if you think the plant manager should be exonerated because he folowed the rules, you are siding with deontology, whereas if you think he should be punished because a death occurred under his supervision, you are siding with consequentialism
This is missing the point. Consequentialism is about making decisions, not about judging past decisions. Consequentialism says that if punishing the manager would (in expectation) have better consequences than not punishing them, then they should be punished, and otherwise they shouldn’t. Deontology says that if the rules say to punish the manager, they should be punished, and if the rules say not to punish the manager, they shouldn’t be punished.
This is missing the point. Consequentialism is about making decisions, not about judging past decisions. Consequentialism says that if punishing the manager would (in expectation) have better consequences than not punishing them, then they should be punished, and otherwise they shouldn’t. Deontology says that if the rules say to punish the manager, they should be punished, and if the rules say not to punish the manager, they shouldn’t be punished.