Identification of Compounds Formed During Low Temperature Thermal Dispersion of Encapsulated o-Chlorobenzylidene Malononitrile (CS Riot Control Agent)

Abstract

U.S. Army chemical mask confidence training is conducted in an enclosed chamber where airborne o-chlorobenzylidene malononitrile (also known as CS or “tear gas”) is generated using a low temperature (150–300°C) dispersal method. CS capsules are placed onto a flame-heated aerosol generator that melts the capsules and disperses CS into the chamber. To instill confidence in chemical protective equipment, trainees are required to break the seal of their chemical protective mask, resulting in the immediate irritation of their eyes, nose, throat, and lungs. Solid phase micro extraction (SPME) sample collection techniques were used inside the chamber, followed by gas chromatography and mass spectrometry (GC/MS) to identify unintended thermal degradation products created during the CS dispersal process. The temperature of the aerosol generator averaged 257°C, and 17 thermal degradation products were identified. To characterize the relationship between temperature and the types of CS thermal degradation products formed, CS was dispersed in a tube furnace at controlled temperatures from 150–300°C and analyzed using the same method. There was a graded response between temperature and the number of thermal degradation products formed, with one product formed at 150°C and 15 products formed at 300°C. Two additional products were identified in the chamber experiment when compared with the tube furnace experiment. These products are likely the result of molten CS dripping directly into the aerosol generator's flame, which averaged 652°C. To prevent undesirable degradation products during thermal dispersion of CS, a delivery system designed to contain the molten CS and maintain a consistent temperature near 150°C is recommended.