At a chemical plant, a styrene tank “imploded” causing the release of approx. 3 tonnes of styrene product. On the day of the accident, the (44-m³) tank was being filled via a tanker truck when the driver noticed that the gas return running from the tank on the cistern was closed. He decided to fully open the corresponding valve: the tank literally imploded and 3 tonnes of product were discharged, yet this quantity could be recovered in the retention basin (capacity: 80 m³). The emergency plan was activated: fire-fighters were notified and site personnel evacuated. The tank was destroyed and the site shut down for 2½ days. This event was caused by a sudden rebalancing of pressures between the truck cistern, held in low pressure, and the over-pressurised tank. The ensuing “suction” phenomenon led to tank failure.