Volatile Organic Compounds (VOCs) – The Scent of Our Collections and the Things That Hold Them

This is a guest post written by Dr. Eric Monroe, Head of the Scientific Laboratory Section of the Preservation Research and Testing Division. One of his research interests involves examining the impact and consequences of volatile compounds and odors in the Library.  

The presence of odors throughout the Library of Congress is hardly a surprise to anyone. Many people find the smell of ‘old books’ is both distinctive and familiar, but the extent of odors at the Library can extend far beyond those from our paper collections. Odors are caused by the presence of volatile organic compounds (VOCs) in the air. Often, these compounds are thought of as being innocuous or as a health and safety concern. However, these compounds can also present risks to the long term preservation of the collections, even when they pose no health risk to people.

In the Library, VOCs can emit from almost everywhere including from aging collections, visitors (clothing, perfume, personal care products, etc.), the outside environment, as well as materials used in the construction of storage areas, housing materials for collection items, and exhibition cases. We will save discussion of the compounds coming directly from collections for a later blog and focus here on how we look at the materials in spaces that are close to collections, and how they may present a risk to collections.

One test method that is broadly used in museums and libraries to detect the presence of harmful emissions is the Oddy test. This test was developed in the 1970s and involves exposing test metals (typically lead, silver, and copper) to volatile compounds from a test material within a sealed jar under elevated temperature and humidity. After 28 days of exposure, the metals are examined for signs of corrosion, tarnishing, and/or deposition. While broadly used, this test presents certain limitations in regard to reproducibility, interpretation, and required test duration. Additionally, we can’t identify the ‘bad actor’ and it takes a month to get results. That’s a long time when we don’t want to cause harm to our collections.

While PRTD still regularly performs Oddy tests on materials proposed for storage space and exhibition construction, we have been exploring the use of a methodology faster and more accurate for the last several years. We have adapted a testing method typically used in the automotive industry to examine the off gassing of materials used in the cabin of automobiles and identify not only what compounds are coming off of the plastics, fabrics, etc. in the car but also how much of each compound will be emitted from the material. (It turns out that new car smell is not necessarily good for drivers and manufacturers are particularly keen to reduce the deposition of films on the inside of the windshield and windows.)

This method is formally known as direct thermal desorption gas chromatography mass spectrometry (DTD-GCMS). The technique places a small amount of a material to be tested into a glass tube and it is heated in a small oven on top of the GCMS instrument. While heated, the volatile compounds are extracted from the sample and then separated and detected/identified by the GCMS.

We have applied this testing protocol to construction materials for new storage facility construction, vault renovations, and multiple exhibition cases and have identified several materials that would present significant risks to collections during storage or public exhibition. Ongoing work to cross-reference Oddy and volatiles results is leading to a better understanding of compounds that pose a risk to collections. In most cases, the results from the volatiles testing can point to the cause of Oddy test failures. For instance, multiple volatile compounds were detected from a proposed flooring material that were predicted to cause issues in the Oddy test. This was definitely the case as a large growth from the lead test coupon was observed, an event we never want to see happen to our collections. In other instances, the presence of a sulfur-containing compound (or several) being detected from proposed gasket and board materials for exhibition cases within hours rather than requiring several weeks of testing as needed for the Oddy test. Sulfur compounds have been shown to damage collections containing silver via rapid tarnishing and present a significant risk to collections. While none of the compounds detected in either of these examples would pose a health or safety hazard to personnel, this could not be said for potential risk to collections.

We have further adapted this new test method after the installation of new building materials, as a double check to ensure no volatile compounds are present that we would not expect. This portable system uses a sorbent material that captures volatile organic as we collect an air sample from the room or exhibition case. This process was, for instance, used with the Gutenberg Bible case prior to the initial installation of the Bible in the new case.

As you can see, we have been adapting methods from across different disciplines to advance our preservation techniques, since this can be helpful for cultural heritage to move into new methods of analysis.  We use a wide array of methods and protocols in order to address myriad of questions from across the different collection materials, and you will hear more about others of these in the future.