Risk-Based Indoor Microclimate Monitoring for Preventive Conservation: Application of HMR and PRD Indices at the National Historical Museum of Greece

Museum collections are highly sensitive to fluctuations in temperature (T) and relative humidity (RH), which drive physical, chemical, and biological deterioration of heritage objects. In Mediterranean countries, where outdoor climatic variability is pronounced, indoor microclimate management poses a persistent challenge for institutions housing diverse and often irreplaceable collections. This study presents a two-month microclimate monitoring campaign in an exhibition hall of the National Historical Museum of Greece (NHM), housed in the Old Parliament House, Athens, to assess preservation risk using two standardized conservation indices.

Continuous T and RH data were recorded using a Testo 160 TH data logger (±0.5 °C, ±3% RH accuracy), capturing the diurnal and short-term variability in the indoor environment and allowing reconstruction of representative hourly and daily T–RH profiles. The dataset was analysed using the Heritage Microclimate Risk (HMR) index and the Predicted Risk of Damage (PRD) index. HMR combines the deviation in mean conditions from standard conservation thresholds (HMRenv) with the amplitude of short-term oscillations (HMRosc), producing a composite score ranging from lower to upper-threshold risk. PRD translates the HMR value into a probabilistic estimate of material damage, with reference thresholds drawn from EN 15757 and UNI 10829 and material-specific coefficients applied to the collection typologies present in the hall.

Results identify the dominant risk drivers within the monitored space, quantify the relative contributions of mean-condition deviations versus oscillation-induced stress, and highlight periods of elevated preservation risk during the monitoring window. By translating continuous environmental monitoring into a quantified, comparable risk metric, the HMR–PRD approach illustrates how risk-based assessment, grounded in real-time monitoring data, constitutes a pillar of sustainable preventive conservation, enabling targeted, low-cost decisions in Mediterranean museum environments without requiring extensive infrastructure.