The use of thermal desorption in monitoring for the chemical weapons demilitarization program

Under international treaty, the United States and Russia are disposing of their aging stockpile of chemical weapons. Incineration and chemical neutralization are options for sites in the United States, although Russia prefers the latter. The storage and disposal of bulk and chemical agents and weapons involve unique hazards of handling extremely toxic materials. There are three major areas of concern--the storage stockpile, the disposal area, and the discovery and destruction of "found" material not considered part of the stockpile. Methods have been developed to detect the presence of chemical agents in the air, and these are used to help assure worker protection and the safety of the local population. Exposure limits for all chemical agents are low, sometimes nanograms per cubic meter for worker control limits and picograms per cubic meter for general population limits. There are three types of monitoring used in the USA: alarm, confirmation, and historical. Alarm monitors are required to give relatively immediate real-time responses to agent leaks. They are simple to operate and rugged, and provide an alarm in near real-time (generally a few minutes). Alarm monitors for the demilitarization program are based on sorbent pre-concentration followed by thermal desorption and simple gas chromatography. Alarms may need to be confirmed by another method, such as sample tubes collocated with the alarm monitor and analyzed in a laboratory by more sophisticated chromatography. Sample tubes are also used for historical perimeter monitoring, with sample periods typically of 12 h. The most common detector is the flame photometric detector, in sulfur or phosphorous mode, although others, such as mass-selective detectors, also have been used. All agents have specific problems with collection, chromatography and detection. Monitoring is not made easier by interferences from pesticide spraying, busy roadways or military firing ranges. Exposure limits drive the requirements for analytical sensitivity. Lowering limits adds additional difficulties to the monitoring efforts. The various monitoring methods and the role they play in ensuring worker and general population safety are discussed.