Understanding storage environmental stability during power outages: A key issue in sub-tropical climates

Efficient air-conditioning systems facilitate climate control in modern museums, libraries, and archives. The climate in Hong Kong is typically hot and humid, so the survival of collections is highly dependent on 24-hour air-conditioning systems to maintain the desired environment in repositories of archives and books, or artefact stores. The continuous operation of such systems in turn relies on a number of factors, such as uninterrupted electricity supply, an active maintenance programme, daily monitoring of their performance and quick response to irregularities as well as backup or alternative systems to support the air-conditioning load in case they are down for servicing. From the risk management point of view, unlike the latter four factors, electricity supply is an external factor that cannot be guaranteed. Fluctuation in the power level that results in stoppage of air-conditioning equipment is not uncommon even in well-developed countries. Long power outages could be catastrophic as they might lead to irreversible damage to collection items as a result of fast, large, changes in temperature and relative humidity (RH) towards the external environment if the air-tightness or hygrothermal stability of the storage are not good enough. Understanding storage environmental stability, especially during electrical power disruptions, is an essential part of the preservation measures and disaster preparedness necessary to protect valuable collections in cultural heritage institutions in the region.