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THE U.S. CHEMICAL WEAPONS STOCKPILE 37 2 The U.S. Chemical Weapons Stockpile This chapter presents a brief description of the U.S. chemical weapons stockpile, covering the physical properties of chemical agents, their toxicities, associated weapons, and the nature and distribution of stockpile storage sites. DESCRIPTION OF THE AGENTS The U.S. chemical weapons stockpile contains nerve agents, or nerve gas, and blister, or mustard, agents. (Mustard was used extensively in World War I, whereas nerve agents were first used in war by Iraq in its war with Iran.) These two fundamental types of chemical warfare agents are contained in the U.S. stockpile in a variety of munitions and bulk containers. Nerve agents in the U.S. stockpile include persistent VX, nonpersistent Sarin (GB), and a small quantity of Tabun (GA). All the nerve agents are organophosphonate compounds, which contain phosphorus double-bonded to an oxygen atom and single-bonded to a carbon atom. VX also contains sulfur in its chemical structure, GB contains fluorine, and GA contains the cyanide group (see Figure 2-1 for the chemical structures of major U.S. chemical agents and Table 2-1 for some of their physical properties).1 Nerve agents are highly toxic or lethal in both liquid and vapor forms.2 Although they are often referred to as gases, they are liquids at normal 1 VX is O-ethyl-S-[2-diisopropyl aminoethyl]methylphosphonothiolate; GB is isopropyl methyl phosphonofluoridate, and GA is ethyl-N, N-dimethyl phosphoramidocyanidate. 2 Terms used in the literature include: lethal, danger of quick death on exposure; toxic, serious impairment of health, or even death, on substantial exposure; poisonous, dangerous if not handled carefully (e.g., gasoline or household bleach); and hazardous, known or suspected to pose a risk to human health or the environment. In this report, the term toxic is sometimes used in a general sense, encompassing all levels of toxicity.
THE U.S. CHEMICAL WEAPONS STOCKPILE 38 FIGURE 2-1 Principal chemical wadare agents in the U.S. stockpile. temperatures and pressures. GB has a boiling point about 5°C lower than that for kerosene or diesel fuel. It evaporates at about the same rate as water and is relatively nonpersistent in the environment. VX evaporates much more slowly, and spills of liquid VX can persist for a long time under average weather conditions. Thus, GB presents mainly a vapor hazard, although contact with its liquid form can also be fatal. In contrast, VX presents mainly a contact hazard, although its vapor buildup in enclosed spaces can also reach lethal levels. In their pure form, all these nerve agents are nearly odorless and colorless. The blister agents include H, HD, and HT. The active ingredient in H and lid and a major component (60 percent) of HT is the same chemical substance, bis(2-chloroethyl)sulfide, or mustard.3 The agent H, sometimes called Levinstein mustard, contains 70 percent mustard and 30 percent 3 Mustard gas, sulfur mustard, yperite, and other names have also been applied to this agent. Although 'mustard gas' is often used, the chemical is a liquid at ordinary ambient temperatures; its initial boiling point is comparable with that of the more volatile parts of kerosene.
TABLE 2-1 Physical Properties of Chemical Warfare Agents Agent Characteristic Nerve Agents Blister (Mustard) Agents GB (Sarin) VX H/HD HT Chemical formula (CH3)2CHO(CH3 )FPO C11 H26NO2PS (ClCH2CH2)2 S 60% (ClCH2CH2)2S, 40%sulfur and chlorine compounds Molecular weight 140.10 267.38 159.08 Not available Boiling point, °C 158 298 217 228 Freezing point, °C -56 < -51 14.45 0 to 1.3 Vapor pressure, mm Hg 2.9 @ 25°C 0.0007 @ 25°C 0.072@ 20°C Not available Volatility, mg/m3 4,100@ 0°C 10.5 @ 25°C 75 @ 0°C (solid) 831 @ 25°C 22,000@ 25°C 610 @ 20°C (liquid) Diffusion coefficient for vapor in air, cm2/sec 0.061@ 20°C 4 @ 20°C 0.060@ 20°C 0.05@ 25°C Surface tension, dynes/cm 26.5@ 20°C 32.0@ 20°C 43.2@ 20°C 44 @ 25°C Viscosity, cS 1.28@ 25°C 12.256@ 20°C 3.95 @ 20°C 6.05@ 20°C THE U.S. CHEMICAL WEAPONS STOCKPILE 39
Agent Characteristic Nerve Agents Blister (Mustard) Agents GB (Sarin) VX H/HD HT Liquid density, g/cm3 at 20°C 1.0887 1.0083 1.2685 Not available Latent heat of vaporization, cal/g 80 78.2 94 Not available Solubility, g/100 g of distilled water 100; soluble in organic solvents 5 @ 25°C; best solvents are dilute 0.92 @ 22°C; soluble in acetone, CCl4, mineral acids CH3Cl, tetrachloroethane, ethyl benzoate, ether Heat of combustion, Btu/lb (cal/g) 10,000 15,000 8,100 Not available (5.55) (8.33) (4.5) Source: Chemical Systems Laboratory (1983); Programmatic Environmental Impact Statement (PEIS) (1988). U.S. Departments of the Army and Air Force (1975). THE U.S. CHEMICAL WEAPONS STOCKPILE 40
