A fire broke out on the vacuum distillation unit in a refinery during its scheduled five-year shutdown. This unit essentially consists of a distillation tower loaded with the heavy fraction from the atmospheric distillation, and a gas-fired furnace on the upstream portion also able to burn incondensable materials from the tower head.

The unit had been restarted the day before following the acceptance of the work, while other job sites were still underway at the site. The reheating operation had begun during the night, and the unit was still in the power build-up phase. At around 9.15 am, thick black smoke was observed coming from the stack (fire in the furnace), with flames shooting from the open explosion vents. This situation was preceded by hammering in the pipes and rising pressure in the tower increase and the opening of valves: hydrocarbons began spilling outside. The accident was surrounded by site crews after performing the following operations: injection of steam into the furnace, injection of nitrogen into the tower, isolation of the units, application of foam around the base of the unit. No one was injured. The effects of the accident was limited to the release of dusts and hydrocarbons around the tower and on in a small portion of the neighbouring installation, the rupture of a steam pipe. The personnel from external companies (1,000) working on the site were evacuated, although activity was resumed rapidly.

Following the inquiry, it appears that erroneous level indicators caused the tower to be overfilled then the backflow of liquid into the furnace via the vacuum system (backflow of incondensable materials). A brief summary of the findings: the local levels were not visible, the chain associated with the control levels in the bottom of the tower had not been completely checked (card), and the configuration of the system and notably the extraction levels were not correct.

An emergency shutdown order was issued requiring the operator to submit a detailed report of the accident’s causes prior to the restart of the installation. Following the examination of all elements submitted and an on-site inspection, the Classified Installations Inspectorate was no longer opposed to the resumption of operations (04/30/2002). The measures foreseen by the operator include: an operator dedicated to instrumentation on site on permanent basis, selection of a standard configuration for restart, followed by the material assessment, monitoring by an operator.