ANN ARBOR—More than 10,000 master microfilm negatives belonging to the University of Michigan Library are stored 220 feet below ground in an old limestone mine in western Pennsylvania. ” In our archival storage vault there,” says Shannon O’Dell, preservation services assistant at U-M, ” the environment is maintained at a constant 68 degrees and 20-30 percent relative humidity.”

This high-tech, high security, state-of-the-art environmental storage facility (which prefers to remain nameless) is used by more than 500 other libraries, national companies, banks, and the film industry.

” After WWII the Federal government directed that industries vital to the national defense secure their records,” says Carla Montori, head of U-M Library‘s Preservation Division. ” At that time U.S. Steel owned the lease to the caves from which they mined limestone. The records manager for the company got the bright idea of going commercial, and bought the lease for an unused portion of the cave system. U.S. Steel denied him access through their entrance, so he had to construct his own film in his cave.”

Now the master negative for every microfilm reel ever made by the U-M Library Preservation Microfilming Lab, both for its ongoing in-house Brittle Books Replacement program and for all grant-funded preservation reformatting, is stored at the Pennsylvania facility for safekeeping, says Ann Thomas, head of preservation support services.

” A printing negative used for duplication as requested through Interlibrary Loan, is stored within the Library’s Preservation Division space in the Buhr Building and a positive copy for Library patron use is on site, available in Microform Services at the Hatcher Gruaduate Library,” says Thomas.

The Pennsylvania archival storage facility was carefully selected in the early 1980s by the Research Libraries Group of which U-M Library is a member. As an RLG member, U-M was eligible to sub-lease microfilm storage space within a vault rented by RLG. ” Each of our reels was assigned a cabinets,” says Thomas. ” RLG grant-produced reels, although accessible to us if needed, are owned by RLG and remain in their vault. Those produced for non-RLG grants and for our in-house replacement program are owned by us.”

Two years ago, these U-M owned reels were moved, at U-M’s request and expense, into an archival storage vault at the Pennsylvania facility rented by the Committee on Institutional Cooperation (CIC), another consortium of large academic libraries of which U-M’s Library is a member. In the CIC vault, U-M’s reels are stored in archival storage boxes on shelves, each reel having a designated ” box/shelf” number by which it can be retrieved if ever needed.

Secure in part of 1.2 million square feet of developed storage space in caves and/or mines more than 200 feet below 133 acres of western Pennsylvania and protected by a three ton steel gate and armed guards on duty 24 hours a day, U-M’s microfilm holdings are as safe as any vital defense documents.