In a water treatment plant, a 5 m³ leak of 96% sulphuric acid (H2SO4) occurred on a flange joint on the outlet of a 28 m³ tank temporarily installed while work was carried out. This rented storage capacity situated outside was not protected from bad weather. The level sensor in the retention tank detected 30 cm of acid and triggered the ‘acid retention’ alarm. The drinking water production installations were secured: isolation of the electrical cabinet of the acid storage tank. Absorbent booms were set up, but the available resources were not sufficient to contain the leak.
The presence of 400 l of rainwater in the retention tank caused an exothermic reaction and corrosion of the 30 m³ tank’s lining. As this retention tank was no longer leaktight, some of the acid poured onto the floor. The weekly inspection on 26/08 had not detected these non-conformities on the retention tank.
Fire-fighters and a chemical emergency squad went on site. A safety perimeter was set up around the site. After protecting the stormwater networks, earth dams were built to contain the acid flow. An external company pumped out the substance and drained the tank. The pumping was delayed due to the heating of the tank walls (70 °C). At the external company’s request, a preventive cooling device for the tank was installed to protect against an excessive rise in temperature. Two members of the chemical emergency squad wearing protective suits unblocked the valve, which allowed the substance to be drained into another storage capacity. The leak was situated on a flange joint on the drain valve of the storage tank. The incident led to the presence of rain water and a leak along the joint. Sand was spread over the areas polluted with acid. The contaminated soils were removed.
The operator decided to stop using this sulphuric acid tank. It chose to construct a buried concrete retention tank with a leaktight stainless steel liner to prevent any corrosion by acid, rather than use a resin lining. The damaged installation was dismantled. The new installation will include an H2SO4 metering and storage station.
