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13 soon extend as much as tens of miles downwind before grad- way of dispersing them. If terrorists were able to obtain or ually falling below the concentrations of concern. Heavy manufacture chemical munitions, they could cause a more vapor clouds also tend to run into depressions, ditches, devastating effect. drains, and basements of buildings (if released in an urban The use of crop duster planes to disperse chemical area). They can persist there for several hours if the wind weapons agents is considered to be possible, but very un- speed is low or if enclosed spaces are not well ventilated. likely. Without substantial reconfiguration, crop-dusters can This can be dangerous for unwary members of the public and only release liquid droplets that are much larger than can be emergency rescue personnel. taken into the lungs, thus only agents that cause injury by Computer models such as RMP*Comp (Risk Manage- contact could be effective. Blister agents and the nerve ment Plan offsite consequence analysis software) (EPA, agent, VX, have been identified as potentially able to be ef- 2004) are used to predict the area over which a toxic cloud fectively dispersed with a crop duster. Difficulties would in- may spread. These models generally are conservative, so the clude preventing leakage (for VX in particular, even distance over which a cloud would cause harmful effects in minimal exposure would kill the pilot before leaving the the field would often be less than predicted by the models. ground) and infiltrating both a crop duster company and one Atmospheric conditions such as inversions may have a sub- of the traditionally separate, specialized companies that load stantial effect on the dispersion of toxic gases. An inversion chemicals into crop dusters. is considered the optimum condition for an open-air chemi- cal weapons release. Inversion occurs when the ground is cooler than the air, and temperatures increase further from 2.1.3 Threats and the Transportation System the ground. Under these conditions, there is little air turbu- lence and wind speeds are low, thereby reducing the rate of The transportation system has particular vulnerabilities dispersion of a chemical release. The 1984 release of methyl with respect to chemical threats and, as discussed below, is isocyanate (a choking agent) at a pesticide factory in Bhopal, likely to be involved in actions to minimize the consequences India, occurred during an inversion, which had slow but of a chemical event. steady winds. The toxic cloud moved to a densely populated area where it killed more than 2,500 people and caused tens of thousands of permanent respiratory injuries. Transportation System Vulnerabilities Similar to gases, aerosols and fine particles from chemi- cal weapons may be dispersed by natural wind and wind A chemical release event that occurs near or in any generated from traffic. In contrast to gases, particles dis- transportation mode can contaminate the roadway or track persed by wind eventually will be deposited onto surfaces. on which vehicles travel, transportation vehicles, passen- The atmospheric dispersion of small particles and aerosols gers, and cargo passing through the contaminated area. is affected by many factors, such as energy in the dispersion Factors that make a transportation mode more vulnerable (i.e., fire, heat, or explosion), height of release, presence to sustained toxic concentrations during a chemical event of obstructions (e.g., buildings, hills, and mountains), and include the presence of enclosed spaces, the likelihood of weather conditions (e.g., wind speed and direction, temper- persistent contamination, and the ease (or difficulty) of de- ature, humidity, rain, and cloud cover). The most important contamination. These factors and other vulnerability fac- factors are wind speed, wind direction, energy and height of tors are summarized in Table 2-6 for each transportation release, and the presence of obstructing structures or natural mode. features. Re-suspension of particles with traffic-generated Enclosed spaces such as tunnels and, to a lesser extent, wind is possible but most of the chemical agents are gases road and track surrounded by tall buildings, may more read- or aerosols for which re-suspension is not generally an issue. ily retain toxic vapors, aerosols, and particles than open Spilled liquid chemicals will form a slowly evaporating spaces. Gaseous and aerosol chemicals may enter vehicles pool on the ground. The rate of evaporation is affected by and vessels with air, and in all transportation vehicles, may factors such as the boiling point of the liquid, ambient tem- be more readily retained in passenger and cargo compart- perature, the area over which the liquid spreads, and the wind ments than in the open air. Factors that reduce the ability speed. The Aum Shinrikyo cult used an evaporating liquid to for quick dilution of toxic gases or aerosols (e.g., enclosed release a few liters of the nerve agent, sarin, in commuter spaces) allow people and cargo to receive larger doses, trains on three Tokyo subway lines in 1995. The sarin was thereby increasing health effects. Among the largest public concealed in lunch bags and soft-drink containers, and placed populations at risk in enclosed spaces are in transit under- on subway train floors. The containers were then punctured ground stations or terminals, airport terminals, large civil with umbrellas, spilling sarin on the floor as the perpetrators aircraft, and passenger cruise ships. Enclosed spaces with left the trains (Ohbu et al., 1997). The incident resulted in HVAC systems have increased exposure risks caused by 12 deaths and about 1,000 injuries. Pouring liquid nerve and continued circulation of toxic chemicals in the form of gases, blister agents on the ground or floor is a relatively inefficient aerosols, or fine particles. Food and water cargo present

