Decontamination is the work of removing a dangerous substance and making a place, a person, or a piece of equipment safe again. After a chemical spill or a radiation leak, you hear about a decontamination area, where people are washed down before they leave. It names the whole process — the washing, the special gear, the checks — not one wipe with a cloth. The verb is decontaminate; this noun is the job itself. Though actually, the word can sound calmer than the situation: decontamination after radiation may take a long time, and 'done' does not always mean 'forgotten.' In ordinary talk, people rarely need this word; it belongs to accidents, labs, hospitals, and emergency work.