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Part 2: Recovery from Disasters
Presented at "Emergency Preparedness and Disaster Recovery of Audio, Film, and Video Materials"
A Library of Congress Symposium -- September 21, 1995
by John Van Bogart
Slides for Part 1: Recovery from Improper Storage
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Part 2: Recovery from Disasters. The next several slides discuss methods to recover magnetic tape and optical disk from water damage, fires, shock, mold, dust, stray magnetism, and theft.
Tape can be thought of as a high quality paint coating on a plastic film. It does not have the same susceptibility to water that paper does. Chemically, tape is much more similar to microfilm and motion picture film than it is to paper. As a general ru le, in salvaging magnetic media that has been subject to a disaster, use the same methods that you would use for microfilm or motion picture film. DO NOT automatically use methods that you would use for paper.
Magnetic tape is chemically similar to film stock. Both have historically used similar substrates (currently PET; in the past, cellulose acetate). Magnetic tape will not deteriorate in water like paper will. Magnetic tape will not soak up water like a sponge like paper will.
Magnetic tape is chemically dissimilar from paper. A drop of water on magnetic tape will bead up and stay beaded. A drop of water on paper may initially bead up, but will eventually be absorbed by the paper.
Whereas paper is susceptible to damage by water, magnetic tape is more susceptible to damage by extremes in heat and cold and dust and debris.
In prioritizing an archive that has been devastated by a disaster, it is more important to save the wet books that it is to save wet tapes. If the water is clean, tapes can remain wet for several days without immediate attention. If the water is dirty, or salty, the tapes should be rinsed with fresh water ASAP, but they do not need to be immediately dried.
In prioritizing the tape recovery, older tapes should be treated before newer tapes are. The older tapes will be less resistant to damage by moisture than will the newer tapes. In addition, tapes on a cellulose acetate backing should be cleaned and drie d before PET backed tapes are recovered.
Some very old tapes used a paper substrate. These tapes should be treated as paper rather than as plastic film. They should receive immediate attention and be dried ASAP.
Previously it was mentioned that tapes hydrolyze in the presence of water resulting in the "sticky shed" phenomenon. This would suggest to someone that water would be a rather destructive agent for magnetic tape. While it is true that water causes tape binders to hydrolyze, this reaction occurs very, very slowly. It can take decades for tapes to hydrolyze to the point that they have a "sticky shed" problem under normal storage conditions.
If a tape gets wet as the result of a disaster, it is not immediately in danger, unless the water contains an agent that is harmful to tape, such as an organic solvent or a corrosive agent (sea water). Paper is much more susceptible to permanent damage a nd should receive immediate attention. A tape rinsed in clean water can sit for several days while wet paper is being recovered.
Recovery methods used for paper should not automatically be applied to the recovery of magnetic tape. Not all methods used to recover wet paper are appropriate for tapes.
Some paper recovery methods involve the use of heat or freezing. When a tape pack is heated, tape pack tension increases which may cause distortion of the backing. Print through can also become a problem in tapes exposed to elevated temperatures. Cooli ng a tape will loosen the tape pack making the tape more susceptible to pack slip. This may open up spaces between tape windings allowing water, dirt, and debris to enter the tape pack. Extreme cold (below 5 C) has also been known to result in lubricant migration to the surface of the tape.
When recovering and drying tape it is best to avoid the use of those methods which use excessive heat or cold as part of the recovery procedure.
Some recovery methods for paper involve freezing of wet materials. This solidifies the water so that it can no longer infiltrate the paper and cause damage. Freezing of books is helpful in preventing distortion, blocking, and decomposition which would o ccur if the books were allowed to stay in contact with liquid water.
Freezing of tapes can actually damage them. The tape pack may loosen up sufficiently on cooling to allow water to get in-between the tape windings. On freezing, this water will expand and may distort the tape backing. Freezing of tapes can also cause m igration of lubricants in the binder to the surface of the tape. These lubricants may not be reabsorbed once the tape is warmed to normal storage conditions.
Since magnetic tape materials are not effected by water the same way books are, it is OK to keep them wet and at room temperature before they can be dried. The tapes should not be allowed to remain in dirty or salty water for too long as the mud or salt water may contain components, such as organics or corrosives, which may degrade the tape. Once the tapes have been rinsed with clean water, attention can be given to other archive items in more urgent need of recovery.
If a tape has been exposed to fresh water, rain, sewage, mud, or sea water as a result of a disaster, it is important to keep the tape wet until a recovery effort can begin. DO NOT allow the tape to dry out as any sediments in the contaminating water wil l dry onto the tape and be more difficult to remove. Tapes can be kept in a sealed plastic bag with a wet towel or sponge to keep them from drying out; however, unless kept cool, these tapes may experience molding if not treated within a week or two. Ta pes can be immersed in water for a longer period of time without a possibility of molding.
