At around 9:30 a.m., a drip leak of butyric acid (corrosive) occurred on a pipe between the unloading area and storage tank of an upper-tier Seveso chemical plant during a pumping operation. Both areas were surrounded by a retention system. The operator halted pumping and purged the line with nitrogen. The leak grew, spreading to the structures and a portion of the plant’s roads. The operator immediately halted purging. Butyric acid has an odour-detection threshold of 0.001 ppm. Because of its pungent and foul-smelling odour, the plant’s first responders donned self contained breathing apparatus (SCBAs) and spread potassium carbonate (an absorbent) on the ground. The operator considered that spraying the area would cause the odour to persist. The product absorbed by the potassium carbonate was collected into drums and set aside for disposal. At around 10:00 a.m., the town hall told the operator there were reports of the odour throughout town. A nearby resident also complained about the smell. The alert was lifted at 10:43 a.m. The operator washed the acid-covered structures with water until late that afternoon, when the odours finally disappeared. The wash water was deviated to a retention pond.

A total of 50 l of acid was spilt. There was no increase in the TOC level at the aqueous discharge outlet. The odour was perceptible in town until late afternoon.

The operator dismantled the line to look for the source of leak. He found a Viton seal that was completely damaged. Dripping during pumping combined with purging of the line and the associated pressure caused the seal of the flange assembly to come out of the pipe.

The operator checked the entire line and found other seals in the same condition. The damage to the seals was caused by other substances pumped through the line (it is not used exclusively for butyric acid).

The operator replaced the defective seals with Teflon-coated seals. The operator plans to carry out compatibility tests with the pipe’s materials when developing new products.