A tank of diesel fuel at an oil terminal began leaking its contents at around midnight. The fuel had been unloaded from an oil tanker. A total of 100 l leaked out and formed a floating layer on the surface of the stormwater in the tank’s bund (it had been raining heaving since the middle of the night).

Prior to the incident, the order had been given to transfer the diesel from the tanker to the tank up to 461 mm below the tank’s top rim. The tank’s maximum level is set at 400 mm under its top rim. Once the tank was filled, the order was given to blend the diesel in it. As the nitrogen injection facility usually used for this operation was under maintenance, it was decided instead to use a production line to blow air into the tank. Once blending was finished, technicians saw diesel spilling out from under the tank’s dome. The air injected during blending likely caused the diesel to swirl and spill out between the tank’s dome (or roof) and its shell. The tank’s external floating roof had been replaced by a dome. During the change analysis process (Management Of Change, or MOC), the maximum filling level had been set at 400 mm from the tank’s roof. In the MOC, the tank’s filling level had been considered safe.

After the accident, the operator lowered the maximum filling level to 1 m (instead of 40 cm) below the roof’s edge. The alternative blending technique’s role in the incident was not analysed by the operator. The dome turned out to be poorly welded, but the reasons behind this were not investigated. The environmental agency also noted a lack of risk analysis related to ground contamination in the tank’s bund. This matter resulted in another event occurring at the site one month later (ARIA 53164).

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