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REQUIREMENTS AND CONSIDERATIONS FOR CHEMICAL DEMILITARIZATION TECHNOLOGIES 86 and if the cooling is slow enough to allow the reaction to take place. The same is true for all bulk liquid agent destruction processes that use high temperatures and then provide for cool down of the reaction products to ambient temperatures. A measure of the significance of these considerations may be gained by reviewing the JACADS operating experience. Although the level of production inside the current JACADS furnaces and related afterburners is not known, the immediately downstream pollution abatement systems axe designed to minimize subsequent chlorinated dioxin production conditions by using a water quench to rapidly cool the gases to about 60°C and then remove both HCl and Cl2 by contact with a sodium carbonate solution. Analysis of the exhaust gases from the JACADS systems has shown little evidence of significant residual chlorinated dioxins. However, traces of chlorinated dioxins were found in the stack emissions when projectiles containing high residuals of HD were heat treated in the metal parts furnace. Under these conditions the quantity of chlorinated dioxins varied from 0 to 0.16 ng/m 3, more than an order of magnitude less than emitted from municipal incinerators (MITRE Corporation, 1993). The low-temperature chemical and biological processes axe not expected to form chlorinated dioxins because the recombination temperature conditions will never exist. Subsequent filtering for particulate removal or storage of effluent gases at approximately 120°F, such as would exist after passing through a water-scrubbing pollution abatement system, is not expected to form additional chlorinated dioxins. In fact, the use of activated charcoal filters would be an effective method for further removal of chlorinated dioxins. While the production of chlorinated dioxins should be minimized, and subsequent removal methods should be provided, periodic monitoring for the their presence would also be prudent. MONITORING The detection of chemical warfare agents at extremely low concentrations is difficult in practice for several reasons (NRC, 1993): ⢠There axe several agents in the U.S. stockpile, GB, VX, and HD (mustard), with different characteristics. ⢠All axe complex organic compounds without an identifying characteristic that allows easy and rapid identification. ⢠The agents may be masked by, as well as mistaken for, other organic compounds that happen to be present in higher concentrations.
REQUIREMENTS AND CONSIDERATIONS FOR CHEMICAL DEMILITARIZATION TECHNOLOGIES 87 In the current Army method of analysis, air samples are collected by withdrawing a small air stream from the process stream, the atmosphere, or air adjacent to potentially contaminated material. This air stream is then passed through a sample collection robe, where organic components are deposited on an absorbent medium. For quick analysis of limited sensitivity, sample collection time may last only a few minutes. For the detection of smaller quantifies of agent, the amount of sample collected must be larger, and the collection time may be several hours. This sample is then desorbed into a gas chromatograph with a flame photometric detector. The minimum level of detection now used for all agents is very small, about 20 percent of the maximum allowable concentration for uncontrolled access (Table 4-1). Although the maximum allowable concentration of agent is 3 ng/m3, the minimum detectable amount for several hours of collection time is about 0.6 ng/m 3. As noted above, for GB this is equivalent to about 2.6 Ã 1012 molecules/m3. The Army requirement to detect these very small quantities (Table 4-1) leads to many false positives, more than found with less sensitive measures, bemuse the instrumentation detects other similar organic compounds that emerge from the chromatographic column at the same time as agent. Especially for future operations in the continental United States, false alarms should be minimized because of the delays for retesting and other associated problems. The storage of gas emissions will allow time for the analysis required for certification (see Chapter 5). However, improved test reliability as well as sensitivity is highly desirable. The NRC recently discussed with the Army the conduct of farther R&D on the use of agent- specific mass spectrometry, which should decrease both false positives and analysis time (NRC, 1993). The existing gaseous-waste monitoring equipment was developed for use on well-oxidized gases saturated with water vapor. Selection of any alternative technology would require further development of early monitoring equipment if other components, such as incompletely oxidized hydrocarbons or sulfur compounds, are present to any significant degree. In addition, any alternative technology will need to have its own monitoring capability for process control, the nature of which must match the chemistry and physics of the specific internal process steps needing control. Although these are readily available for many measurements, a review of the specific requirements and equipment availability should be made before any selection is finalized. Any requirement for invention of monitoring equipment would involve a high risk.
