An employee at an aluminium section plant complained of suffering from gastroenteritis. Two days later, he was hospitalised and 6 days after that, the hospital ward manager diagnosed contamination by Legionnaire’s Disease. Questioned by phone by the Inspection Authorities for Classified Facilities, the plant operator announced that no cooling circuit in use was spraying cool water on airflows whether for industrial applications or air conditioning of premises. Since no other case of the disease was diagnosed, the operator suspected a cause external to the company but still proceeded with sampling at 7 points of the plant’s water circuits, including the shower used by the contaminated person (recent facilities used very frequently since they were shared by all on-duty personnel).