A Study for Health Hazard Evaluation of Methylene Chloride Evaporated from the Tear Gas Mixture

This study explored the health hazard of those exposed to methylene chloride by assessing its atmospheric concentration when a tear gas mixture was aerially dispersed. The concentration of methylene chloride ranged from 311.1–980.3 ppm (geometric mean 555.8 ppm), 30 seconds after the dispersion started. However, the concentration fell rapidly to below 10 ppm after dispersion was completed. The concentration during the dispersion did not surpass the National Institute for Occupational Safety and Health (NIOSH) 'immediately dangerous to life or health' value of 2,300 ppm, but did exceed the American Conference of Governmental Industrial Hygienists (ACGIH) excursion limit of 250 ppm. Since methylene chloride is highly volatile (vapor pressure, 349 mmHg at 20 °C), the post-dispersion atmospheric concentration can rise instantaneously. Moreover, the o-chlorobenzylidenemalononitril e formulation of tear gas (CS gas) is an acute upper respiratory tract irritant. Therefore, tear gas mixtures should be handled with delicate care.