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Making the Nation Safer: The Role of Science and Technology in Countering Terrorism
Improved Filters, Absorbents, Scrubbers, and Membranes for Chemical Decontamination and Restoration of Function
In most cases, the impact of a chemical attack would not be limited to the harm done at the time of the attack. Afterward, it could take a long time to decontaminate the site, as well as to restore public confidence. Restoring the Hart Senate Office Building after it was contaminated by anthrax exemplified the difficulty of decontamination in the wake of a biological attack. Comparable efforts following a chemical attack would be different, but not necessarily easier. Contamination by a volatile agent (e.g., sarin) presents the problem of removing a toxic vapor without releasing it into the outside environment. Contamination with a persistent agent (e.g., VX) poses an additional concern—much of the agent may deposit on surfaces, and the chemicals used in decontamination, such as hypochlorite solution, are generally incompatible with electronic equipment and paper. Regardless of the type of contamination, however, persuading the occupants of the building to reenter and go back to work will require credible technical evidence that it is safe to do so.
Research is needed to identify more effective technologies for removal of contaminants from different media (air, water, and solid surfaces) and to quantify their effectiveness so that appropriate decontamination measures can be developed. These technologies are likely to be specific for the contaminants involved and for the media in which they are dispersed. Contaminants in air or water—chemical, biological, or nuclear—may be present as aerosols (particles of solid or liquid) in air or as particles in water, or they may be homogeneously dispersed, as gaseous contaminants in air or dissolved contaminants in water.
Particles may be removed by filtration, with the specific technology depending on particle size (Accomazzo et al., 1988; Ensor, 1988). Several filtration technologies are available: micro-, ultra-, and nanofiltration membranes for treating contaminated water and HEPA (high-efficiency particulate air) filtration for contaminated air. Improved high-efficiency and low-pressure-drop filter systems could be useful in rapidly treating large volumes of particle-contaminated water or air.
Homogeneously dispersed contaminants may be removed by absorption,6 adsorption,7 chemical reaction/neutralization, or selective membrane filtration (Ho and Sirkar, 1992; Majumdar and Sirkar, 1988; Prasad and Sirkar, 1987; Way et al., 1982). Absorbers and filters can be used both to prevent toxic chemicals
Absorption is a process in which a material extracts one or more substances present in a mixture of gases or liquids, accompanied by changes in the material’s physical or chemical properties.
Adsorption involves surface adherence, in which a material extracts one or more substances present in a mixture of gases or liquids, unaccompanied by changes in its physical or chemical properties. Commercial adsorbent materials have enormous internal surface areas, typically several hundred square meters per gram.