Brief: Cryotemperatures save flooded archives

In February 2010, "Xynthia", a major storm swept over La Rochelle, France. In order to rescue the archives of the "Conseil Général de Charente Maritime" the departmental authority that were covered with 2-metre deep sea water, cryogenic freeze-drying was used. The documents were first dipped in liquid nitrogen (-196°C) which killed all forms of bacteria and moulds. The small size of the ice crystals did not harm the structure of the paper fibres. The archives were then transported in dry ice to the central AAD Phenix centre in Bourges where they were again freeze-dried in dry ice (-78°C). This operation enables the sublimation (direct change from solid to gas state) of any water contained in the documents, which preserves the ink and makes the final restoration of the documents to an almost normal state. Furthermore, the operation was environmentally friendly and cost less than the estimated value of the archives themselves. Revue Générale du Froid et du Conditionnement d'Air, July-August 2010