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14 TABLE 2-6 Vulnerabilities to Extended Chemical Exposure for Each Transportation Mode (Note: High more vulnerable (higher risk), Medium medium vulnerability, Low less vulnerable (lower risk)) Chemical Highway Rail Transit Aviation Maritime Vulnerability Enclosed space Tunnels Tunnels, Tunnels Aircraft Cruise ships Passenger Stations Stations/terminals Terminals Terminals compartments Passenger Passenger compartments compartments Persistent High for High for stations, High High for High for cruise contamination a passenger passenger trains aircraft and ships, and vehicles airports terminals Ease of Moderate Moderate Moderate Moderate Moderate decontamination a HVAC spread None Within Within passenger Within Within cruise contamination passenger car compartments, airports and ship and or station terminals aircraft terminals Drinking water None Passenger Passenger drinking Passenger Passenger contamination drinking water water drinking water drinking water Agricultural cargo Yes Yes No Slight Yes contamination Able to contaminate Transfer points Transfer points Transfer points Airport Dock other modes terminal a: Persistent contamination and decontamination are only issues when a persistent chemical is released (i.e., some chemical weapons agents). concerns as both a primary target for contamination and as trapped or injured people. For rapid response in the event a transportation system cargo that has passed through a conta- chemical weapons agent is detected in association with an minated area. explosion, emergency response plans may specify an imme- Toxic particles and, to a lesser extent, aerosols, can be diate, conservative radius surrounding the explosion site for re-suspended or evaporated more quickly by air currents gen- evacuation. These boundaries may be adjusted after a more erated by passing traffic. In the contaminated area, highway complete chemical survey. A difficult and probably contro- vehicles and rail or subway cars in particular can expand the versial aspect of determining transportation response goals contaminated area. Contaminant spread by traffic could also will be in establishing the physical boundaries of isolation be an issue in ports, docks, canals, and rivers. The open sea, areas. Transportation officials are unlikely to have primary however, is not susceptible to significant chemical contami- responsibility for these decisions and probably will be fol- nation from passing ships because its enormous volume lowing instructions from the emergency operations center. would dilute any toxins to an insignificant concentration. In the event of a persistent chemical release, successfully Intersecting modes of transportation can result in cross- routing all potentially exposed traffic to decontamination contaminating one transportation mode from another. Primary areas depends on the time it takes to recognize that a chemi- mode intersections include rail crossings, stations, airports, cal weapons agent has been released. Symptoms from most ports and docks, and mass transit lines and/or stations. This chemical agents appear within minutes, but in the case of de- physical proximity can result in contamination spreading from layed detection of a release, effort may be needed to identify, one transportation mode to another. decontaminate, and provide medical assistance to contami- nated travelers, vehicles, and cargo after they have left the area of initial contamination. Consequence Minimization of a Chemical Event In some outdoor release cases (e.g., blister agent or VX), it may be safer for people to remain inside buildings (i.e., shel- The first response in the event of a chemical release that ter-in-place) than to evacuate. In other cases, such a distant re- contaminates transportation pathways would be to close the lease of a large amount of a choking agent that may travel to affected paths until a non-persistent chemical is diluted a populated area, population evacuations may be necessary. or chemically broken down or until a persistent chemical In these cases, transportation paths may be re-routed to expe- is otherwise removed. Depending on the released agent's dite one-way travel. If the people, vehicles, and cargo from persistence, potentially contaminated people, vehicles, and evacuated areas have the possibility of being contaminated associated cargo may be routed to isolation and decontami- with a persistent chemical, isolation and decontamination nation areas or directly to medical assistance. Transportation stops would be established along evacuation routes. Essen- would need to be provided for first responders to assist tially all modes of transportation may assist in population