We recently visited a record office to help set up a wireless temperature and humidity logging system in their archives. They had been experiencing problems with mould growth on the records, some of which could be over a thousand years old. To reduce the levels of damage to the records, they wanted to be able to closely control temperature and humidity levels.
Archives in general
Archives are an accumulation of historical documents collected over the life-time of an organisation.
National archives collect, catalog, and secure historical & present day materials from their country. Besides preserving & organising collections, archivists face the great challenge of deciding which records are assigned a lasting value for research purposes and could contribute to the understanding of the country’s history.
Furthermore, archivists transfer the information to more resistant media by digitising documents, drawings, and photographs. This makes it easy for researchers to access conserved items without the risk of damaging the originals.
Ancient Etruscan script
In spite of all the new media available these days some legacy materials need to be preserved in order to show their uniqueness. The oldest preserved book in the world is possibly an Etruscan script discovered in Bulgaria. It is estimated to be more than 2,600 years old.
Besides all the academic work necessary it requires great technical effort to create the best possible storage conditions suitable for the form of the objects to be preserved. For example; papyrus and paper require different temperature and humidity conditions compared with microfilm tapes.
Environmental factors in archive stores
– Radiation in the form of light will cause paper to yellow and ink to fade considerably.
– Air pollutants such as dust and chemicals accelerate the degradation of important documents.
– Vibration for example of archive stores caused by vehicular traffic or construction work can cause mechanical stress on collections.
– Insect pests can lead to severe damage through bites and deposits.
– Temperature & humidity are the most significant factors that have an impact on archive collections and often interrelate with other environmental factors.
Why the need to measure relative humidity?
As in museums, incorrect temperature and humidity levels cause damage to documents, books, photographs and drawings. The rate of decay can double with an increase of as little as 5 °C. Generally warm & damp conditions provide more energy and so increase the speed of decay.
High temperatures can cause document wax seals to soften and even result in the combustion of cellulose nitrate film. At low temperatures organic and plastic materials become brittle making them prone to physical damage. However, one of the most significant consequences of incorrect temperature is the incorrect relative humidity that can result – temperature has a direct effect on relative humidity and vice versa.
This particular fact of course is the same in museums, but is often much harder to control in archives since proper ventilation is not easy to achieve in between multiple shelves fully loaded with collections. Studies have shown large deviations of temperature and therefore also humidity (RH) within an archive section. In general, it is recommended to keep the temperature between 20 – 22 °C and humidity be-tween 50 – 60 %rh in archives where organic material is stored. Otherwise a temperature drop can make condensation inevitable.
A damaged book.
RH above 65 % encourages mould and pest activity, RH below 45 % leads to desiccation, shrinking and cracking of organic materials.
The main challenge for architects, and heating, ventilation and air conditioning engineers is to create the most homogeneous controlled storage environment possible.
Philip Robinson Rotronic UK