Decontamination varies with the particular chemical agent used. Some nonpersistent agents, such as most pulmonary agents such as chlorine and phosgene, blood gases, and nonpersistent nerve gases (e.g., GB) will dissipate from open areas, although powerful exhaust fans may be needed to clear out buildings where they have accumulated.
In some cases, it might be necessary to neutralize them chemically, as with ammonia as a neutralizer for hydrogen cyanide or chlorine. Riot control agents such as CS will dissipate in an open area, but things contaminated with CS powder need to be aired out, washed by people wearing protective gear, or safely discarded.
Mass decontamination is a less common requirement for people than equipment, since people may be immediately affected and treatment is the action required. It is a requirement when people have been contaminated with persistent agents. Treatment and decontamination may need to be simultaneous, with the medical personnel protecting themselves so they can function.
There may need to be immediate intervention to prevent death, such as injection of atropine for nerve agents. Decontamination is especially important for people contaminated with persistent agents; many of the fatalities after the explosion of a WWII US ammunition ship carrying mustard gas, in the harbor of Bari, Italy, after a German bombing on 2 December 1943, came when rescue workers, not knowing of the contamination, bundled cold, wet seamen in tight-fitting blankets.
For decontaminating equipment and buildings exposed to persistent agents, such as blister agents, VX or other agents made persistent by mixing with a thickener, special equipment and materials might be needed. Some type of neutralizing agent will be needed; e.g. in the form of a spraying device with neutralizing agents such as Chlorine, Fichlor, strong alkaline solutions or enzymes. In other cases, a specific chemical decontaminant will be required.