Storage environment

The storage environment is the single most powerful preservation lever available, because it acts on every item continuously and without further handling. Temperature, relative humidity, light, air quality and physical security together determine the rate at which chemical decay proceeds. The chemistry is governed by an Arrhenius relationship: for many organic materials, each drop of roughly 5°C can approximately double useful life.

The modern consensus, reflected in standards such as ISO 11799 (document storage requirements for archive and library materials) and the PAS 198 guidance on managing environmental conditions, has shifted from rigid single set-points toward stable, appropriate ranges achieved sustainably.

Temperature and relative humidity

General mixed collections are commonly held around 16-20°C with RH in a 35-50% band, but the priority is stability: rapid cycling stresses hygroscopic materials far more than a steady value slightly off target. Different media want different targets - photographic and film collections benefit from cold storage well below 10°C, while very low RH embrittles parchment and adhesives.

• Avoid RH swings; aim to limit short-term fluctuation rather than chase a perfect number.
• High RH (>60-65%) invites mould germination and accelerates hydrolysis and corrosion.
• Very low RH desiccates and cracks organic materials.
• Cold storage dramatically extends the life of acetate and nitrate film and colour photographs.

Light and pollutants

Light damage is cumulative and irreversible, driven by total exposure (lux × hours). Store in the dark, eliminate UV, and control display exposure. Pollutants matter too: filter particulates and gaseous contaminants (ozone, sulphur and nitrogen oxides), and beware pollutants generated inside the store by poor-quality shelving, paints or enclosures - the reason materials should pass an Oddy test before use.

Sustainable, monitored control

Passive buffering (building mass, good enclosures, silica gel in cases) and well-sealed, well-insulated spaces reduce reliance on energy-hungry HVAC. Whatever the strategy, it must be monitored continuously with dataloggers so that drift is caught before it causes loss.

Key takeaways

• Cooler, drier, stable storage slows decay chemistry across the whole holding at once.
• Stability of RH matters more than hitting a single ideal set-point.
• Control light and pollutants, use passive buffering where possible, and monitor continuously with dataloggers.