This past week we installed ten Preservation Environment Monitors (PEMs) purchased from the Image Permanence Institute (IPI) through the generous support of a National Endowment for the Humanities (NEH) Preservation Grant for Small and Medium Sized Institutions. The devices will be used to monitor and assess the environmental conditions of collection storage spaces in use by Special Collections. The results will help us to make decisions about the distribution of materials and will allow us to better manage the long-term preservation of the collection for the benefit of our users well into the future.
Raw data collected from the PEMs can be uploaded to PEMdata, a web- based preservation management tool developed and maintained by IPI. As noted on the organization’s website, the software can be used to organize temperature and humidity data, graph and interpret that data, and generate reports. Interior temperature, humidity, dewpoint, mold risk, and other parameters can be viewed in line graph form and compared to graphs of exterior conditions for the same period.
Algorithms developed by IPI use the data to determine the risk of various sorts of deterioration for a range of library materials that may result from the observed environmental condition through natural aging, mechanical damage, mold growth, and metal corrosion. These deterioration risks can be combined and displayed as a time-weighted preservation index or TWPI, a single number meant to represent the “approximate length of time, in years, that vulnerable organic materials would last if every time period in the future were just like the one during which the TWPI value was measured.” Calculators on the site allow one to make virtual changes in environmental conditions and view the effect on the TWPI.
The ten new monitors are added to one we have had for nearly a year. It has collected data in one of our open stacks locations in Special Collections. A look at the data collected shows that the space being monitored offers less than ideal conditions for the storage of many types of materials, with a TWPI of 42 years. The risk of deterioration from natural aging is due to higher than recommended year-round temperatures and, to a lesser extent, elevated relative humidity levels during the summer months. Heightened temperature and humidity can accelerate the rate of decay of many materials, including film, photographs, magnetic tape, and books and papers produced from the mid-nineteenth century to the late-twentieth century. With this information in hand, one would ideally make changes to lower the temperature and summertime humidity levels. If this is not possible, the space could be used for storage of materials that are least likely to suffer from storage under moderately elevated temperature and relative humidity.
On the positive side, temperature was maintained in this space at a fairly consistent level and humidity levels did not reach the point at which mold growth could be supported, a constant worry in library collections housed in older buildings. Additionally, a comparison of the exterior and interior dewpoint temperatures shows that the building HVAC system functions in removing moisture from the air during the summer and adding it during the winter.
This type of data will eventually be available for all of our Special Collections storage spaces and will allow us to make informed decisions about the placement of materials and the improvement of our environmental systems.