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9. The use of vacuum chambers for recovery of water-damaged archival and library materials

9.1 Case histories

Apart from actual experience the best way to acquire familiarization with the subject is to see what others who hare suffered a disaster have done. Some of the case histories that follow may serve the purpose even though at first glance they cannot be called typical: thousands of documents and thousands of books in large institutions are involved. However, the basic difference between the overwhelming task of salvaging 50,000 books or 450,000 archival files, and a small disaster that wets a few books and documents is one of magnitude. The same steps taken by a large institution for recovery operations apply to a small, modest one as well.

9.1.1 Corning museum of glass library flood, corning, New York, June 22, 1972.

On June 22, 1972, the Corning Museum of Glass was submerged by flood waters as a result of a hurricane that swept the area. There were three days of continuos, heavy rainfall. A normally shallow river that flows through the city crested to nearly 30 feet (9.14 meters); the nearby Corning Museum had its main floor inundated to a level of five feet or one and a half meters (29).

Apart from the damage to a number of highly valuable objects in the glass collection, the library, which housed one of the best collections on the art, history and archaeology of glass, was badly damaged by the flood waters. Everything printed on the subject of glass had been collected for years and included books (a large number of them printed on coated paper), periodicals, documents, pamphlets, prints, catalogs, manuscripts, incunabula, medieval manuscripts and other: rare books.

On the morning of June 24 the sight that greeted museum personnel who entered the library was the devastation of books 90 sodden and swelled that the sides of the stacks were bent. Crowbars had to be used to dislodge the books. Other shelves had popped volumes into the muddy water; incunabula, manuscripts and rare books were submerged in it.

The difficulty of know ng what to do and where to start was eased by librarians who had read articles on the freezing of water-damaged books in order to stabilize them. But the obstacle of the moment was that electric power was out in the city. Furthermore, with so much damage to the community there was no gasoline available, no commercial transportation, no running water. And all were aware that if salvage operations did not begin immediately, mold infection would take place. So, with the librarians directing, members of the staff and volunteers began to gather the damaged materials.

Very little cleaning could be done without clear water. The books were wrapped in paper towels to hold them together and to separate one from the other. Plastic material would have been better but none was available. Then, using whatever containers on hand, the volunteers delivered the materials in their own vehicles to areas that did have electricity and placed them in domestic freezers. About 30 miles (40 kilometers) away cold storage facilities were found and used.

It took five days to pack the damaged collection of approximately 6,500 books, pamphlets, file catalogs, and other materials. Some 30 boxes of office files were packed for freezing as well. The card catalog had been ruined by water and thrown away. Fortunately, the shelf list although damaged was usable. The undamaged books were stored in a nearby college. By the time the last volumes had been packed and taken to storage freezers mold began to appear.

In August the undamaged books had to be removed from the college since the fall semester was about to start. A place was found in the city - an empty supermarket - where a library/ restoration studio was established. Also, the scattered frozen materials were placed in a rented freezer-truck which was parked next to the makeshift library/restoration studio.

A program charting the course to pursue was established which included the decision to send 200 rare books, in their frozen state, to a professional restorer. A chemist was also hired to supervise the work of volunteer workers. The chemist was also authorized to use new techniques to cut the time it would take for restoration of the damaged materials.

It was soon found that the freezer truck was so crammed there was no room for grouping and sorting the frozen materials. Also, the freezing components of the truck acted erratically causing partial thawing of its contests. The problem was solved by obtaining two large walk-in freezers. As each item was moved into the new freezers a record with copies was made of its condition. One copy remained with the item, one copy to the conservator, another to the librarian. When the item was taken out from the freezer the conservator noted the record which had the librarian's judgment on how to restore: restore fully by traditional methods, by new methods, or hold for later decision.

Thanks to a foundation grant a research scientist was hired for technical advice. The scientist and the conservator began to investigate drying methods. They focused on three:

a. Thaw the books naturally. (Pull the binding, wash to remove mud and stains, deacidify, dry, collate and store until the pages could be microfilmed).

b. Dry with a commercial dielectric drier. (The frozen book is placed between two electrode plates and electrical energy is shot through it. But it was soon found that the wet corers had to be removed because they made drying of the brook difficult, All metal objects, clips and staples, had to be removed to prevent arcing. Otherwise, the paper could be charred and burned. Since it was unknown what damage was being done to the paper, the valuable books were only thawed by this method but not dried).

c. Vacuum freeze-dry. (This technique was considered even though for the situation at hand it did not seem very practical. There were no vacuum chambers in the vicinity; it was not knows what would happen if this technique wee used of the large proportion of books printed on coated stock).

