegar Syndrome". It was discovered in the '80s and affects stocks of cellulose acetate films, causing them to become, initially, limp and, finally, brittle. The decay process produces acetic acid that acts as a catalyst and accelerates the process if trapped in the film can with the film. It has also become evident that the process can affect magnetic tapes with a cellulose acetate base, but not to the same degree as with film. These tapes also become brittle because of the action of humidity on the polymers. This leads to bad tape-to-head contact and, sometimes, irreparable tape breakages when being played.
Corrosion is another water-related chemical process. In theory, metal particle tape, as used for many video formats and for R-DAT, is prone to corrosion of the magnetic layer. It is noteworthy, however, that, so far, no significant reports of such corrosion have been received, not even from countries with a very adverse climate.
Beyond the sphere of chemistry, high levels of relative humidities can cause secondary problems. They support fungus growth, whereby fungus reacts with the surfaces of many audiovisual carriers, especially with the magnetic layer of tapes. In the replay process fungus accumulates on the replay heads of audio and video machines, causing head clogging and thus disturbing, if not hindering, the replay process. In severe cases fungus can destroy the magnetic layer. Another unwanted non-chemical humidity problem is condensation on the tape surface if the Relative Humidity reaches 100%. This can cause severe replay problems, especially with all rotary head formats (video and DAT). It can also lead to adhesion of the tape to the head-drum which may cause damage to the equipment.
Temperature and humidity also have an influence on the dimensions of carriers. Generally the volume of a carrier increases with higher, and decreases with lower temperature and/or humidity. With respect to thermal expansion, polyester tapes, wound on a spool, exhibit an anomaly. The polyester tape is pre-tensilized, which leads to different thermal expansion parameters for different dimensions. While the length of the tape is affected by temperature changes by a small amount only, the dimensional changes of the thickness exceed the changes of the length by a factor of about 10. Thus the tape pack of a polyester tape will become tighter with rising temperatures which can lead to excessive pressures and tape deformations, while cooling will make the tape pack loose. Acetate and PVC tapes react in the opposite way. (The author is indebted to Rudolf Müller and Friedrich K. Engel, both of BASF Magnetics, for their help with this point). Hygroscopic expansion of polyester is very low; for acetate cellulose, however, the expansion factor is quoted to be 8-15 times that of polyester.
Finally, higher temperatures result in a faster rate of increase of signal print-through on magnetic tapes. Print-through is only an annoying factor in analogue magnetic audio tape recording. Although, in principle, it has an influence on the longitudinal recorded sound track on analogue video formats, this is, in practice, only relevant for the older two- and one-inch-formats. It does not affect digital audio formats, nor any analogue or digital video signals. It only affects longitudinal sound tracks. It should be remembered that print-through can be greatly diminished by re-winding the tape several times.
From these facts the following general rule can be derived: for the extension of life expectancy, temperature and humidity should be low. With respect of the mechanical influences of these parameters, in order to prevent, especially with tapes, mechanical deformations caused by stress or undue relaxation, the chosen temperature and humidity level should be kept as stable as possible. Additionally, high levels of RH must be avoided in order to prevent fungus growth and mechanical replay problems.
It must be noted that there is no ideal storage condition per se. Each recommendation is a compromise between:
* The rate of decay of the carriers.
* The frequency of use of the carriers.
* The requirements for health and convenience of the archivists.
Current internationally accepted recommendations propose temperatures around 20EC with maximum (annual) fluctuations of ±2-3EC . The recommended humidities have been steadily lowered over the last few decades. As a consequence of magnetic layer binder break down with modern tapes since the mid seventies ("sticky tape" or "sticky shed syndrome"), humidity recommendations have dropped from a maximum of 60% to 40% RH and lower, with maximum fluctuations of ±5-10% RH.
These standard recommendations, which are quoted now for all audio and video carriers, are a typical compromise made from the perspectives of archives in moderate climatic conditions with the need of frequent access to their holdings ("access storage"). They reflect the general climatic conditions as well as a normal working room environment, which is generally accepted by people living in a temperate climatic zone.
More recently, long term "archival storage" - as opposed to "access storage" - conditions have been defined with lower and tighter parameters, suggesting 5EC and 30% or lower RH for magnetic tape (Van Bogart). Carriers stored under such conditions are, however, not easily accessible as they will have to be slowly acclimatised to a normal working environment before use. Current thinking does not encourage the storage of magnetic tape at temperatures lower than 5EC because of the risk of exudation of lubricants which are contained in the magnetic layer. These lubricants lead to head clogging with all its well known consequences. The Library of Congress in Washington is currently planning to systematically investigate tape storage at lower temperatures.