If a tape has been exposed to fresh water, it just needs to be rinsed in distilled water and dried. The tape can be carefully blotted dry with a lint-free towel, assuming that no tape edge damage will result from this action, and air dried. If the tape pack quality is poor so that contact with the tape could cause tape edge damage it is best not to try to remove any excess water from the tape. Dry the tapes in a reduced humidity environment (~20% RH or less) at room temperature. Vacuum drying is also acceptable at ambient temperatures.
If a tape has been contaminated with mud or sewage, it is important to rinse off the tapes as soon as possible. The mud or sewage could contain organics or other contaminants hazardous to the tape. A complete recovery effort is not important at this sta ge. Once rinsed, the tapes can sit while other higher priority items can be addressed, such as books and paper.
When recovering muddy or sewage contaminated tapes, it may be necessary to use soapy water. Not all debris may rinse clean with the use of plain water. Use just enough of a mild detergent (dish washing liquid that is dye free and perfume free is OK) tha t is required to remove any oils or greases from the tapes.
In any wet tape recovery effort, it is always important to use a distilled water rinse prior to drying. Hard water or other sediments left on the tape can cause dropouts and head clogs as the debris gets between the tape head and the tape.
There is no harm in too low of a humidity for tape treatment. (Low humidity is only a problem if the tapes are to be played at low humidities). Use of a winder-cleaner will not be necessary unless the water has infiltrated the tape pack because (1) the wind tension was too low, or (2) the tape had several popped strands.
In the recovery of tape from brackish or sea water, it is important to rinse the tapes as soon as possible. The salts in sea water are very corrosive to reduced metal based tapes such as MP (metal particulate) and ME (metal evaporated) tapes. Oxide base d tapes are not at as great a risk from attack by corrosives. However, unless you know that your collection contains no MP and ME tapes, or you can tell the difference between your oxide and MP/ME tapes, it is best to rinse all tapes ASAP. MP and ME tap e are used extensively in high grade 8mm video, digital video, and digital data applications.
If the tapes have been submerged for an extended period of time, or have been recovered from the sea floor, or have been allowed to dry out after recovery from the sea, it may be necessary to place the tapes in a mild hydrochloric acid solution to remove any calcium carbonate deposits on the tape. The degree to which the tape is contaminated with such debris will depend on how long the tape was exposed to the sea water before recovery procedures could begin. Failure to remove these deposits could result in subsequent dropouts from this debris.
Finish the cleaning with a rinse in distilled water, and allow to dry.
Tapes which have been through a fire can have water damage, heat damage, and soot damage.
Tapes which have experienced heat or fire damage can be respooled onto new tape reels if the old reels have warped or charred. Tapes in cassettes may need to be transferred to a new cassette if the cassette shell has warped.
Soot can be vacuumed from the tapes or cassettes. Direct contact with the tape pack should be avoided as this can cause tape edge damage. Soot which cannot be removed by vacuuming can be wiped from the cassette or tape pack with a lint-free cloth dampen ed with distilled water.
If the temperatures in the fire were excessive, the tape may have gotten warm enough for the binder coating to "melt" causing the tape winds to stick together. This is known as blocking. There is no way to recover a badly blocked tape. If you try to un -spool the tape, you will just rip the coating from the backing in enough places such that the tape will be unplayable. The only way to recover recorded information in this case is to have backed it up on another tape in another location.
Proper fire prevention devices, such as sprinkler systems, can prevent the heat of the fire from getting too high and can prevent tape blocking. The recovery procedure will the consist of a "wet" tape recovery, but in most cases the tapes should still be playable.
Remove dust from a cassette by vacuuming, brushing, or wiping with a damp cloth taking great care not to damage the tape edge.
First, try vacuuming as much of the debris from the tape reel as is possible, avoiding direct contact with the tape pack. Do not remove the debris by blowing as this will just relocate the contaminants onto another tape or recorder.
If debris cannot be removed by vacuuming, try removing it next with a soft brush. Wipe off any remaining debris with a dampened cloth. Avoid getting the tape wet if it is not already wet.
If the tape is excessively dirty/dusty, use of a winder-cleaner may be required to remove debris. Poorly wound tape packs may require use of a tape winder-cleaner to remove debris that has worked its way into the tape pack crevices. Note -- If high qual ity tape winds have been maintained, clean-up will be much easier.