By the time the first year ended about 3000 books and boxes of files had been dried, cleaned, and made ready for microfilming. Also, the staff scientist had researched the chemistry of coated stock and run tests on wet books printed on coated paper in order to find why such books turn to solid blocks on drying. The scientist also established the parameters which could be used in the freeze-dry process (30).

It was decided to use the vacuum chambers located at Valley Forge, Pennsylvania, operated by the General Electric Company. Using the parameters established by the staff scientist for coated stock, the remaining frozen volumes were subjected to a process that took nine days to complete. At the end of that time 125 books had a condition that ranged from damp to wet. But 95 percent of the coated stock was saved, possibly marking the first time such success had been achieved. The five percent loss was due to text block solidification before the books had been put in the chamber for freeze-drying.

By December 1974 the restoration mission was over; some 6500 books had been dried and cleaned together with 30 cartons of documents and files.

9.1.2 Charles Klein library fire, Philadelphia, Pennsylvania, July 25, 1972.

The Charles Klein Law Library, located on the campus of Temple University in Philadelphia, was built originally in 1891 as a synagogue. The three story and basement building was taken over in 1953 by the University and renovated for use as a law library. The library held a 400,000 volume collection that included rare books on English and American law and documents that belonged to Benjamin Franklin. On July 25, 1972, a fire broke out on the third floor of the building, the cause was later thought to be of electrical origin, which resulted in its destruction along with a heavy loss of the library collection. The building had water-type extinguishers. There was no automatic sprinkler system installed; the manual fire alarm system was for alerting personnel in the building.

On that hot and humid day, at 1:45 pm, the Philadelphia Fire Department received a telephone alarm which resulted in the dispatch of four engines and two ladder companies to the Charles Klein Library which, at the time, was billowing smoke from the roof. The firemen first on the scene extinguished visible fire on the third floor but heavy smoke continued to develop in the area. A second alarm was sounded, then a third at 2:30 pm.

While the fire companies were busy on the third floor, a group of professors, students, and onlookers formed a human chain to salvage books shelved on the main floor. In this manner, the card catalog and about 3,000 volumes were saved.

The fire authorities halted the impromptu salvage operation when it became evident that the ceiling of the main floor was in danger of collapsing. At about 2:35 pm, not only the ceiling but the roof collapsed. Two minutes later the fourth alarm was sounded.

By now, master streams from ladder pipes and elevated platform apparatus were placed in service along with hand lines to contain fire. The combination was pouring 11,000 gallons (50,000 liters) of water into the burning building (31). A fifth alarm brought additional firefighters to the scene to replace those exhausted by the hot, humid weather. The total contingent was now 20 engine companies and one water supply company. At 3:15 pm, an hour and a half after the first alarm, the fire was declared under control.

The preliminary damage assessment, terse and concise was as follows: Water stands three feet deep (about one meters in the basement stacks and rare book room; main reading room books badly damaged, those toward the center burned when the roof fell in, others soaked with water from hose streams; some shelves and the entire Lucas Hirst collection of 21,000 books in a separate room are preserved by salvage covers placed over them early in the fire (31).

The company that carried insurance for the University obtained the services of two conservators from the Preservation Office of the library of Congress, and one from the Philosophical Library in Philadelphia. Up to this point no general salvage plans had been made. The first objective was to enter the basement, check the damage, and stabilize mold damage to the wet volumes. The high humidity and temperature found in the basement required prompt action. Thus, these volumes were given first priority.

On Friday afternoon, July 28th, emergency lighting and fans were set up in the basement to provide adequate working conditions. By midday, Saturday, volunteer crews began salvage operations. During the weekend some 30,000 volumes were removed and put in cold storage at 20 F below zero (-30 C). The majority of these volumes were from the three bottom shelves where the most water damage had occurred. Among the moldy, wet, and distorted books were many irreplaceable documents.

The volumes were wrapped in freezer paper and placed in boxer, loaded on four freezer vans, and transported to the cold storage facility. The books were not catalogued before packing. It was determined that at some later date the library staff could remove the books from cold storage and decide what course of action to take. The remaining Volumes in the basement were given eight sprayings of thymol to retard mold growth (31).

On Thursday of the following week the remaining 120,000 volumes in the basement were removed by volunteer crews. The books were indexed, boxed, and loaded on trucks. As mold growth had been stabilized with thymol, these books were transported to a controlled atmosphere facility (31). Thus, the stability of all the materials salvaged from the disaster was assured.

