Materials producing smoke screens are rated in units for their top obscuring power (TOP). TOP is a relative value that indicates the amount of obscurity (due to reflection and refraction of light rays) that 1 pound of smoke-producing material will develop under standard and controlled conditions against a 25-candlepower light source.
The principal smoke-producing agents, ordered according to their obscuring powers, are treated below:
a. White phosphorus (WP), with a 3,500 unit TOP, is a white to light yellow, waxlike, luminous substance (phosphorescent in the dark). On ignition, it produces a yellow-white flame and dense white smoke. WP is poisonous when taken internally; its smoke or fumes are not. When dispersed by ammunition, as small particles, WP ignites spontaneously on exposure to air. It continues to burn on contact with solid materials, even when embedded in human flesh. WP smoke is unpleasant to breathe but harmless. The particles, however, will poison food and water. WP is used in bursting-type projectiles, artillery and mortar rounds, grenades, rockets and bombs. It is used as an igniter in incendiary ammunition that contains flammable fuels (IM, NP, PT1). When used in projectiles that burst on terrain covered with soft deep snow, it is smothered and produces approximately 75 percent less smoke.
b. Plasticized white phosphorus (PWP) is a finely divided form of WP suspended in a thick-ended and gelled xylene rubber mixture. Like WP, it is an effective, double-purpose, screening and incendiary agent that can be dispersed under arctic and tropic conditions, and in temperate zones.
c. Sulfur trioxide-chlorosulfonic acid (FS), with a 2,240 unit TOP, is a liquid with an acrid and acid odor. It produces dense white smoke when dispersed in a humid atmosphere. FS smoke is nonpoisonous; however, its liquid irritates and inflames skin tissue on contact. A protective mask is required for protection against exposure to heavy concentrations. The mask and protective clothing should be used for protection against combination FS gas and liquid sprays. Liquid FS renders food and water unfit for use; the smoke merely imparts an unpleasant taste. Liquid FS possesses the corrosive properties of strong mineral acids, such as sulfuric or hydrochloric. Accordingly, during use and handling, stringent precautions should be observed for protecting nonaggressor personnel and noncombat forces and materiel. FS is dispersed from mortar rounds, grenades and by aircraft spray from cylinders. Under tropical and high humidity conditions, FS performs very effectively. FS is ineffective as smoke under conditions of low temperature and low humidity.
d. Hexachloroethane-zinc mixture (HC), with a 2,000 unit TOP, is a combination of zinc powder, hexachloroethane, ammonium perchlorate and ammonium chloride. When ignited, it produces zinc chloride that passes into the air as a dense grayish-white smoke. HC is toxic to unprotected personnel exposed to heavy concentrations for short periods or to light concentrations for extended periods of time. A protective mask offers adequate protection against light concentrations. For heavy concentrations and prolonged exposure, a self-contained oxygen mask is required. Food and water are not spoiled by HC, but acquire a disagreeable odor. HC in canisters, dispersed by base-ejection artillery projectiles, is not effective for use on terrain covered with deep loose snow. Under these conditions, canisters bury themselves and become smothered. However, they can be employed effectively on hard packed snow or ice. HC is dispersed effectively from fixed and floating smoke pots, base-ejection artillery projectiles, mortar projectiles and grenades under favorable (humid atmosphere and hard terrain) arctic or tropic conditions, or in temperate zones.
Incendiaries are agents that can be used under field conditions to set fire to buildings, industrial installations, ammunition and fuel dumps, and so forth. Modern military incendiaries may be divided into three categories-oil, metal, and a combination of oil and metal. Incendiaries may also be classified as those which owe their effect to a self-supporting, heat-generating reaction and those which, for their combustion, depend upon oxygen in the surrounding atmosphere.
a. Thermite (TH) is an intimate, uniform mixture of approximately 27 percent powdered aluminum and 73 percent iron oxide. On ignition, it produces intense heat (approximately 4,300°F.) in a few seconds, with the formation of a white hot mass of molten iron and slag. TH is used in cartridges, bombs, grenades and mortar and artillery projectiles. TH-1 as a filler is included in thin-walled nonmagnesium metal containers.
