Abstract: A system and method are defined for disinfection of the structure, contents and included air in large volume enclosures such as mass transit vehicles, transport containers, warehouses, and retail sales or gathering locations to reduce the risk of transmission of contagious biological agents, particularly bacterial and viral agents. Various embodiments provide effective sanitizing actions accommodating differing local circumstances and obstacles. Safety interlock mechanisms, procedural steps and communications means ensure safe operations around humans and animals. The system includes a method for measuring environmental conditions to ensure a safe re-entry state.