... 1 .First class: chemical agent: Hydrocyanic acid, cyanogens chloride, arsine, phosgene, chloropicrin, bromomethane, lewisite gas, mustard gas, sarin, vx gas, toxic smoke, ... 21kg 4.Usage maintenance and maintain4.1.The selection of gas mask 4.1.1. checking the position between glasses and ... without any air leakage that means a right selection. 4.2.The procedure of wearing gas mask 4.2.1. adjusting the ...