In addition to the data collected for the elaboration of computing probabilistic models, experiments were carried out with lightning and video equipment. The recorded images show the patterns of air streams in interaction with the buildings. They recall the first photographic records of air-dynamics realized at the benign of the XX century by Etienne Jules Marey. But now, transported to urban dimensions, those images acquire the consistency of cartography, depicting in time and space the behaviour of airflows in relation to the city structure. The empirical questions of these visual trials are apparently very simple – in the case a hazardous is released in the atmosphere, how does it behave? Where it would blow? Which routes does it follow? How does the form of the urban fabric interfere in its mode of dispersion? And more importantly, what are the areas that are potentially safer and the ones that offer greater risk? Atmospheric mappings produced under controlled laboratorial conditions are necessary to inform risk-reduction designs and emergency-response planning. The air-dynamic cartographies constitute a set of tools based on which an “exceptional planning” is drafted out: public spaces are converted into isolated areas, streets are blocked and traffic diverted, underground stations are evacuated, air-conditioned office buildings become atmospheric shelters… That re-urban planning is always a potential, only actualized in extraordinary situations and for a short period of time. Yet it is no less sophisticated than an ordinary urban design, for it must be sufficiently elaborated to allow the fast and efficient reconfiguration of the urban dynamics.