It was decided to freeze-dry the frozen materials. The insurance carrier, through its subsidiary salvage company which had arranged for the cold storage facilities, boxes and transportation after the fire, contacted the General Electric Space Simulation facilities at Valley Forge, Pennsylvania, for the possible use of a apace chamber. The appropriate arrangements were made and technicians at the space facility made some preliminary experiments in a laboratory chamber to determine the conditions that would be required for the frozen books to reach a dry state.

In order to freeze-dry the frozen books as economically as possible, a chamber was selected that would permit large volume drying. The chamber had a capability for easy horizontal loading and permitted an arrangement of shelves to be set up for the books. It was decided that these would be located spine down for better surface evaporation and closer contact with mesh heaters used to supply heat lost by sublimation. The chamber was equipped with a condenser that used liquid nitrogen as the refrigerant to trap the water vapor from the frozen books.

The processing took about five days including loading, unloading the shelves, and packing for shipment. For two of these days the books were in the vacuum chamber. About 3,500 books were treated at one time. Shoulberg (32), Applications Engineer-at the facilities, estimated that in the first batch 80 percent were dry; the second batch yielded 97 percent. The books that were not thoroughly dry in one batch were included in the next load.

During the process some experiments were carried out in the vacuum chamber by stacking the books spine down in boxes, and also putting the boxes directly on the shelves. Books in open boxes appeared to dry as well as those not boxed. An observation was made that if freezing is required and properly sized boxes are available, the boxes can be stacked spine down with paper in between and frozen in the boxes. The books can be dried directly in the type of chamber used at the facility with a great reduction in handling (32).

One final observation that relates to the hazards posed by water: In reference to the Charles Klein Law Library fire, E. Wiley of the National Fire Protection Association said that "The fire could have been controlled by an automatic sprinkler system so arranged as to transmit an alarm to a central station or to the fire department. Sprinkler flow would certainly have caused less damage than fire department hose streams." (31).

9.1.3 National personnel records fire, St. Louis, Missouri, July 12, 1973.

The National Personnel Records Center is a specialized organization that holds, for the most part, the service records of personnel, both military and civilian, who have been in the federal government. The records are housed in a six story building made of concrete with exterior walls of aluminum and glass. The building, which stands on a large tract of land, was completed in 1956 after a team of experts spent several months studying the spatial needs and facilities required to perform the task of a records center. However, the building had no sprinkler system. It appears that before the construction began the architect's surveyteam sought the opinion of government officials on the installation of a sprinkler system. Opinion was divided. However, the day was won by those who felt that damage from water was a greater threat than that from fire. The system was not installed (2).

On July 12, 1973, a few minutes after midnight, a fire of unknown origin broke out on the sixth floor of the building, In danger of destruction were the Center 's 120,000,000 personnel files stored in cardboard file boxes and file cabinets distributed throughout the building. The response of the fire companies was rapid. However, conditions were such that alarm after alarm went out and, eventually, firefighting units from 42 districts were on the scene (2).

Initial efforts to fight the fire consisted of a combination of snorkels pouring water from the outside, and hose companies doing the same from the inside. But conditions became so bad that the internal efforts were abandoned. The threat of a general spread of fire to the fifth floor was averted through the continuous flood of water to the sixth floor during July 13. By early morning of the next day, firemen were on the sixth floor. On the afternoon of July 15, heavy smoke began pouring from the southwest corner of the building. Firemen were dispatched up a ladder to direct more water there. By the morning of July 16 the crisis was over. Only one company of firemen remained. But the long days of recovery and rehabilitation were Just beginning (2).

Waters (15), who was an adviser at the scene of the disaster, gives a graphic description of the amount of water used and extended over the area: There was something like 60,000 gallons (272,400 liters) perminute on the fire, and a total of Just under 100,000,000 gallons (454,600,000 liters) on the whole area. For a total of three weeks after, there was water on every floor at a depth of one to one and half inches (about 25 to 38 millimeters a weight of 8,000,000 pounds (3,628,800 kilograms per floor. The drainage that was possible through these floors came down elevator shafts, escalators, and water hydrants.

Stender and Walker (2) estimate that only ten percent of the 22 million personnel Jackets stored on the sixth floor at the time of the fire could be recovered. As to the lowerfloors, more than 10,000 cubic feet (280 cubic meters) of water-damaged records were removed. Waters (15) estimated that about 450,000 glee were damaged below the sixth floor.

