Fire broke out in an isomerization unit at a refinery; the unit was responsible for transforming pentanes and hexanes. The blaze also damaged the benzene saturation unit, which served to convert aromatics into saturated compounds. Mechanical deficiencies on a compressor within the isomerization unit had led to the release of a gaseous mix composed of hydrogen (70%), methane and LPG, which when placed in contact with air ignited immediately. The ensuing flare flame was directed towards the benzene saturation unit, at a distance of 14 m; this unit’s destruction greatly contributed to spreading the fire. The compressor, in operation for 20 years, was being used to recycle and circulate this gaseous mix within the unit; it was running in parallel with another compressor of the same type (not involved in the accident). The compressor’s mechanical failure consisted of a break on the bottom of the shell, which was ejected several metres. Some 3 tonnes of highly flammable gases were emitted through the leak cross-section, and approx. 12 tonnes of gasoline burned during the fire. Both the internal and external emergency plans were instantaneously activated. This accident resulted in no injuries or environmental impact, but was responsible for €3 million in property damage.

The unit’s safety report had analyzed the risk of a jet fire though had not anticipated a possible domino effect on the other units. This report was thus assigned for revision to incorporate the more realistic hypotheses relative to phenomenon kinetics, intervention periods, etc.

As regards the lessons learnt from this incident, the refinery operator planned to replace the 2 horizontally-opposed compressors with simple centrifugal compressors in order to: enhance isomerization unit reliability, modify the locations of fire-fighting posts, improve personnel training and drills during emergency situations, and revise intervention and shutdown procedures for emergency situations.

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