Abstract: Chlorine-containing gases which may be formed in containers of solid chloroisocyanurates such as trichloroisocyanuric are adsorbed and decomposed by a gas scavenging agent consisting essentially of an alkaline earth metal sulfate, an alkali metal bicarbonate, and carbon. The gas scavenging agent is preferably contained in a gas permeable package which is enclosed in the container. The scavenging agent adsorbs mositure, adsorbs and decomposes nitrogen trichloride, removes chlorine, and neutralizes hydrogen chloride gases formed. Harmful build-up of noxious gases and the reduction of gas pressures within containers for solid chloroisocyanurates is achieved.