Environmental Protection Agency

EPA Acute Exposure Guideline Levels for CS Gas

Tear Gas (o-Chlorobenzylidenemalonitrile; CAS No. 2698-41-1) is a white crystalline powder with a pepper-like odor. It was first synthesized by Corson and Stoughton in 1928 (thus the abbreviation “CS”). It was developed in the 1950s as a replacement for the chemical incapacitant CN (1-chloroacetophenone) used by police because CS was a much more potent irritant than CN, but was significantly less toxic.