b. Thermate (TH-3 and TH-4) is essentially a thermite, barium nitrate, sulfur and binder contained in a heavy-wall body, usually magnesium or a magnesium alloy. When initiated by electrical or mechanical means, the contents and body burn with an intense heat of about +3,700°F. Thermate fires are difficult to extinguish.
c. Magnesium, in fine powder, thin ribbon or solid form, is a material that ignites and burns with intense heat (3,630°F.) and white light. It is used extensively in pyrotechnic mixtures and incendiary munitions.
d. Incendiary oil (IM), such as an 88 percent gasoline mixture thickened with fatty soaps, fatty acids and such special chemical additives as isobutyl methacrylate polymer and naphthenic acid, is a typical example of a thickened fuel. It may or may not contain metallic sodium or WP particles for ignition. In addition, small amounts of a peptizer, such as cresylic acid, are added to aid in cold weather dispersion. When dispersed and ignited, IM adheres to both combustible and noncombustible surfaces. It burns like ordinary gasoline with a hot orange flame and gives off a black smoke. IM is used as a filler in bombs, grenades and portable and mechanized flame-throwers. Winterized IM incendiary fuels can be dispersed from bombs or grenades and is effectively employed under arctic conditions.
e. Incendiary oil, napalm (NP), is a flammable fuel, principally aviation gasoline (approximately 88 percent), thickened with a special gelling mixture of fatty acids, fatty soaps and antiagglomerate additives. As a filler, with or without metallic sodium or WP particles, NP can be used in munitions in the same manner as IM.
f. Incendiary mixtures (PT1 and PTV) are complex mixtures of gasoline, magnesium, thickening agents and conditioning agents. The same type of incendiary effect is obtained with PT1 and PTV as with oil incendiaries.
Flame-thrower fuels are either unthickened or thickened gasoline and oil mixes. When dispersed and simultaneously ignited by mechanical, electrical or chemical means, they cause destruction of materiel and casualties by burning or scorching with hot flame. The main flame-thrower fuels are as follows:
a. Unthickened fuels consisting of gasoline blended with light fuel oils or lubricating oils. Ingredient proportions are determined by the tactical situation and type of climate in which the flame-thrower is to be used. Unthickened fuel is used only in portable flamethrowers. It may be used when thickened fuel is not available or may be used in jungle operations.
b. Thickened fuels consisting of a fuel, mainly gasoline, gelled with aluminum soap thickeners or rubber-type thickeners. Thickened fuel increases the range of flame-throwers, imparts slower burning properties, gives clinging qualities, and causes flames to rebound off walls and go around corners.
(1) Molasses residuum (MR) is a nontoxic (25 percent solution) of a thick, syrupy, viscous liquid with a molasses odor. It is used as a simulant for mustard (H or HD) agent.
(2) Asbestine suspension (AS) is a nontoxic suspension of finely ground asbestos in water. It may or may not include butyric acid, a material that imparts a disagreeable lingering scent like rancid butter. With butyric acid, AS is known as an asbestine-butyric acid suspension; without butyric, it is known as an asbestine suspension. AS is dispersed as a spray from aircraft. When dispersed, it will adhere like MR to surfaces and personnel and show up in contrast to the surrounding medium.
b. Chlorine. Chlorine, a choking agent, was the first chemical agent to be dispersed on a major scale in wartime. It was released by the Germans against the British during World War I. Chlorine is no longer used as a war gas, having been succeeded by phosgene and diphosgene. However, it is still used for training purposes.
2-29. Marking and Identification a. All ammunition containing chemical agents is identified and marked with distinctive symbols or letters and colors, as indicated in chapter 1.
b. For the purpose of storage, chemical agents and munitions are segregated into four groups, according to the nature of the filling and their inherent hazards as follows:
(1) Group A- (blister and nerve gases)-includes chemical agents requiring complete protective clothing plus protective masks.
(2) Group B - (toxic and smoke)-includes chemical agents requiring protective masks.
(3) Group C - includes spontaneously flammable chemical agents, such as WP.
(4) Group D - includes incendiary and readily flammable chemical agents.
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