In 1959, the US Army adopted CS (orthochlorobenzalmalononitrile) for combat training and riot control purposes. The Army found it to be both safe and effective, especially for training and creating combat realism in low concentrations. Only CS in a capsule form could be used in the CS training chamber. In Vietnam, CS was an effective incapacitant while its variable persistency made it an economical contaminant. Different forms of CS had different persistence characteristics, due to their formulation, dissemination, and rate of hydrolysis. CS is normally used either as a pure powder in bulk form or as pellets in a pyrotechnic mixture for employment in burning grenades and bomblets ("Tear Gas"). A yellowish powdered solid in pure form, CS has a characteristic pungent pepper-like odor. Employed in aerosol form, CS irritates the eyes, nose, throat, and (if used in sufficiently high concentration) will cause militarily significant incapacitation. By weight, the effectiveness of CS is about 10 times that of its predecessor CN. The symptoms of exposure to training concentrations of CS are:
- Extreme burning of the eyes, with much tearing, coughing, and difficulty in breathing with tightness in the chest and pain in breathing.
- Involuntary closing of the eyes.
- Heavy mucous formation in the nose with sinus and nasal drip.
- Stinging or burning on moist skin areas.
Exposure to field concentrations may cause nausea and vomiting and prolonged exposure to CS on skin may cause severe irritation and blistering. Incapacitation is caused by the individual's inability to see or preoccupation with the agent's effects. Effects of the agent appear almost immediately and will continue as long as the individual is exposed. Affected individuals usually recover within 10 minutes in fresh air. CS has been specially formulated for varied dissemination characteristics and/or effects as CSX, CS1, and CS2. CSX is a form of CS developed for dissemination as a liquid rather than a powder. One gram of powdered CS is dissolved in 99 grams of solvent trioctyl phosphate (TOF) and is dispersed as a liquid aerosol from the M32 hand-held disperser. As with CS, CSX causes stinging and irritation of the eyes, skin, nose, throat, and lungs of exposed personnel. It is only available in M32 hand-held dispersers.
Variations in the formulation of CS result in different persistencies for CS, CS1, and CS2. CS originating from burning munitions is disseminated only as an airborne cloud and its persistence depends mainly on air movement. The aerosol particles, once contacting the ground or other surfaces, adhere and do not re-aerosolize. Due to the relatively low volatility and rapid rate of hydrolysis, the CS aerosol usually presents a negligible residual hazard. However, a certain amount of caution must be exercised, since pockets of the airborne agent may linger in closed structures or other places where movement of air is slight.
CS1 has been specially formulated to prolong persistency and increase effectiveness. Unlike CS, CS1 is free-flowing agent powder (95 percent CS to 5 percent silica aerogel), that is readily usable in disseminating devices (for example, spray tanks) that require a free-flowing material. CS1 is CS blended with silicone-treated silica aerogel which not only prevents coagulation and increases fluidity, but also markedly increases its resistance to water. This form of CS prolongs the effectiveness for both immediate and surface contamination effects for direct and residual use. As CS1 settles out of the air, it readily contaminates terrain, vegetation, personnel, and equipment. When disturbed, CS1 re-aerosolizes to cause respiratory and eye effects.
CS1 exhibits typical CS activity for several days on dry ground at initial incapacitating concentrations (5-10 mg/m3). Persistency tests have shown that CS1 can remain effective for about 14 days when used inside a dry tunnel or bunker and about 7 days on open terrain under ideal environmental conditions.
CS2 is far more resistant to water degradation, maintaining an effectiveness for a period approximately double that of an equivalent initial concentration of CS1. It is so resistant to wetting that when spread upon the surface of a body of water, agitation of the surface by wind or wading may regenerate an effective aerosol. CS2 will remain effective on open terrain under suitable conditions for about 30 days. Although rain does not effectively dissolve the agent, it may physically wash away from the site of deposit. High winds will dissipate it.