Before beginning any recovery effort involving mold/fungus, it is very important that recovery personnel are properly protected from contact with and inhalation of mold spores and debris. At a minimum, staff should be equipped with gloves, non-ventilated or filtered eye protection, dust/solvent mask with a HEPA filter, and a protective smock or lab coat. Inhalation of mold spores and bodies can be a significant health risk.
Moldy tapes should be isolated from the rest of the collection and placed in a low humidity environment (the lower the better) until recovery efforts can begin. Keep the tape at a humidity below 50% RH and at a temperature below 75 F until recovery proce dures can begin. Lower humidities (e.g., 20%) are OK.
Begin removal of the mold by vacuuming. The vacuum should be fitted with a HEPA filter to prevent the spread of small particulates which are not trapped by a conventional vacuum bag. DO NOT BLOW the debris from the tape as this will only lead to further contamination of archive materials. Furthermore, avoid breathing any of the mold while performing the recovery procedure. It is advisable to wear a dust mask during the recovery procedure.
Use of a winder-cleaner will be necessary to remove all mold debris. Mold is invasive and will eat its way through the binder and into the tape pack. A superficial cleaning of the tape pack will not be sufficient to remove all debris.
In most cases, it will be necessary to transcribe the tape. In the cleaning operation, only the "fruiting bodies" will be removed. The mycelia will still be alive and living in the tape binder. They cannot be removed with a simple cleaning. Given the right conditions, the tape will exhibit mold growth a second time if returned to the archive. It has been reported that treatment with radiation (that used to kill bacteria on meat and produce) can successfully destroy any living mycelia eliminating the need to transcribe the tape.
To recover from shock: If the shock was mild, the tape may just require re-tensioning and re-spooling to correct any shifts in the tape pack wind. If the tape reel or cassette has been damaged, the broken pieces should be replaced. In more severe forms of shock, re-splicing of the tape may be required. Use a high quality tape for splicing which will not ooze adhesive out onto the tape surface over time. If the tape has been crushed or wrinkled, the backing can be reformed by re-spooling and allowing time for relaxation of stresses (several months may be required).
If the tape is severely wrinkled, or it desired to recondition the tape quickly, thermal reconditioning of the tape can be performed. Small sections of the tape (1-2 feet) are un-spooled from the tape reel or cassette and laid magnetic side down on a smo oth Teflon sheet. An iron at a low setting is used to press down on the tape from above on the backing side of the tape. The brief heating allows stresses in the backing to relax more quickly and flattens the tape. No back or forth ironing motion is re quired, the iron is pressed down on the tape, but remains stationary during the thermal reconditioning treatment.
To recover from stray magnetism: A tape that has been demagnetized inadvertently cannot generally be recovered with a commercial recorder. A special recorder capable of reading information from a tape with a significantly reduced signal-to-noise ratio w ould be required. These are generally not commercially available -- such a recorder would need to be custom built.
To recover from theft: The only way to recover from the theft of a tape is to have a second source of the information available. Maintaining a second copy of the information at a second location is the only way to guard against theft.
In general, when cleaning tapes, the tapes may be sufficiently cleaned by cleaning the exterior of the reels or the cassettes. It is not always necessary to use a winder-cleaner to clean the tapes. It is not always necessary to disassemble the cassettes to clean them. If enough of the debris can be removed without cassette disassembly, that is OK.
When recovering a disaster damaged reel-to-reel tape, a good quality tape pack wind will minimize recovery efforts. In this case, cleaning the outer surfaces of the tape pack and the reel should be sufficient to recover the tapes. Use of a winder-cleane r will only be necessary if the debris has infiltrated between the tape windings. This can happen if the tape pack was loose, the tape had poor wind quality (several popped strands), or if the contamination was invasive, such as is the case with fungus a nd mold.
Generally, it is not necessary to open a cassette tape unless the disaster has resulted in contamination of the inside of the cassette. Otherwise, cleaning of the outside of the cassette should suffice. If the cassette has been exposed to water for an e xtended period of time, it may be necessary to open the cassette and check the condition of the cassette spindles and springs. These should be replaced if they show evidence of corrosion or rusting.
Prioritization of tape recovery efforts: In terms of tape backings, paper backed tapes should have precedence over acetate backed tapes, and acetate backed tapes should have precedence over PET backed tapes. The more corrosive reduced metal based tapes (MP and ME), which are more susceptible to corrosion, should receive attention before oxide based tapes which are much more stable in adverse environments. The remainder of the chart should be self explanatory.
Here is a photograph showing a flight recorder from a crashed F-16 aircraft. The damaged 8mm tape can be seen within the recorder.
Recovery of the video information prior to the crash was requested by the Crash Investigation Board. Information from the Heads Up Display and the Left Multifunction Display was to be used to determine the probable cause of the crash.
