In the boiler room of a synthetic fibre plant, the partial failure of a primary circuit drainage pipe caused a leak of liquid coolant composed of 73.5% phenyl oxide and 26.5% diphenyl. Liquid spread over the ground and then vaporized: a large cloud of coolant vapour (vaporization at 255°C) quickly engulfed the room, tripping the optical detection smoke alarm and escaping via roof openings. The emergency information procedure and internal emergency plan were both activated. An intoxicated employee was hospitalised for 1 hour. The plant operator decided to drain the boiler room circuits into tanks dedicated for this purpose; 4.5 m³ of fluid were recovered in the 70-m³ boiler room tank retention pit and pumped by an external firm for incineration. Vaporized product around the leak and tank vent (500 litres), during circuit bleeding, were dispersed into the atmosphere before partially condensing again in contact with structures outside the building. The operator also noted the presence of coolant in a sewer collector pipe. Fire-fighters installed a plug in the wastewater collector and recovered this coolant using absorbing agents. Samples taken of the water table, in the collector pipe and around the treatment plant were tested for diphenyl and diphenyl oxide: the concentrations measured were very weak. The Sanitary and Social Affairs Office checked with a local hospital to ensure no one fell ill due to the cloud. The facility was closed for 24 hours, after which the installations and utilities were gradually brought back online.