The Massachusetts Board of Library Commissioners (MBLC) is an agency of the state of Massachusetts responsible for organizing, developing, coordinating and improving library services throughout the Commonwealth. Gregor Trinkaus-Randall is the Preservation Specialist at MBLC where he implements the statewide Preservation Program, Emergency Assistance Program, and Environmental Monitoring Program. As part of the latter program, Trinkaus-Randall gathered indoor environmental data from storage and display areas in over 400 libraries and historical institutions in Massachusetts, as well as outdoor data for every site, between 1996 and 2010. Spectrum dataloggers collected temperature and relative humidity data for periods of five months, in time frames that spanned the heating and cooling seasons of the year. Trinkaus-Randall reviewed the data and provided each institution with a report that summarized the environmental conditions and offered preservation advice based on his analysis. From 1999 on, IPI's Climate Notebook® desktop software was used for data management, reporting and analysis.
The Research
The systematic collection and analysis of both outdoor environmental data and indoor data from cultural institutions on such a scale presented a unique opportunity to extract information useful to both MBLC member institutions and to preservation programs nationwide. In 2008, Trinkaus-Randall approached IPI director James Reilly about developing a research project to extract trends and develop new methods for environmental analysis from the data. It was decided to create a general overview and realistic picture of the environmental conditions in these institutions. The entire body of data and associated information was transferred to an on-line website which would be accessible to all 400 institutions. The data would be analyzed using IPI's quantitative measures of specific risk to collections. A set of benchmarks would be created allowing institutions to gauge their performance and identify areas in need of action to improve preservation quality. Finally, IPI would create a detailed statistical analysis of the outdoor and indoor environments in Massachusetts by season, region, and institution type. The project was funded by MBLC, began in October 2008 and was completed in September 2009.
Findings Regarding the Role of Outdoor Conditions
Massachusetts has a humid continental climate characterized by hot summers and cold winters. The state receives about 40" of rain annually, fairly evenly distributed throughout the year. Summers are warm with average high temperatures in July above 80°F and lows above 60°F. Winters are cold, though less extreme on the coast and colder as you move inland. Typical winter temperatures in the Western Region average 22°F while the Cape and Islands in the Southeastern average 32°F. This variation is due to the moderating effects of the Atlantic Ocean. Overall the mix of weather throughout the year averages out to about 50% clear, 25% cloudy and 25% wet.
The primary concern seen in the outdoor data is dampness year round. Moisture levels are highest in the Southeastern, Central and Western Regions during the fall season. This climate promotes mold growth and dimensional change and increases the rate of natural aging.
Indoor Conditions
Inside the institution, collection risk comes primarily from high indoor humidity, leading to mold and an increased rate of chemical decay or natural aging. This risk is especially high for institutions in the Southeastern (Cape Cod) region, where proximity to the sea leads to a high moisture content of the air, which translates to high indoor humidity. Any location that experiences high outdoor humidity in the late summer and early fall has to be especially careful to avoid cooling the air too much during this time. Too much cooling will drive the RH up to mold-inducing levels. In addition, during the low RH winter season, institutions should avoid over-heating storage and display areas. The high temperatures work against collection preservation by drying objects out excessively and also driving up energy costs needlessly.
How Massachusetts Institutions Dealt with the Mold Risk
IPI analyzed a total of 833 indoor datasets from libraries and cultural institutions in Massachusetts. Fourteen indoor datasets (from twelve institutions) had a Mold Risk factor greater than 1.0 (which indicates that mold would have germinated in that space during the measured period). The fact that this represents only 1.6 % of the total is encouraging. One significant commonality among these fourteen was the fact that twelve were from the fall season. Looking more closely at the data, nearly all the mold risk occurs in the months of August through mid October. This is the time when the moisture content of the air outdoors is relatively high (dew points of 60°F and above). The indoor temperatures of the datasets where mold risk was observed was relatively cool (70°F or below). The combination of high dew point and low temperature caused the RH to soar above 70% (sometimes much higher). In most cases the mold risk could have been avoided by heating the air slightly (or by cooling it less) during those six to twelve weeks when the dew point was high but the indoor air was cool.
The fourteen locations with a Mold Risk of 1.0 or greater (6.46 was the maximum, indicating that mold spores would have germinated six times over) were actually similar to many other spaces, especially in the fall season in the Southeastern Region, but with a few key differences. The fourteen had an average dew point of 47°F, while all the fall Southeastern datasets had a dew point of 45°F—not a large difference. However, the fourteen were significantly cooler in average temperature: 65°F for the mold risk locations, while the non-mold risk spaces were warmer at 69°F, enough to keep them out of danger from mold.
Valuable Conclusions!
Some simple rules of thumb for reducing the risk of biological decay are:
- Keep excursions above 65% RH to a few days or less
- Avoid high RH at moderate temperatures – use dehumidification to achieve this
- Keep summertime and early fall dew points as low as possible
As noted elsewhere in this issue, it is important for institutions in any region with a cool, damp fall is to pay close attention to controlling temperature from August through October—when the amount of moisture in the outdoor air is high. Consider both temperature and RH and don't assume that cooler temperatures will always be better for preservation.