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27 contamination is typically achieved with vacuum cleaners or TABLE 2-12 Determination of high-pressure water washing with suitable cleaners or deter- Radiological Event Emergency gents. Personnel working in decontamination areas would Response require proper protective gear, and waste from these areas Radiological Event would be disposed of as radioactive waste. Typically, the Information Needed to Determine ease of decontamination is inversely related to surface ad- Appropriate Emergency Response sorptivity. Thus, smooth surfaces, such as new cars and the Estimated population exposed to levels of outside of aircraft, are more easily decontaminated than concern as determined from: Affected area information (see below) rough surfaces, such as asphalt, concrete, terminals, stations, Population data vehicle interiors, and so forth. Estimated affected area as determined from: In the more limited range of a pressure wave from a con- Exposure pathway information (see below) ventional explosion, radioactive particles may actually pen- Amount of material Location of release etrate surfaces, rather than just lie on or adhere to the surface. Wind direction and strength In these cases, the top surface layers of road, tunnel, or walls Topography nearby the blast area may need to be removed and disposed Possible exposure pathways as determined of as radioactive waste. There is no generally accepted guide from: on the most appropriate methods for dealing with long-term Radiation type Physical form (gas, liquid, solid) radioactive contamination of large surfaces that are difficult Specific radioisotope to decontaminate (i.e., asphalt and concrete). Handling of these cases is likely to be controversial and may vary de- pending on the location, expected surrounding population, and size of the contaminated area. Quantity and Persistence In marine scenarios, pumped seawater could be effective in removing contamination from ships, docks, and other The quantity of radioactive material released, in conjunc- modes of transportation present in the harbor. If a radiologi- tion with radiation type and specific radioisotopes, deter- cal release is small enough and does not adhere to surfaces, mines the persistence as a health threat. Gaseous and liquid it may be acceptably cleaned within a week; however, de- forms may be diluted to background levels. Releases of types contamination of surface radioactivity generally can be ex- of radioactivity with a short half-life may be isolated and pected to take anywhere from weeks to years, depending on contained until it has decayed to safe levels. Radioactivity its magnitude and tenacity. with a very short half-life is not among the common threat scenarios. Of the more commonly discussed RDD compo- nents, Co-60 may have the shortest half-life (5.27 years). 2.3.2 Emergency Response Information Needs Thus, isolation of areas with Co-60 contamination for a decade would reduce radiation levels to about a quarter of the Regardless of the cause of a radioactive release, from an initial levels. In any case, the feasibility and cost of deconta- emergency response perspective, the primary considerations mination would be a significant consideration along with the for response management are: radiation type and energy, value of the contaminated area. quantity and persistence, exposure route, and dispersion and population density in the area at risk. Table 2-12 delineates the information needed to decide transportation goals for isolation, shelter-in-place, evacuation, and checkpoint es- Exposure Route tablishment in a radiological event. These factors and their The expected exposure route needs to be assessed for ap- interrelationship are further discussed below. propriate risk management. As stated above, radiation type and energy determine the likely exposure routes, in con- Type and Energy junction with the physical form of the radioactive material as a gas, liquid, or solid. Inhalation is the primary exposure The type and energy of a radioactive material, and its quan- route of concern for a gas that contains radioactive materi- tity, determine the extent of shielding or distance needed to als (i.e., unstable atoms that release radiation). Depending protect people from radiation. The type and energy of the ra- on the type and energy of a radioactive gas, exposure diation also determine what exposure routes are most likely through the skin may also be possible. A radioactive liquid to cause human health effects. For example, low-energy alpha would pose the greatest threat when introduced into a radiation cannot penetrate the skin, but can be damaging if it potable water system or other drinks, thereby allowing in- is ingested or inhaled. In contrast, beta and gamma radiation gestion. As with gaseous radiation, depending on the type can pass through the skin (i.e., external direct exposure), and and energy of radioactivity in a liquid, radiation may pass be inhaled or ingested. from the liquid through the skin.