"In case of a fire" or "in the case of a fire" both also read to me not as precautions but actions to take after the fire has actually been spotted.
Absolutely! Sorry, reading back I realise I wasn't especially clear, and perhaps also mistook the main question posed by the OP.
In the UK, '(just) in case...' and 'in the case of...' are two distinct phrases, with very different meanings.
1) '(just) in case...' to take a precaution/prepare (
before something might happen).
Using the 'just' makes it sound, while still possible, less likely.
e.g. I'll take an umbrella in case it rains.
e.g. Take a camera with you just in case you see something worth taking a picture of.
This is a common expression here in England.
2) 'in the case of...' means the same as 'in the event of...' I believe it's used to explain what will/could/should/must/might be done in a certain situation.
I don't think it's very common. It sounds rather formal and more like something that would be written rather than spoken.
e.g. In the case of the game being drawn at the end of 90 minutes, extra time will be played.
e.g. (Using the OP's original example) In the case of a fire, you should dial 911.
This second example certainly seems possible, but we usually see 'in the event of a fire...' in this sentence in hotels etc.
Hope that's a bit clearer, from an Englishman's perspective!
