A fire broke out at 8:15 pm in a vacuum distillation unit at a refinery. Internal and external first responders had the blaze under control within 90 minutes. Two slight injuries were reported: a technician suffered first-degree burns and a fire-fighter sprained his ankle, but both were able to return to work the same day. The environmental impact was limited to a black, non-toxic smoke cloud. Property damage was considerable, and the unit had to be shut down an estimated 3 months to allow for inspections and repair work.

This fire resulted from an ignited leak of slop wax (a paraffin residue) subsequent to an opening of approx. 40 cm² (10 cm*4 cm) on the 3″ line for recycling this product into the vacuum distillation unit load. The slop wax drawn from the riser at 370 °C, which is higher than its self-ignition temperature (220°-300°C), instantaneously combusted when placed in contact with air.

Several causes acting together were responsible for this accident. For starters, the presence of sulphur in the slop wax (0.7%-1.4% S) and the racking at 370°C generated a high-temperature sulphurous type of corrosion that in turn produced a loss of pipeline thickness on the order of 1 to 2 mm. Moreover, the targeted portion of the circuit had been added during a facility modification performed in 1988, which was intended to inject slop wax into the unit load: this modification used 3″ carbon steel, a material that was not adapted to either the temperature conditions or the product composition. The defective pipeline was not included in the “slop wax” inspection programme, but instead as part of the programme dedicated to the load circuit, which is less vulnerable to corrosion. Since 1988 therefore, the thickness of this part of the circuit had been less frequently inspected than that of the “slop wax” circuit. The operator commented that during the fire outbreak, 3 automated sectional valves out of the 7 were not working properly and had remained open or partially open. Also, some electric pumps and turbines that had not been equipped with remote controls could not be shut down when the fire first broke out.

Following this accident, the operator revised the site’s inspection schedules, particularly for pipelines whose service temperatures exceeded the product self-ignition temperatures. An audit and update were ordered of the plant’s inspection plans to ensure compliance with a stricter set of criteria. The operator sought to verify that all previous modifications had been taken into account in the updated inspection plans and moreover that modification procedures addressed corrosion at the level of specification change zones. A systematic alarm and safety testing protocol at regular intervals was adopted in addition to checking that the shutdown controls for all rotating machinery were accessible remotely. As a final consideration, the operator introduced an adequate and continuous training programme on incident handling strategies for operating personne