Starting in September 2004, several months after a company specializing in the treatment of liquid and solid waste had set up operations in the Ormoy Business Park (ZAC) in Essonne, employees of nearby businesses began complaining of chemical odors followed by symptoms of irritation. In June 2007, the severity of the health situation led the management of one of the companies to temporarily relocate its employees outside the ZAC. The survey conducted among four companies in the ZAC and nearby residents revealed symptoms common to the majority of people, including irritation of the mucous membranes and skin, as well as general symptoms, with a very high incidence in two companies. The site visit and analysis of environmental surveys conducted elsewhere indicate the presence of emissions into the atmosphere and the wastewater system, which explain the odors perceived. The results of analyses of several chemical compounds conducted over a two-week period do not show any exceedances of the threshold values at the perimeter of the polluting plant, though they do not rule out the possibility of sporadic concentrations reaching irritating levels. The two-year shutdown of the ventilation system and design flaws observed in the premises of the company most affected by the symptoms were likely a contributing factor to the onset of symptoms, although these persisted even after the issues were corrected. The results of the investigation conducted by the Cire show that, in addition to the environmental component (outdoor and indoor air quality), a collective psychological component likely explains the widespread nature of these symptoms. This event is consistent with chemical odor intolerance syndromes. The duration and levels of exposure among employees and nearby residents do not raise concerns about the onset of long-term health problems. (R.A.)