Turning now to tropical climatic zones, an outdoor temperature range of 25 to 40EC and more can be observed. Humidities may range from extremely (and for our carriers, favourable) low values in arid zones - but which then create dust problems - up to 100% RH in humid zones during the rainy seasons.
A considerable input of energy and money is necessary to bring down tropical temperatures and humidities and keep them at the values published in our standards. In practice, very few audiovisual archives in tropical areas can afford to keep to these recommendations. The most frequently applied practices are the following:
1. The archivists are unaware of the recommendations, or - for financial reasons - are unable to do anything. The audiovisual holdings are kept without any air conditioning at all.
2. The archivists are aware of the recommendations but have limited funds for air conditioning. They have cooling equipment running during the day, but they switch it off in the evenings and at weekends in order to save energy.
3. The archivists can afford cooling of the air but, because of lack of awareness and/or because of insufficient funds, do not effectively dehumidify their environment. Some of them may think that they are, at least, fulfilling 50% of the international recommendations by cooling down to perhaps 20EC but disregarding effective simultaneous dehumidification. In principle, cooling of the air simultaneously extracts water by condensation. Effective simultaneous cooling and dehumidification of an environment, however, requires specialised equipment and measures. Experience has often shown that standard air-conditioners, as used widely for cooling homes and offices - and also used in many small, Southern audiovisual archives - do not, in general, work effectively as dehumidifiers. A large part of this ineffectiveness can also be ascribed to improper insulation: any air intake that by-passes the controlled air conditioning channels will not only counteract cooling but also dehumidification.
In general, it can be stated that of these three mentioned practices the latter is the worst, and of catastrophic consequence if applied in humid areas like the Caribbean and similar regions. As explained above cooling without effective dehumidification raises relative humidities dramatically. Water condenses in corners without air current, on shelves, and, finally, inside audio and video cassettes. This leads very quickly to fungus growth, and to severe replay problems. There are indications that lead to the view that excessive levels of humidity may also trigger severe cases of hydrolysis. The Phonogrammarchiv has observed three such cases, all related to tapes that have travelled for long distances in the luggage compartment of an airplane before landing in hot and humid places. Obviously the cool tapes have received after their landing a high amount of condensing water which triggered hydrolysis. Other tapes of the same type that stayed at home have not, so far, exhibited this behaviour. As a consequence of these observations, we now advise researchers to carry both their blank and their recorded tapes in the cabins of airplanes only. Video archives employing this method of partial air conditioning reported that cassettes generally failed to play back after between one and three years only!
The other factor that creates a greater risk in tropical areas rather than in moderate climatic zones is dust. It is omnipresent in practically all southern countries. It is less annoying, where occurring, during the rainy seasons. Most aggravating is the fact that airiness is one of the principles of personal well-being in these countries. Hence, windows are normally left open. Modern office buildings sometimes do not even have windows in our sense but grids made of bricks to allow a constant air flow. Thus yellow or red dust covering floors, shelves, and inside everything, including tape boxes and even cassettes, is the standard scene in many archives and collections in these areas.
Dust is one of the greatest enemies of all audiovisual carriers and their equipment. On mechanical carriers, it deviates the stylus from its path, causing clicks and crackles; with magnetic tapes it causes head clogging, and, additionally, scratches on surfaces of tapes, tape heads and tape guides; with CDs it causes, in conjunction with improper handling, scratches which may render the discs unreadable. It must be remembered that CDs are sensitive to scratches. If their lower surface, the polycarbonate body, is scratched, the laser beam is dispersed and may not be able to track the pits. As a consequence, anything between short dropouts and total muting can occur. Scratching the protective varnish of the upper side of the disc will possibly render the reflective layer unstable, leading also to playback problems. CDs must, therefore, be handled with utmost care and should never be placed anywhere except in a player or in their cases, the so-called jewel boxes. Placing them on an obviously sandy table may lead to their swift destruction.
Recommended Practices for Tropical Countries.
Ideally, archives in tropical countries should follow the international recommendations for the storage of audio and video materials. For temperature, humidity, and cleanliness in an "access store" this would mean:
* A constant storage temperature around 20EC with fluctuations not exceeding ±1EC daily and ±2EC annually.
* A relative humidity of 30-40% with minimal fluctuations (±5%).
* The absence of dust particles.
Only rich archives are able to follow these recommendations. It must be noted, however, that such low temperatures are considered to be very uncomfortable by local archivists and may, moreover, constitute a considerable health problem. "Archival storage" in Van Bogart's sense would call for even lower and tighter values. In view of the costs that would be incurred, however, their realisation would not happen very frequently.
