reduced inventories of hazardous chemicals stored at manufacturing sites. Innovations involving less-toxic starting materials, intermediates, products, and by-products have lowered intrinsic dangers to workers, the public, and the environment and at the same time reduced the availability of materials that might fall into the wrong hands. Over-the-fence manufacturing—whereby the supplier builds a plant immediately adjacent to the customer’s plant, or even on the customer’s site—provides a reliable source of materials while minimizing transport and storage. Probably the most significant change has been the ability to monitor and control reactions on a real-time basis; real-time control reduces the chances for accidental or intentional releases. These trends show that many technical changes intended to increase efficiency, reduce environmental impacts, and improve safety can also reduce the threat of terrorist attacks.

Despite these advances, the volume of toxic materials in production, transport, and storage is still enormous, and as a result there are still many hard-to-protect targets. Chemicals could be released from industrial facilities or pipelines, for example, using explosive charges or simply by cutting pipes or opening valves. Under some meteorological conditions, release from production and storage facilities could permit a toxic plume to pass over heavily populated areas. Transportation systems (e.g., railroad tank cars, ships and barges, and trucks) allow rapid transport of hazardous chemicals, and terrorists could take advantage of these vehicles’ frequent proximity to potential targets (e.g., trains that travel under cities or barges located in harbors) (see also Chapters 7 and 8).

Thus new technologies or further incentives to reduce the amount of toxic materials being moved around the country would be very useful. Taxes placed on transport and storage of highly toxic chemicals, combined with public-private research partnerships, perhaps managed by EPA, could be used to encourage the development of new approaches to on-site and just-in-time production. For example, new process technologies to allow small-scale production of chlorine at water-treatment plants could greatly reduce shipments of this hazardous material.

Explosives and Flammable Agents

Explosives, having many legitimate purposes and being relatively accessible, pose a significant terrorist threat (NRC, 1998). They can be used in large quantities to produce mass destruction, as in the attack on the Murrah Federal Building in Oklahoma City, and in smaller quantities to destroy sensitive or symbolic targets such as airplanes, bridges, or key components of critical infrastructures (e.g., telecommunications networks, electric-power grids, and water supplies). Legally mandated controls apply to industrial and civil engineering explosives, but the quantities in use are large and the control mechanisms imperfect. More important, as the Oklahoma City attack shows, very powerful explosives can be readily assembled from such otherwise innocuous ingredients as agricultural chemicals and fuel oil.

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