In any event, officials from the parent organization in Washington, the National Archives and Records Service, found themselves facing the largest records drying operation ever undertaken (2).

One of the first problems that had to be faced, in light of the tremendous amount of dampness in the building and the high summer temperatures, was attack by mold. The Preservation Office of the Library of Congress recommended spraying with thymol in solution.

In the meantime, temporary facilities were found at a nearby civilian records center where hastily constructed drying racks were assembled for the classic method of drying by exposure to air. As the damp records were assembled for transfer by truck, they were sprayed with thymol. It was found that the plastic baskets used for transporting milk containers were ideal for open-shelf drying. Soon an initial small supply of these baskets grew to some 80,000. Eventually all the storage areas were sprayed by a local exterminating company (33).

Some days after the fire, officials from the National Archives and Records Service learned of the existence of a vacuum chamber facility at the McDonnell Douglas Aircraft Corporation in St. Louis used for the national space program. The chamber was designed to simulate conditions in outer space during the ground testing of space systems used in the Apollo series of space shots (2). It was decided to approach the aircraft officials and ask for permission to try their vacuum chamber for drying the wet records.

With approval granted, some hurried experiments were under taken to see what would result with this particular type of drying operation. As soon as the initial tests were completed satisfactorily the drying of records proceeded on a priority basis. The now familiar plastic baskets were packed three quarters full in order to leave air space. Since they can be interlocked when placed one atop the other, they were packed on pallets and loaded on trucks for shipment to the vacuum-dry chamber. About 60,000 to 70,000 cubic feet (1680 to 1960 cubic meters) of materials were scheduled for drying in a chamber with 2,000 cubic feet (56 cubic meters) capacity. At this rate it would have taken several months to complete the task. However, use of the first chamber at the McDonnell Douglas Aircraft Corporation was supplemented eventually by the use of two additional chambers and, finally, by a similar chamber at a National Aeronautics and Space Administration facility at Sandusky, Ohio (2).

The vacuum-dry system was very effective. During a typical loading of one chamber holding 2,000 baskets about eight pounds (3.6 kilograms) of water were removed from each container. Thus, a total of nearly eight tons (7200 kilograms) of water was removed during each loading (2). Freeze-drying was initially considered a possible course of action for drying by sublimation; temporary arrangements had been made to place railroad freight cars on a siding near the records center in case they were needed to freeze and stabilize the water-damaged records. However, as things turned out, the nearby chamber facilities and success of the operation made the use of the freight cars unnecessary.

9.1.4 The Stanford Meyer library flood, Stanford, California, November 4, 1978.

The Stanford Meyer Library, part of the Stanford University complex, is located in the basement of the J. Henry Meyer Undergraduate Library. The basement library houses 400,000 volumes which are used by undergraduates for research in social science and humanities. The book stacks are on two levels of a metal-tiered construction.

On November 4, 1978, at 2:51 am on a Saturday, an eight inch (20 centimeters) water main burst at a point some 20 feet (about six meters) from the nearest wall of the Meyer building. Water from a crack along the main filled a large excavation, part of construction work in progress, and then found its way through a number of holes in the building wall which had been drilled for the installation of drains and pipes.

Water entered the building and flooded the floor level of the upper metal-tiered stack which had a surface of 5,000 square feet (460 square meters). From here the flood water dripped to the floor below and soaked, to varying degrees, more than 50,000 volumes. Thanks to an emergency call to a plumbing crew working on the campus, the water was turned off 20 minutes after rupture of the main.

As the water traveled the short distance to the basement wall, it carried with it fine silt which was deposited over the floor on both metal-tiered levels. Many books had swelled to the point where they were Jammed into the shelves; others had popped onto the silt-covered floor. There were never more than a few inches of water standing on the two floors, However, the water dripping like heavy rain for several hours on the lower level did most of the damage.

The building 's electric power was kept on in order to start cleaning operations with sponges, mops, and large vacuum cleaners designed to operate in wet or dry conditions. Most of the silt and water were removed by 8:00 am, the same day of the disaster.

An initial meeting was held at 6:00 am to carry out certain steps already developed by Stanford's disaster planning team. The steps included the appointment of a disaster coordinator, the maintenance of the building air-handling system to maximize the circulation of cool air to reduce humidity as quickly as possible, and to freeze the materials right away (4).

