Medical Aspects of Chemical Warfare (2008) - The Black Vault

Medical Aspects of Chemical WarfareCS (o-chlorobenzylidene malononitrile)CS (also known as 2-chlorophenyl-methylenepropanedinitrile,β,β-dicyano-o-chlorostyrene, and2-chlorobenzalmalononitrile) is the US military’smost widely used RCA compound in operations andtraining. CS was first synthesized by British scientistsCorson and Stoughton (hence its name) in 1928 bycondensing aromatic aldehydes with malononitrile. 24Corson and Stoughton showed CS to have an intensenasal (sneezing) and skin irritant effect and noted thatexposure to it caused the “face to smart.” This outcomecan be minimized by wearing a protective mask, butmay be temporarily intensified if the exposed area isrinsed with water. 24 These characteristics made CSa notable candidate for widespread adoption as amilitary incapacitant. However, CS wasn’t readily acceptedfor this use until well after World War II, whenit was learned that the effect of CS was less toxic butmore potent than that of CN. As a result, the US ArmyChemical Corps declared CS its standard military RCAon June 30, 1959. 25 See Table 13-1 for a summary of CScharacteristics.Other symptoms of CS exposure, which may be associatedwith bradykinin release, consist of irritationand a burning sensation of the eyes, nose, skin, andthroat, resulting in the need for exposed individualsto close their eyes and hold their breath, quicklyrendering them incapacitated. 26,27 Recent scientificinvestigations into the identification of CS-derivedcompounds and other thermal degradation productsformed during the heat dispersion of CS have raisedquestions about the potential health risks associatedwith the use of high-temperature heat dispersiondevices, particularly if used in enclosed spaces. 28–31It is critical that CS be deployed in accordance withexisting training guidance to minimize its potentialhealth hazards.Physical Characteristics and DeploymentPhysical CharacteristicsCS is a gray, crystalline solid with a pepper-likeodor. Additional characteristics are a molecular massof 188.6 d; molecular formula of C 10H 5ClN 2(Figure13-1); melting point of 95°C to 96°C; boiling point of310°C to 315°C; low vapor pressure of 3.4 × 10 -5 mmHg at 20°C; slight solubility in water; solubility at 25°Cin the organic solvents methylene chloride, acetone,ethyl acetate, benzene, and dioxane; and half-life of14 minutes at pH 7.4 and 25°C. Dissolved CS is rapidlyhydrolyzed to form o-chlorobenzaldehyde andmalononitrile. 32DeploymentCS rapidly loses its effectiveness under normal environmentalconditions, making it an ideal temporaryincapacitant. The US Department of Defense created atleast three variations of CS—CS1, CS2, and CSX—allof which are used today. CS1 is a micronized powderconsisting of 95% CS and 5% silica aerogel designedto reduce agglomeration. CS2 is a siliconized microencapsulatedform of CS1 comprised of 94% CS, 5%colloidal silica, and 1% hexamethyldisilizane, whosecharacteristics increase shelf life, resistance to degradation,and the ability to float on water, thus providing ameans of restricting key terrain during military operations.33 CSX is comprised of 1 g CS1 dissolved in 99 gtrioctylphosphite, enabling dissemination as a liquid.CS powder is usually delivered as a component of anaerosol, solution, explosive device, or smoke. 34The mechanism of deployment typically involvesthe use of storage cylinders, mortars, artillery projectiles,grenades (Figures 13-2 and 13-3), cartridges,aircraft or vehicle-mounted dispensers, portable dispensers,or personal protection dispensers. 34 Regardlessof the delivery mechanism, CS exposure causesalmost immediate inflammation of the conjunctivae,tearing (lacrimation), pain, and involuntary closureof the eyes and lids (blepharospasm). Respiratoryeffects include sneezing, nasal discharge, and throatirritation, often accompanied by violent coughing.Continued CS exposure results in tightness of chestand general breathing difficulty. These effects resolvewithin minutes of removal from the exposure, andonly moderate tearing and redness of the eyes remain10 minutes after exposure. 35,36In addition to its use by the United States in Vietnam,during demonstrations and prison riots, andfor military and law enforcement training, 36 CS wasused by British police to quell riots in Londonderryin August 1969. 37,38 CS has an extensive mammaliantoxicology database. 2Thermal Degradation ProductsCS is commonly used as an RCA and chemical warfareagent simulant for training, in which law enforcementand military employees are routinely exposedto heated CS. Heat assists in the dispersion processby vaporizing the CS, which then condenses to forman aerosol. Heat dispersion of CS has the potentialto form CS-derived compounds that have been thefocus of many recent studies. Thermal dispersion ofCS from a canister in an enclosed space was shown to444