The present paper describes where sensing and detoxification devices could be installed to get maximum efficiency in an effort to warn and protect citizens against surprise attacks by toxic agents in public buildings. The release of toxic agents may be outdoors, in a single indoor spot or their origin may be diffuse. This work is part of WP3 in the NANOSECURE integrated project supported by the European Union’s Sixth Framework Programme. In indoor spaces people are highly vulnerable to attack from toxic agents introduced by terrorists. Nanosecure aims for maximum public security by developing yet unavailable systems that can be widely deployed for “early warning” and detoxification. Nanotechnology promises sensing and detoxification with far higher efficiency than current methods do. The NANOSECURE project will integrate the technologies into combined protection systems that are intelligent, sensitive, flexible, compact and inexpensive, making them suitable for installation in major situations, e.g. airports, communal buildings, cinemas and theatres. The following dimensions will be described: Time course of pollutant spreading and removal, ventilation rate, ventilation system, operation of windows, space volume, ceiling height, pollutant source characteristic, toxicity of agent, functionality of air cleaners, sensor location and occupant density. This will be based on analysis of the following scenarios: Large airtight space with dominant air change by mechanical ventilation (airport departure terminal), large less airtight space (Central train station), underground space (metro station), very densely populated space (theatre), less densely populated space (sports arena). For sensing and detoxification devices to be effective and preferably ahead of situation, this paper will point out strategic areas where to integrate these devices into the building space and in its immediate surroundings. Examples of deployment of sensing devises may be in exhaust and inlet openings of ventilation systems, in openings as windows and doors and along conveyer belts. The paper will also list typical figures for ventilation rates, air filtration, heat and moisture loads etc in the afore-mentioned scenarios.