Operationally managing that situation boils down to balancing the benefits and drawbacks of doing a fix on the run versus shutting the process down to effect a permanent repair.
The key message about any change, whether technical or organisational, is to have a process, and assess the impact and consider everything. The change needs to be managed appropriately, considered in terms of its impact in design codes and standards, and in procedures and people and company training. This applies whether the fix is permanent or temporary.
Managers must know both the normal operational backups and the emergency ones. And that fundamentally boils down to robust emergency response plans, emergency scenarios or critical response scenarios.
As I was coming into industry, one of the incidents that was relatively fresh was Flixborough, an explosion at a chemical plant in north Lincolnshire that killed 28 and seriously injured 36. It was caused by a temporary change; there were other technical aspects, but robust change management was not followed. There was also a lack of engineering authority in the organisation due to restructuring. And emergency plans and response procedures didn’t properly consider what mitigation measures were needed.
Next June marks 50 years since the incident, and by now every person involved has most likely since retired. To prevent organisational knowledge from fading, it’s important to include detail from real-life scenarios in staff training courses. (I recommend Incidents that Define Process Safety, ISBN 978-0470122044, published by Wiley and the American Institute of Chemical Engineers, which profiles 50 industrial incidents.) Referring to real events makes procedures, processes and practices real – not just bits of paper that workers are obliged to follow.