The Ounce: Don't Dry This at Work/Home

Welcome to The Ounce, an occasional missive for Harvard Library colleagues from Preventive Programs in HL Preservation Services.

The Dry Humidity Season: November-February

During the fall and winter season, indoor humidity levels drop, presenting risks for library and archive collections. Humidity below 40% is drying and can cause organic materials to shrink, warp, crack, or become brittle. These changes can be permanent or require conservation treatment to resolve.

If humidity drops lower than 30%, some materials are even more susceptible to these changes. If low humidity is persistent, consider storing or working with more vulnerable items in a location with better humidity control. Preservation Services and your building’s facilities manager can help.

Tracking and Analyzing RH (Relative Humidity)

The human ability to detect changes in humidity can vary and is not recordable. So, we recommend using dataloggers to collect environmental information about your collection storage areas. Preservation Services can assist with the installation and analysis of humidity and other environmental conditions in your library, as well as assess which types of collections are more vulnerable. Your building’s facilities manager can explain what the air-conditioning system is capable of doing to keep humidity moderate and stable.

A small device to read temperature and relative humidity.