This article describes measures taken to protect valuable documents. Helium is used to surround the document. It is chemically inert, will not support organic life and has a relatively high thermal conductivity that facilitates the detection of air leakage. Helium's relative humidity at room temperature ( 25 to 30 percent ) is the correct range for durability of the collagen protein in the parchment documents. An airtight, transparent tempered plate glass enclosure requires a sealing process with minimum heat transference. A thermal conductivity type gas analyzer detects leaks. The circuit consists of measuring cells sealed within the enclosure with Kovar tubes extending through and connecting to external cells. Comparison of the resistance with temperature of the platinum wire in each of the cells is measured by a microammeter. Pure cellulose backing paper meets requirements for purity and chemical stability and acts as a compensating reservoir for moisture in case of rapid temperature changes. A laminated glass filter with a plastic interlayer of yellow cellulose acetate is placed over the enclosure. This eliminates harmful ultra-violet, visible blue and violet light. -- CCI=IC