Cold storage facilities were located a short distance from the University. Some 3,000 books cartons and milk crates were initially ordered. But 1,500 more were obtained because the books, wrapped in freezer paper, were packed one layer deep and spine down to avoid damage. Cartons were packed three high to avoid collapse of the damp boxes; 160 pallets used to carry the boxes were sent to the freezer. The boxes remained on the pallets until they were removed at the vacuum chamber at a later stage.

By 9:30 pm, Sunday, all materials had been removed to the freezer. Forty-three hours had elapsed from the first alarm until the final freezing. There was no evidence of mold. At -20 F (-28.9 C) the wet materials were stabilized and safe until decisions on drying techniques could be made (4).

The literature was reviewed with particular attention to past disasters, for example the National Personnel Records Center fire, where vacuum-drying had been used for mass drying of water-damaged documents. It was evident to University officials; that for the frozen books, freeze-drying was the best method to employ They knew that machines for this specialized drying are used in scientific laboratories, food processing, and in the aerospace industry. So, a search began. Several were located which might have been suitable for a small collection of water-damaged materials, but not for over 50,000 books.

Finally, a facility was found at the Lockheed Missiles and Space Company at Sunnyvale, near the cold storage freezer where the books reposed. Several vacuum chambers were possible; the one selected had walk-in accessibility and sufficiently large, 18 x 18 x 36 feet (5.5 x 5.5 x 10.9 meters), to take metal racks capable of holding 5,000 frozen books with provision for a surface heating system. The vacuum chamber had a ten by ten foot (3.05 by 3.05 meter) condensing panel, cooled by liquid nitrogen, to trap the water vapor from the frozen books.

A trail run was made to determine the best method for housing the books: in milk crates, or books upright in their normal position, flat on the shelves, or simply in boxes. The books selected - discarded ones - were soaked in water then frozen. They were placed in the chamber to freeze-dry. When the drying cycle was completed the dried books turned out to be brittle - less than two percent moisture. Ideal moisture content is between five to seven percent (33). The books would require stabilization in a normal environment.

The test also proved that the manner of housing made no significant difference, but wrapped books dried more slowly than partially wrapped books. It was also found that books placed upright looked better physically. So, a decision was made to dry the books upright, spines to the back, supported snugly by size (4). Heat would be applied to the spines, and thermocouples placed in some of the books to record the drying state.

On February 5th the first load, 5,000 frozen books, was transported to the chamber and placed on the shelves. It was estimated that about four days would be required for all phases of the drying operation.

The first step was to evacuate the chamber to less than 4 torr to freeze any free water in the books. Then for the first 56 hours the condenser panel was to be kept at less than -150F (-101C) with the vacuum in the 10 -3 torr range. The book temperature would not exceed 100 F (37.78 C). At the end of this period the power required to maintain these conditions would be turned off and the chamber brought to normal pressure. Ice from the condenser would be removed and books checked for dryness. Those found to be dry would be placed in a non-heat area of the shelves. Next, the chamber would be re-evacuated to a pressure of 10 -1 torr for about 26 hours with the book temperature at 100F. This stage would terminate when about one half of the thermocouples read at temperatures above 55 F (12.78 C). The chamber would then be brought to normal pressure. Any books still frozen would be placed with the next load to dry (14).

With much learning on-the-job, by February 12th some 10,000 books a day, two days a week, were being dried by sublimation. Care had to be exercised with the dried volumes because of their fragility in that state. March 12th was the date of the last load to leave the chamber. Most of the books were placed on shelves in a vacated school site near the University. The conditions established there enabled the books to stabilize to six percent moisture content, as measured by an Aquaboy (35), in about five weeks after shelving.

By the end of the year the operation was closed. Much work had been done since the flooding of over 50,000 volumes: besides freezing and drying, the cleanup of the flooded library, repairing and restoration of books, among other details. One thousand books were bound, 27 items were microfilmed, 12 volumes would require searching for replacement, 34 books were discarded due to the flood, three were not replaceable. All other items were returned to the stacks (4).

9.1.5 Taylor institution library flood, oxford university, January 1979

During the month of January 1979 a water main burst at the Taylor Institution Library and flooded the basement stacks where approximately 2,000 books, some rare volumes from a collection of Slavonic literature which included early 16th century examples, were water-damaged in degrees varying from damp to very wet.

A small number of slightly damp books were left on the shelves to dry. The moderately wet, about 1800, were dried in the classical manner by standing them upright and slightly open in a current of dry air. The remainder, too wet to stand upright, were put in plastic envelopes, frozen and kept in a commercial chest-type freezer at -18 C (-0.4 F). There was now time to seek a safer and quicker method for their drying.

