Safety lessons and reflections following incinerator vent commissioning in a chemical plant; a case study of a complex socio-technical system

•We describe incidents that occurred during commissioning of a vent header.•Fatal design flaws may show up during commissioning.•Commissioning is a highly interactive and social task requiring a coherent team.•Operators may be an important source of information into the behavior of a plant.

In a bulk chemical plant producing resins, a flashback from an incinerator through the vent system into the reactor hall occurred during commissioning of a newly installed vent header system. The original design of the vent header system was seriously flawed not being in line with current practice. Subsequently the vent header was re-designed into a rich/lean vent header system. This paper explores the reasons behind a number of incidents and near misses that occurred during both the commissioning of a vent header system and its recommissioning following system re-design. Furthermore, it reflects on some broader implications for approaches to safety around what can be recognised as complex socio-technical systems.