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OCR for page 11
11 holding of run-off water with more treatment until accept- Quantity and Persistence able levels of both the initial contaminant and any added de- contaminants (i.e., chlorine and soap) are reached. The quantity of a chemical released and the chemical type and toxicity determine the potential human health effects. The quantity and persistence of the released chemical deter- 2.1.2 Emergency Response mine the duration of the human health risk. An upper range Information Needs estimate of the quantity of a chemical release from an indus- trial storage or transport container can be determined easily Regardless of the cause of a chemical release, from an on the basis of container size and can assist in developing a emergency response perspective, the primary considerations conservative estimate of the area that may receive concen- for response management are the chemical type and toxicity, trations of concern. The larger volumes of chemicals in trans- quantity and persistence, exposure route; and dispersion and port are in railcars, with amounts up to 90 tons per car, and population density in the area at risk. These factors and their on inland and coastal barges in amounts up to 2,500 tons per interrelationship are discussed below. Table 2-3 delineates barge. These containers may be particularly attractive from a some of the information needed in a chemical event to decide terrorist perspective because of the possibility of very the appropriateness of transportation goals for isolation, shel- quickly releasing large quantities of a toxic chemical. Toxic ter-in-place, evacuation, and checkpoint establishment. gases (transported as both gases and as liquids under pres- sure) are generally not very persistent, so typically present Chemical Type and Toxicity only a short-term threat. Estimating the release quantity and associated area with Chemical type and toxicity are key factors in assessing the concentrations of concern may be more problematic from a threat posed to human health, thus is important for determin- chemical weapons release, particularly if there is a delay be- ing appropriate protective wear for first-responders and tween exposure and observable symptoms. Particularly clean-up personnel, and population risks. The health risks to among blister and nerve agents, the persistence of chemical responders and the general population are also affected by toxicity after release varies greatly (i.e., from minutes to the contaminant concentration (derived for the initial quan- weeks). The identification of a chemical weapons release tity and area of dispersion) and the exposure route. In popu- agent needs to be confirmed with laboratory tests to estimate lated areas, the general type of a released chemical can often confidently its persistence and the protective wear needed be assessed within minutes of release because of the rapid during clean up. onset of symptoms. Most industrial transport chemicals are choking agents or asphyxiants. In non-industrial events, mul- tiple agents may be released, and a more common agent, such Exposure Route as tear gas, initially may mask the presence of another agent, Possible exposure routes are determined by whether the such as the blister agent mustard gas, for which symptoms chemical is a gas, liquid, or solid. If it is one of the latter two other than those similar to tear gas may be delayed for several forms, aerosol or particle size and evaporation rate must also hours. be considered. Inhalation is the primary exposure route of concern for choking agents and for some nerve agents TABLE 2-3 Determination of Chemical (e.g., sarin). In a severe release, inhalation may also be an im- Event Emergency Response portant exposure path for some blister agents. The time re- Chemical Event quired for an agent suspended in air to be diluted, and for par- Information Needed to Determine Appropriate ticles and aerosols to settle to the ground and evaporate, Emergency Response determines how long inhalation is a concern. The size of the Estimated population exposed to levels of concern as particles is critical in that if the particles are too large, they determined from: quickly fall to the ground and no longer pose a threat through Affected area information (see below) Population data the inhalation exposure route. Table 2-4 provides estimates Estimated affected area as determined from: Quantity and toxicity of material Release parameters (density, temperature, TABLE 2-4 Particle Size and momentum, etc.) Sedimentation Rate in Stagnant Air Location of release Wind direction and speed Particle Diameter Time to Fall 100 Ft. Topography, urban or rural environment 100 microns 2 minutes Levels of concern (i.e., toxicity) 10 microns 3 hours Possible exposure pathways as determined from: 3 microns 30 hours Chemical identity 1 micron 240 hours Physical form (gas, liquid, solid) 0.5 microns 820 hours