Laboratory scientist at the Atomic Energy Research Establishment, at Hartwell, where industrial drying was being researched, were approached with the problem. It was decided to adapt a vacuum chamber, 48 inches in diameter and 56 inches long (122 centimeters in diameter and 142 centimeters long) to do the job. Shelves were built into the chamber on which the frozen books could be placed. The books varied in size and material: rag paper to wood pulp, covers that ranged from vellum to leather, some with paper or plastic covers on ordinary boards. The books contained from 35 percent to 100 percent of absorbed water as determined by weighing during the drying process and compared with the final weight of each book (36).

Initial trials were undertaken using a small quantity of frozen books chosen at random; vacuum pressures were varied, different amounts of silica gel in trays were used to absorb the water vapor in the chamber. Finally, the conditions for the production runs were: A vacuum pressure of 745mm Hg in the presence of two trays each with four kilograms (8.8 pounds) of silica gel which was renewed each 24 hours. Ten grams of thymol crystals in a dish were used to prevent mold attack. It was found that small books reached a dry state after 80 hours, the larger after 225 hours (36). As the books were removed from the chamber, they were placed in a normal atmosphere for about 48 hours to stabilize them.

The condition of the dried books varied. There was light wrinkling of the pages with some staining due to metallic salts in the flood water. There was damage to the spines, hinges and joints caused by the initial soaking. The vellum and leather covers were affected by the drying: The vellum became brittle when dried out; the leather suffered where stretched over warped boards. The more modern materials used for covers recovered well, except where plastic materials were used. These warped badly on drying.

Of the 115 books sent to Harwell for drying, 43 needed to be rebound (36). It must be emphasized, however, that materials requiring rehabilitation after vacuum drying were already damaged at the time of freezing and drying.

9.1.6 Regional office of income security services fire, Winnipeg, Canada, January 22, 1981.

On January 22, 1981, a fire gutted the three story building in Winnipeg that housed, on the upper floors, a regional office of Income Security Services. Also, in the same building, there was a second social service organization: The Jewish Child and Family Service. The two services had up to 600 linear feet (183 linear meters) of records. During the fire about 80 file storage cabinets went through the floors as the firemen battled the blaze.

The salvage operation began when the active files of the Income Security Services were moved to the basement of another building. About ten percent of the files were relatively unharmed, but a large amount of file cabinets had swelled with the water; crowbars had to be used to pry them open.

Mold infection and the fusion of wet documents became the immediate concern of the archival personnel. So, it was decided to air-dry on the spot. Heat was reduced, work tables were set up, new materials for storing the dried documents were obtained. Large fans were placed in strategic locations to blow air over the documents. With relatively dry air in the basement, about 30 percent relative humidity, the manual drying process, aided by hand-held hair dryers, progressed satisfactorily.

Attention was now turned to the closed but wet files in some 150 file drawers. Plastic milk crates were obtained from a local dairy. It took over 400 to hold about one cubic foot (0.028 cubic meters) of loosely packed documents in each crate. On January 29th the crates, which had been stored in a cool place, were moved into a building with no heat. In a cloy where winter temperatures range from -7 C to -28 C (19.4 F to -18.4 F) the wet documents were effectively frozen.

Locating a facility for the drying operation was the next problem to solve. A telephone lead provided the required information: The Canadian Forces Base at Winnipeg had a high altitude vacuum chamber. Soon the archives authorities were in touch with the staff of the School of Aeromedical Training. It was discovered that members of the staff had experience in drying wet documents in such chambers. At the same time, experts at the Library of Congress were contacted for advice.

The Canadian Forces chamber is 20 years old with an interior that measures 24 feet long by 8 feet wide and 6 1/2 feet high (7.32 meters long by 2.44 meters wide and 2.0 meters high) (37). The chamber was of sufficient capacity to permit the entire load of frozen documents in the crates into it. This phase was completed on February 3rd.

The chamber lacked a heat source to replace the heat lost during evaporation. As a consequence, the drying process was slow. After four days the vacuum chamber, which had been at a simulated altitude of some 80,000 feet (24,400 meters), was reduced to normal pressure to run a check on the documents. The process was working, but they were quite damp. So, the drying cycle was repeated. Three days later over half of the documents were dry.

The remaining damp documents were distributed among additional crate. in order to facilitate drying; the load went back into the chamber and its simulated altitude. On February 12th, after nine days under vacuum pressure, the chamber was brought down to normal pressure. The small amount of slightly damp documents were easily air-dried with the help of fans.

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