Oil refineries are incredibly complex pieces of machinery.
I’ve read the technical report at the now-Cenovus, formerly Husky Superior refinery that occurred in 2018 (this was before Cenovus took over Husky).
If you ever want to get a sense of appreciation at the technological marvel of oil refining, you should read this report.
This refinery is currently being rebuilt and should become operational again sometime this year.
Cenovus has had bad luck with their refineries. About a month after they signed a deal to acquire the remaining 50% of their Toledo refinery (the other 50% is owned by BP and the refinery is operated by BP), the refinery blew up on September 20, 2022 which resulted in the death of two workers. Thankfully for Cenovus, it was before the deal actually closed, and one would presume that the acquisition contact would require the refinery to be in a non-blown up state before the deal closes.
The preliminary report, released on October 31, 2022, indicates that a release of flammable materials from a specific drum was the origin of the fire.
These investigations take a lot of time and I do not think the repair job will be a speedy process either. It is too bad for Cenovus, as refinery spreads are sky-high at the moment and considering the lack of capacity expansion on downstream operations, will likely be this way for some time.