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Measuring Effectiveness of Preservation and Security Programs

16. Measuring Environmental Quality in Preservation
James M. Reilly

The purpose of preservation is to safeguard cultural resources for the future without loss of value or usefulness in the present. In practice, this usually means preventing, retarding, or repairing deterioration. Preservation takes many forms, but none is so far-reaching or fundamental as regulation of the storage environment. Here, I will describe new technology from the Image Permanence Institute (IPI) for quantitatively assessing the storage environments of cultural institutions. This new approach is being tested at the Library of Congress in a pilot project to optimize both the quality and the cost of storage environments. The Andrew W. Mellon Foundation funds the project.

A broad definition of the environment encompasses a number of factors that affect the decay of collections, including light, pollution, vibration, radiation, and living organisms. Although all of these are worthy of attention, the two most important environmental factors in preservation are the old stalwarts, temperature and relative humidity (RH). Recent research has yielded an entirely new appreciation of the importance of these two factors in preserving cultural property. Yet the significance of environment transcends preservation. It is also a management issue having profound implications for the fiscal health and long-term success of an institution.

Whether designed for human comfort or for collection preservation, special environments are costly to deliver, all the more so in times of rising energy prices. Environment affects the productivity of staff and the performance of computers and other equipment. Less well appreciated is the fact that the future cultural and market value of collections will be determined by how well they are stored from now on. Better storage will mean less deterioration, which translates into higher future value and decreased costs for repair or reformatting. Managers of cultural institutions need to become more aware of their environmental conditions and to quantify the impact of those conditions on the collections.

The new measures of environmental quality developed by the Image Permanence Institute are based on the effects of storage conditions on the spontaneous decay of organic materials. To understand these conditions, it is necessary to explore the nature of decay processes and the way temperature and RH interact with objects. Temperature and humidity are always present, affecting the collections every minute of every day. Decay can occur through chemical, physical, or biological processes. All three depend heavily on environmental conditions. Biological and physical forms of decay are most influenced by relative humidity, whereas temperature is the critical factor for chemical deterioration. Libraries and archives have the most to fear from chemical decay, because modern information mediums are especially vulnerable to it. The classic example of chemical decay is the yellowing and embrittlement of acidic wood-pulp paper. Paper so weak that the page of a book cannot be turned without breaking has become a familiar sight in libraries around the world. Although the outward manifestation may be physical weakness, the underlying decay process is chemical in nature. Attack on the fibers of the page by acid is a chemical reaction, and, like all chemical reactions, it occurs at a measurable rate, by turns faster or slower depending on conditions.

Considerable scientific inquiry has been made recently into exactly what factors affect the deterioration rate of paper and other organic materials such as plastics, leather, dyes, and textiles—and to what degree. Although the specific problems addressed in the research projects have varied, the results of many of them point to temperature and RH control as the collection manager's best hope. The rate of decay is determined by temperature, concentration, pressure, and the presence or absence of a catalyst. To keep a book from becoming brittle, library managers cannot change the pressure (a constant pressure is provided by the atmosphere) or the presence of an acid catalyst (the papermaker supplied that), but they can regulate concentration and temperature.

Concentration—the amount of each substance involved in a chemical reaction—would seem to be a fixed quantity like atmospheric pressure, but it is not. Although the mass of a book does not change over time, the amount of water absorbed into the book changes with ambient RH. Water plays a direct role in almost every type of chemical decay, so its concentration becomes a primary rate-controlling factor. Ambient RH is therefore an important speed control for chemical deterioration processes. Over the entire range of RH from 0 to 100 percent, the overall rate of chemical decay varies by a factor of ten. The higher the RH, the faster the decay.

Although humidity typically gets the greatest attention from preservation specialists, it is temperature—not humidity—that in fact has the greatest effect on chemical decay. Temperature has the potential to speed up or slow down reaction rates by much more than a factor of ten. A large part of the preservation manager's task is to decide which kind of decay (chemical, physical, or biological) to worry about most. Chemical decay processes are a significant threat to library and archive collections because the information mediums found in libraries are primarily organic in nature and have a high rate of spontaneous decay at room temperature. Microfilm and pictorial films on nitrate and acetate plastic, early sound recordings, color photographs, acid-tanned leather, and acidic papers are but a few examples of such fast-decaying materials. For them, storage at room temperature means they have no hope to survive intact for more than few decades.

Ideas about the durability of library materials have been unconsciously shaped by the apparently good condition of many three- or four-century-old books. But we must bear in mind two key things about the condition of these venerable objects. First, they were made with inherently durable materials, such as parchment, whose life expectancy at room temperature was much longer than many of today's materials. Second, for most of their lives the objects were housed in cooler environments than they typically are housed in now. The low annual average temperature in unheated stone buildings of northern Europe, for example, together with effective means—albeit low-technology methods—to shield them from periods of high humidity, produced a much slower rate of chemical decay than any modern storeroom operated at pleasant and unwavering room temperature. The rare book room kept to tight tolerances at sixty-eight degrees Fahrenheit, 50 percent RH causes the books to deteriorate three to four times faster than their former home in the unheated church or manor house. As a consequence, as much deterioration has occurred in the last fifty years of "good" storage as happened in the previous two centuries.

