UNDERSTANDING SUCCESS
Measuring Effectiveness of Preservation and Security Programs
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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
textilesand 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.
Concentrationthe amount of each substance
involved in a chemical reactionwould 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 temperaturenot
humiditythat 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 meansalbeit
low-technology methodsto 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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