The most common and most likely answer to this crossword clue is the 11 letter word KNIFE-EDGES
I've seen this crossword clue in Independent
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Buddy explains!

The straight part
We know that "crucial situations" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crucial situations = knife-edges.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
KNIFE-EDGES noun- A piece of steel sharpened to an acute edge or angle, and resting on a smooth surface, serving as the axis of motion of a pendulum, scale beam, or other piece required to oscillate with the least possible friction.
- A precarious balance that could be upset by a very small force in either direction.