As part of a campaign to measure pesticide levels in ambient air conducted in August 2007 by the French Agency for Environmental and Occupational Health Safety (Afsset) in three schools in the municipality of Chenôve (21300), abnormally high levels of wood-preservative compounds (such as lindane) were detected in several classrooms at the Bourdenières Elementary School. This campaign was carried out following Afsset’s analysis of pesticide measurements in outdoor and indoor air, conducted in August 2006 by the accredited air quality monitoring association of the Burgundy region. Indeed, high levels of several compounds in the hexachlorocyclohexane family, notably lindane, had been measured in a classroom. The follow-up measurement campaign conducted in 2007, at the request of Afsset, confirmed these initial findings. Furthermore, it revealed contamination of dust and furniture. Sampling of building materials identified the ceiling support structure as the primary source of emissions. Given the toxicity of these compounds, the vulnerability of the affected population, and an initial risk assessment, Afsset alerted its overseeing ministries on September 6, 2007. The risks of acute poisoning associated with these compounds were quickly ruled out for the children and staff attending this school. However, the health authority deemed it necessary to assess the potential health risks associated with chronic exposure of users of the Bourdenières school complex (elementary school and preschool, whose building shares the same construction characteristics) and, to that end, to complete environmental investigations at the school. In this context, at the request of the Ministry of Health, the Prefect of the Burgundy region and the Mayor of Chenôve decided to close the entire Bourdenières school complex on September 17, 2007. At the same time, following a proposal by the French Institute for Public Health Surveillance (InVS) and the French Agency for Safety, Health and Environment (Afsset), a mechanism for collective expert assessment and situation management was established to respond to the health authority’s request. (R.A.)