In a chemical plant, during an inspection at 6:45 am, a plant technician detected a 33% leak of hydrochloric acid (HCl), generating a small white cloud at the lowest point of a storage tank. With a capacity of 100 m³, the ebonite-lined steel tank was filled to 80% and positioned close to a second similar tank, in a 150-m³ retention basin.
The site IOP was activated and the internal emergency services intervened to immerse the leak; four water jets at 2.5 bar were used. The transfer of acid to the second storage tank was started and the effluent was diverted to the plant’s event basin.
At 7:30 am, a second leak broke out on the 15-cm diameter, lateral HDPE pipe supporting the manometer for pressure level measurements. The large opaque white cloud that generated was visible outside the factory. The upper level IOP was activated, and the fire department was alerted; fire-fighters arrived onsite at 7:40 am but no intervention was required. Adjacent traffic lanes were closed off and reopened at 8:45 am. The internal emergency staff, wearing acid-proof suits, managed to close a control valve and stop the leak at 8:15 am.
Complete emptying of the storage tank to the backup tank and tanker lorries ended at 5 pm, while the retention basin was emptied by 7 pm. The 2,000-m³ acid effluent generated and recovered in the event basin was to be neutralised with sodium hydroxide before discharge into the environment after compliance verification. The operator and Prefecture communicated on the spot about the event.
The discharge was modelled after the accident and revealed that 5 m³ of acid had been discharged at an average flow rate of 1.54 kg/s for 45 min. The area considered to have been subjected to irreversible health effects was limited to 20 m from the leak point. Samples collected in the neighbourhood by external fire-fighters did not indicate any risk to the population at large in the immediate vicinity of the site, though great anxiety was felt by the population upon seeing the white cloud released.
An investigation was conducted to determine the causes of the accident; the first leak resulted from degradation of the ebonite lining in the storage tank at the leak point, which caused corrosion of the steel by the acid. The second leak was due to rupture of the manometer pipe from the indirect power of a hose jet set up during the emergency intervention.
In compliance with feedback experience, the onsite HCl storage was to be limited: the two 100-m³ tanks were to be replaced by a single storage capacity of 50 m³ in PE on 15th October, 2007. Moreover, all onsite storage tanks were inspected in order to detect any poorly-fitted equipment, e.g. the manometer on the pipe that caused the second leak.