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visible and infrared radiation or microwaves. Fog, mist, and dust are examples of obscurants. Smoke is an obscurant normally produced by burning or vaporizing some product.

The selection of obscurants used during a military operation depends on the tactical needs. For example, visual obscurants, which block visible light and the near-infrared portion of the electromagnetic spectrum, are used to block viewers, such as binoculars, weapon sights, night-observation sights, and laser-range finders. Bispectrual obscurants, which also block light in the far-infrared portion of the spectrum, hinder battlefield viewers and weapons-guidance systems, such as homing systems on antitank- and air-defense missiles. Other multispectrual obscurants can defeat radar systems and high-energy microwave-directed weapons.

SMOKES REVIEWED IN THIS REPORT

The effectiveness of obscuring and screening smokes depends on their ability to obscure visibility by reflecting, refracting, and scattering light rays. For this reason, all such military smokes consist of aerosols with particle dimensions approximating the wavelength of visible to near-infrared light. The relationship between smoke concentration and the associated reduction in visibility is summarized in Table 1-1 for selected smokes. As the smoke concentration increases, the obscurant effectiveness increases as indicated by the decreasing visibility.

Among the most widely used smoke munitions in actual combat are those that produce smoke by burning a mixture of chlorinated hydrocarbons and zinc oxide (ZnO). The hydrocarbon generally used in these smoke mixtures is hexachloroethane (HCE), and the generic name the military attaches to the HCE-ZnO smokes is hexachloroethane smoke or HC smoke. Most of the HCE-ZnO mixture produced for the military is used in smoke pots or cylindrical metal canisters containing the HCE-ZnO mixture along with a pyrotechnic charge that, when ignited, provides the heat necessary to generate the HC smoke. Smoke pots ordinarily are used to provide small-area screens, supplement other smoke



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