The purpose of such quarantine-for-decontamination is to prevent the spread of contamination, and to contain the contamination such that others are not put at risk from a person fleeing a scene where contamination is suspect.
New developments for quarantine include new concepts in quarantine vehicles such as the ambulance bus, mobile hospitals, and lockdown/invacuation (inverse evacuation) procedures, as well as docking stations for an ambulance bus to dock to a facility that's under lockdown.