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12 of how long it takes various particle sizes to settle to the water within the transportation system is possible, but prob- ground when there are no wind currents. ably would not be a very large event in terms of injuries or The smaller the particle, the further it may travel within the casualties. respiratory tract. In general, particles greater than 10 m (mi- Food contamination with toxic chemicals is also possible. crometers, also called microns) in diameter are trapped by Although only isolated cases of intentional food poisoning nasal hairs and released with exhaled air or sneezing. Parti- have occurred, several single accidental food poisoning cles less than 10 m in diameter are referred to as "inhalable" events within the last decade have sickened thousands of peo- because they may pass into the upper portions of the lungs, ple, suggesting the potential effects that could be achieved which contain many branched passageways. These passages with intentional food poisoning. (bronchi and terminal bronchioles) are lined with mucus and cilia. The mucus traps particles, and the cilia gradually push the mucus and its contents up and out of the lungs within Dispersion, and Population Density about a day. Chemical agents trapped in the mucus are then swallowed, entering the digestive tract. The smallest parti- The density of the population in the area at risk affects the cles or aerosols (e.g., less than 2.5 m diameter) are referred means for communicating instructions and the choices of to as "fine" or "respirable" particles. Fine particles may pass transportation-related responses. The number of individuals into the deepest portions of the lungs (i.e., respiratory bron- at risk during a chemical event depends on the population chioles, alveolar ducts, and alveolar sacs) where they may density and the area over which health-threatening levels of dissolve or be removed by macrophages over many days. contamination are dispersed. Health-threatening levels are The unaided human eye can discriminate individual par- determined by the type and toxicity of the chemical and the ticles down to the size of 30 microns. These particles will exposure route. Dispersion is determined from the physical be trapped by nose hairs and mucous and blown out or form of the chemical (i.e., gas, liquid, solid, or particles), swallowed before reaching the lungs. To put particle sizes topology and meteorology (i.e., rain and wind currents), and in perspective, particle size of commonly used substances the quantity released. are presented in Table 2-5. One of the more common worst-case scenarios of a chem- Absorption through skin is the primary exposure route for ical incident involves the release of a chemical that is a gas some chemical weapons agents (i.e., essentially all blister under ambient conditions, but is transported as a liquid under agents and some nerve agents). Many of the agents for which pressure in 90-ton railroad tank cars. A release from one of the skin is a primary exposure route are oily liquids. Aerosol these cars carrying chlorine or ammonia has been projected droplets too large to be readily respired are a common means to create a danger zone in the range of 14 miles--in a highly for dispersal of these agents. Droplets of some of these agents urbanized area, such a release could affect millions of peo- (e.g., VX) can take weeks to evaporate or break down to less ple. When pressurized liquids are released, part of the liquid toxic forms. Many common fabrics provide protection from immediately flashes to a gas, forming a vapor cloud. The re- skin absorption of some agents (e.g., the blister agent phos- mainder may be fragmented into fine liquid droplets (i.e., an gene oxime), but provide little protection from other agents aerosol), which will soon evaporate. Depending on the re- (e.g., sulfur mustard). lease conditions, some of the liquid may form an evaporat- Ingestion of chemical toxins may occur with tainted drink- ing liquid pool on the ground. The highly turbulent nature of ing water or food. An effective chemical toxin release in these releases facilitates mixing with air. Within a minute, the drinking water supply of a city-sized population gener- the cloud typically consists of air with a few percent of the ally is not viewed as a credible threat by terrorism experts be- released chemical. The vapor cloud is heavier than air, caus- cause of the quantity of an agent needed and the degradation ing it to slump to the ground, becoming a broad cloud that of chemicals that results from standard water disinfection backs up against the wind. Within a few minutes, a release processes. However, a chemical attack on post-purification of common bulk transport quantities of a liquefied gas drinking water storage in a small municipality or a specific (i.e., 20 to 90 tons) can cause a vapor cloud with a backup of building is viewed as more credible, but difficult to get several hundred meters and a width of a kilometer or more. without site-specific knowledge and access. By extension, Depending on atmospheric conditions, the size of the release, intentional chemical contamination of passenger drinking and the toxicity of the released gas, the area of concern may TABLE 2-5 Individual Particle Size of Commonly Used Substances Substance Individual Particle Size (Microns) Inhalable / Respirable Beach sand 74 to 187 No Table salt crystal 100 No Powdered confectioner's sugar 10 Inhalable Talc powder 1.5 to 37 Inhalable and Respirable Tobacco Smoke 0.5 Inhalable and Respirable