Most people (including most preservation specialists) underestimate the influence that storage temperature has on the decay rate of organic materials. They underestimate both the negative impact of human comfort temperatures and the magnitude of the benefit gained from going only slightly cooler. Those who would never dream of parting with their home refrigerator or who do not hesitate to condemn as absurd the suggestion that meat-plant workers be allowed to work at room temperature, still maintain that the books, tapes, films, or pictures in their care are just fine at human comfort conditions. The overwhelming weight of scientific evidence says otherwise.

The foundations of IPI's quantitative approach to measuring the effect of environment on the decay rate of organic materials date from the development of predictive accelerated aging methods developed in the 1970s. These test methods were based on principles of physical chemistry and were designed to isolate and characterize the role that temperature plays in the decay of particular materials. As more and more results were published, preservation scientists began to realize the implications of the data and to formulate a larger theoretical framework that brought together both temperature and RH in a unified overview. In the 1980s, Donald Sebera of the Library of Congress created "contour maps" showing what combinations of temperature and RH yielded similar rates of decay for organic materials. He called these maps of equivalent environmental conditions "isoperms." Although this work was an influential and important advance, it did not provide a way to measure the decay rate for varying conditions.

In 1995, the Image Permanence Institute introduced the ability to directly measure and quantify environmental quality, at least as far as natural aging of organic materials is concerned. IPI's TWPI (Time-Weighted Preservation Index) is a way of analyzing temperature and RH data to determine how rapidly or slowly organic materials are decaying because of spontaneous chemical change. An algorithm integrates changing rates into a single number that represents the overall "preservation quality" of a storage environment. The TWPI of a storage space, for example, gives the number of years it would take for a typical "preservation problem" object such as acidic paper to become noticeably deteriorated in a given storage environment. In other words, the TWPI indicates the approximate lifetime of fast-decaying collection materials within that environment. Returning to our example of the rare book room at a constant sixty-eight degrees Fahrenheit, 50 percent RH, its TWPI would be forty-four years. This means that a new book printed on acidic paper would become noticeably deteriorated (discolored and brittle, but not turned into dust) in approximately forty-four years in such an environment.

In recent years, a number of off-site storage spaces have been constructed by major research libraries to relieve overcrowding and offer improved storage conditions. Many of these are designed to operate at around fifty-five degrees Fahrenheit, 35 percent RH. The relative humidity is slowly varied during the course of the seasons so that energy costs are kept to a minimum. The TWPI of such spaces is 163 years, nearly a fourfold improvement over our example above.

The value of the TWPI measurement is that it can integrate changing temperature and RH conditions and deliver one number that reflects the overall quality of the environment. The TWPI can be used to measure existing conditions and to give target figures for optimal conditions, including providing information for cost-benefit analysis of institutional environments. For example, the Library of Congress has used TWPI statistics in planning for its new off-site storage environments.

With funding from the Andrew W. Mellon Foundation, the Image Permanence Institute joined with the Library of Congress in 1999 to explore simultaneously optimizing both the cost of creating collection storage environments and the impact of those storage environments on the longevity of the collections. Working closely with the Preservation Directorate and with the engineering staff of the Architect of the Capitol (the "landlord" of the Library's buildings), IPI is collaborating with the energy-efficiency consulting firm of Herzog/Wheeler and Associates to apply IPI's environmental assessment technology to energy efficiency. Hardware and software developed by IPI will be used in this effort. The Preservation Environment Monitor, a data-logger specially designed for preservation use with funding from the Division of Preservation and Access of the National Endowment for the Humanities (NEH), will be used to gather the data, and Climate NotebookTM, a software program created for the purpose of environmental assessment, will be used to perform the analysis of that data.

The project in its second year concentrated on rare book storage areas in the Library's Jefferson Building and manuscript storage areas in the Madison Building. The goals of the project are to double the life expectancy of the collections while simultaneously reducing the consumption of energy. So far, we have collected data to establish a TWPI baseline and have made a close study of the air-conditioning equipment affecting the target areas. Although it is too early to see definitive results from the project, it is already clear that improvements in energy cost and collection longevity are possible. IPI and Herzog/Wheeler will be presenting information to the engineering, preservation, and collection staffs at the Library so that they can determine an optimum combination of human comfort, operating efficiency and collection preservation. Changes based on these decisions will be implemented, and the project will continue by monitoring and documenting the improvements made. A collateral goal of the project is to describe the management processes during the effort so they can be used by other institutions.

This paper has examined the theory and practice of new environmental quality measures in preservation. These quantifiable measures are the necessary first step toward having an integrated managerial approach to temperature and humidity conditions within cultural institutions. The measures provide a common basis for the engineering, curatorial, and preservation functions to work together toward the larger goals of serving society, maintaining a financially sound program, and enhancing the future value of cultural resource collections. [1]

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   September 15, 2008
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