Over the past several decades, ethylene oxide gained such wide acceptance in the library and archival preservation world, that in spite of the risks its usage presents, it has not been easy to replace with another fumigant. This biocide has an unparalleled track record of effectiveness against insects as well as microorganisms and also the absence of any significant ill effects on archival as well as museum collections themselves, although it is not entirely unblemished (Green, 1987).
A little over ten years ago, several public and private repositories routinely fumigated materials that were even remotely suspected of mold or insect infestation. For example, the U.S. National Archives subjected all incoming records to ethylene oxide fumigation as a precautionary measure for several decades. Now we know that ethylene oxide can be deadly not just for mold and insects, but also for us if it is not used within accepted limits (OSHA, 1982-5, Lewin, 1986). Chronic exposure to ethylene oxide can increase the risk of leukemia, brain tumors and other cancers; it can cause chromosome damage and may also affect the reproductive system.
It is now generally accepted that several natural, as well as synthetic polymeric materials tend to retain significant amounts of residual ethylene oxide subsequent to a fumigation treatment. The residual ethylene oxide is then gradually released into the environment over an extended period of time. Such offgassing phenomena are of particular concern since they extend the population that is routinely exposed beyond the limited numbers of workers who operate the sterilization/fumigation chambers, and who - one would expect - would be equipped to deal with the risk in an appropriate manner. In the case of fumigated library materials, this risk can be extended to unsuspecting and unprepared curators and other personnel who routinely service the fumigated materials. Researchers and readers exposed to such materials are also put at risk, although to an appreciably smaller extent since their exposure would be expected to be occasional, or short-term.
In 1984, the U.S. Occupational Safety and Health Agency (OSHA) specified a standard for occupational exposure to ethylene oxide, which among other provisions lowered the Permissible Exposure Level (PEL) from 50 ppm to 1 ppm. (OSHA, 1984). In that document, OSHA reserved judgment on the need for and the appropriateness of a short-term exposure limit. Following scientific peer review and public comment on the issue of a short-term exposure limit, OSHA published its determination that the available evidence did not support the imposition of such a limit (OSHA, 1985).
The present work was undertaken to comprehend the capability of different library materials to offgas ethylene oxide. The objective was to obtain some understanding of the extent of aeration that different materials require after fumigation with ethylene oxide. Such knowledge would allow for better planning and control of the fumigation process and aid in the management of any risk that ethylene oxide offgassing may present to library personnel and users. It is not the intent of this work to suggest that such risk is unmanageable. Moreover, the rates of desorption of residual ethylene oxide observed in this work have no relevance on an absolute basis since desorption can be accelerated appreciably by raising the temperature and relative humidity levels of the air. The desorption rates observed here are useful only for the purpose of comparing these rates on a relative basis for different materials investigated in this work.
In 1982, OSHA issued an Advance Notice of Proposed Rule-making stating that the then-current occupational safety and health standard for ethylene oxide -50 ppm measured as an 8-hour time-weighted average (TWA) -- may be inadequate to protect exposed workers from significant risk (OSHA, 1982). At this point, it became clear to us that it was important to institute measurement of ethylene oxide concentration levels during the fumigation process. We began to monitor ethylene oxide by withdrawing gas samples from inside the fumigation chamber after successive air-changes before opening it up. The very first time that we started this practice, we were taken aback that after three evacuation-air change cycles, where we would have normally opened up the chamber, we still had an ethylene oxide concentration of several hundred parts per million within the chamber.
The materials being exposed at that time consisted mainly of wood, paper and interestingly enough -- several bags of horse hair, which came not from the Library's collections but from the U.S. National Park Service. We had to exchange the air in the chamber as many as 28 times over several days before we could bring the ethylene oxide concentration to under 1 ppm. We speculated about the wood or horse hair being responsible for the strong retention of residual ethylene oxide. Clearly, we needed to know a lot more about the capability of different materials to retain residual ethylene oxide so as to exclude them or treat them separately. Hence the present series of experiments in which we simulated in the laboratory the operational conditions in our larger 500 cu. ft. fumigation chamber.