Agent CS (Orthochlorobenzylidenemalononitrile) was first prepared in 1928 by two American chemists, Ben Corson and Roger Stoughton. (The CS initials were taken from the first letters of the names of the discoverers). However, it remained until 1956 for the British CBW laboratory at Porton Down, the Chemical Defense Experimental Establishment, to develop CS as a riot control agent. CS was first used on a large scale by the British in the Cyprus riots. In 1960, CS was officially adopted by the United States Army for use in riots.
CS in its pure form is a white crystalline powder resembling talcum powder. It is classified as an irritant agent and lachrymator. Since it is made of solid particles, it must be carried through the air by an agent or expelled in a fine dust. The odor is rather pungent.
CS causes burning and lacrimation of the eyes as well as irritation of the skin and respiratory system. The burning effects of the eyes and skin will be similar to CN and the irritation of the respiratory system will result in sneezing. It could take many seconds before the effect of CS is realized. CS is most irritating in a humid climate and on a moist skin surface. Anyone who has lost his sense of feeling because of the influence of narcotics or alcohol will not be affected by CS.
CS is a lachrymator and sneeze producer at levels as low as 0.05 mg/m3. The powder CS is designated CS1 and is much more durable than the aerosol form of the agent. As a further refinement, CS1 is coated with silicone to extend its field persistence up to several weeks; the weatherproofed variety is called CS2.
Being extremely persistent, CS causes a severe area decontamination problem. Particles disseminated by any of the standard means of dispersion will adhere to the person, clothing, furnishings, or fixtures for long periods. Humid conditions will cause the odor and irritant effect to linger indefinitely.
Decontamination is achieved by using an alkaline solution. A solution of water and 5% sodium bisulfite is usually employed for decontamination.
CS is less toxic than CN and has only transient effects on the eyes. However, both CS and CN cause dermatitis and are sensitizers that may cause very serious allergic reactions upon repeated exposure. Toxicological tests demonstrated that animals dying after exposure to CS show increased counts of goblet cells in the respiratory tract and conjunctiva (the mucous membrane in the eyes, lining the eyelid and covering part of the eyeball), necrosis (the death of cells) in the respiratory and gastrointestinal tract, pulmonary edema (lungs filled with fluid), and hemorrhage in the adrenal. Death results from impaired oxygen transfer to the blood stream as a result of edema, hemorrhage, and obstruction of the air passages in the lungs. In the case of a substance such as CS, attention must be directed to the breakdown products that will occur in the human body. Cleavage or hydrolysis into malononitrile and ortho-chlorobenzaldehyde is a reaction that is 50% complete in about ten minutes. The malononitrile is believed to suffer degradation to cyanide and thiocyanate whereas the remainder of the molecule is combined with glycine and excreted as ortho-chlorohippuric acid. Therefore malononitrile is a highly toxic substance found in CS. The mortal dose for a 150 pound person is estimated to be about a gram or less.