The tape was sent to the Kodak Recording Systems Analysis Laboratory for recovery. Individuals involved with the recovery process included--Robert Bachner, Timothy M. Enders, Daniel J. Sillick, James A. Craven, and David R. Kaiser.
For a detailed description of the efforts used to recover video images from a flight recorder from an F-16 jet which crashed (Slides 37-39), refer to "Kodak experts recover critical video images" and "Video Image Recovery from Damaged 8mm Recorders."
Recovery of the video images proved to be a formidable, but not impossible task.
Large sections of tape were spliced and re-spooled into a good tape cassette. Sections of tape that were appreciably wrinkled were thermally reconditioned to flatten them prior to re-spooling. Even small pieces of tape were painstakingly spliced togethe r.
Sections of tape less than 3 inches in length did not contain a full video track. In this case, image fragment had to be collected and were later reconstructed into a full image.
Here is an image of the Heads Up Display recovered from the 8mm video tape. Recovery of images of this type provided enough information to determine the cause of the crash.
In recovering damaged tapes it is important to avoid damaging the edge of the tapes. As most tapes are edge guided through the recorder, this can result in mistracking. High temperatures should be avoided as this will increase tape pack tension and may cause the tape backing to stretch. Low temperatures and tape freezing should be avoided as this can loosen tape packs allowing debris infiltration between tape pack windings. High and low temperatures can also result in print through and lubricant migrat ion to the tape surface, respectively. When cleaning tapes it is very important to remove all dust and debris, otherwise it can get between the tape and the tape head on playback causing dropouts.
In contrast, when recovering optical disk materials, it is very important not to scratch either side of the disk. A scratch on the substrate side of a CD-ROM (the shiny side) can result in a permanent misread of information. A scratch on the protective coating side (label side) can expose the data layer to the elements accelerating the rate of disk degradation. Dust and debris remaining on a CD-ROM after a recovery effort can also result in a misread of the disk. Cleaning the debris from the disk shou ld correct the temporary misread. In some instances, extremes in temperature can cause microscopic cracks in the data layer on an M-O disk.
Optical disk recovery efforts are similar to those used for magnetic tapes. However, with optical disks it is extremely important to avoid scratching the surfaces of the disk during the cleaning process. If the soil being removed is sandy or gritty, it is important that one does not rub these abrasives into the surface of the disk.
When wiping debris from an optical disk, it is important to wipe from the center of the disk to the edge (wiping radially). DO NOT wipe around the disk in a circular motion (wiping tangentially). Disk tracks on an optical disk are either laid out as con centric circles or as one continuous spiral. If one wipes around the disk in a circular motion, any scratches that may be produced will run along the disk tracks and may obscure large portions of a track which may not be recovered using the build in erro r correction code (ECC). If a scratch is accidentally produced when wiping radially across the data track, less of the track will be obscured locally so that there is a better chance that the ECC scheme can recover the missing portion of the data.
In conclusion, the best way to recover from disasters is to prevent them from occurring.
Proper care and handling of the tape can increase the service life of the tape. Storing at cool temperatures and low humidities slows natural decomposition processes and reduces the effects of binder hydrolysis. It is best to store tapes and optical dis ks at temperatures below 72 F and humidities below 50% RH. Storage temperatures and humidities should remain stable to reduce stretching and shrinking of the tape pack. A high quality tape pack should be maintained to (1) reduce non-uniform deformation of the tape backing, and (2) minimize the clean-up effort required after a disaster. Refer to "Magnetic Tape Storage and Handling: A Guide for Libraries and Archives" for more details on proper storage and handling.
Disasters should be anticipated and prevented before they are allowed to occur. If a flood or hurricane is imminent, and you have tapes stored in a basement, it would be advisable to move them to upper level floors away from exterior walls.
When salvaging magnetic media damaged in a disaster, (1) avoid extremes in heat and cold to avoid loosening or over stressing the tape pack, and (2) avoid damaging the edge of the tape. Wet tapes do not need to be frozen to protect them from further harm (freezing can actually cause more damage). In fact, tapes can remain wet while more vulnerable items in the collection are dealt with first, such as books and paper backed photographs. Heat drying methods should be avoided because of the increased stre sses high temperatures cause in the tape pack.
When recovering damaged magnetic tape media, in general, deal with them as you would microfilm or motion picture film. Magnetic tape can be thought of as a high quality paint coating on a plastic film. Do not treat magnetic tape like paper, unless the m agnetic tape is very old and uses a paper backing.
When recovering optical disks it is very important to avoid scratching either side of the disk.
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