In order to reach, or to come close, to the above standards, a bundle of measures are necessary. The first and most important is the radical thermal insulation of buildings and rooms housing audiovisual storage areas. Whenever possible, storage areas should be placed in the centre of a building, their walls should not touch the outside of the house. Indigenous construction materials, eg like adobe, may be preferable to concrete and additional insulating material may be advantageous. Most important is the construction of secondary roofs and facades, with a gap of several feet between the primary and secondary surfaces, to allow for ample air flows around the primary building. This will prevent sunlight from hitting and directly heating the outside surfaces of the primary archival building. This is a simple and inexpensive but most effective measure. The use of underground storage areas may, in principle, help to reduce energy costs. The high risk of flooding must, however, be taken into account when considering such ideas. They are, therefore, only applicable (and still with great caution!) in dry areas. Generally, tropical rains can be abundant, so sufficient measures to prevent flooding of storage areas have to be provided.
In fighting against dust, the following measures must be considered:
Wrapping audiovisual carriers to individually protect them against dust, eg. in polyethylene bags, must, however, be critically examined for two reasons, especially in tropical areas:
1. Several deterioration processes are autocatalytic: the chemical process produces substances that act as catalysts for the further decay, thus exponentially accelerating the process. This is well-known with the Vinegar Syndrome that affects acetate cellulose and is also suspected with binder hydrolysis.
2. Equally, if not more important, is the danger of creating a microclimate: elevated humidities may be trapped, or accumulated, in closed environments, causing chemical decay and fungus growth with all its disastrous consequences.
The conflicting demands for airy storage and for dust prevention can only be met satisfactorily and simultaneously by providing a good air exchange, using appropriate air-conditioning equipment, in combination with the following radical dust proofing measures:
* Tightening windows to ensure a good seal.
* Installing air locks at all entrances.
* Having terrazzo-type floors. These are easily cleanable and, if dark coloured, make dirt visible and annoying.
* Air conditioners must be equipped with effective dust filters which must be regularly maintained.
What immediate advice could be given, however, if financial funds are lacking to provide ideal, "first world" conditions?
Thermal insulation and dust proofing can be provided at relatively low cost and have little or no continuing energy requirement. These should, therefore, be at the centre of all endeavours. As to temperature and humidity, it must be mandatory to control both parameters simultaneously. To this end, the availability of a hygrometer is an essential prerequisite. Air conditioning equipment must be chosen that is able to effectively cool and dehumidify the air. If compromises have to be made, temperature must be kept to a maximum of 25EC with the humidity not above 60% RH. If the level of both parameters cannot always be simultaneously achieved, it seems more important to keep humidity within the given limits than temperature. A stand-by generator must be provided to ensure a continuing power supply in case of a failure of the public supply. Whatever measures are to be taken, it is imperative that the temperature and RH values be recorded daily (or more frequently) in order to assess the risk and to take action.
It must be clearly understood, however, that such departures from the ideal climatic conditions will inevitably lead to shortened life expectancies for the carriers.
To improve the situation in the mid and longterm, the following strategies should be intensified:
* Development of cooperation on a national, or even regional, basis to establish central archival storage vaults with ideal storage conditions which can serve as repositories for several archives, libraries and other institutions. It is much cheaper to maintain one larger unit at a good climatic standard rather than several smaller units at a less than ideal standard.
* Development of international cooperation to establish large scale storage areas in cold climatic zones which can serve as longterm archives for the holdings of tropical countries.
* Intensifying, in cooperation with the manufacturers of audiovisual materials, research into measures to retard the decay of such products and to improve their longterm stability even under unfavourable conditions.
* Testing the potential of digital mass storage systems for assisting in the preservation of and access to audio and, hopefully, video documents in tropical countries.
While waiting for these strategies to bear fruit, however, the advice given above may help to improve the present situation. The current situation is often aggravated, as has been explained, by actions which are well-intended but in fact are counter-productive, eg the use of cooling without effective de-humidifying. It must be stated once more that the advice given above must not be seen as reduced standards that can be lived with. They are given as tools to overcome the present emergency situation caused by the interaction of two unfavourable factors in many countries:
* Disadvantageous climatic conditions -
- combined with -
* Tight economic conditions.
Under no circumstances must this advice be misunderstood. It must not be interpreted to mean that looser - and thereby cheaper - storage conditions would be sufficient to safeguard the audio and video heritage in the longterm.
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