What's a dangling particle? Do you mean dangling participle, as in a dangling modifier? Or maybe a particle used similarly?

See these links:
https://owl.english.purdue.edu/owl/resource/597/1/
https://en.wikipedia.org/wiki/Dangling_modifier

Be aware though that "dangling" is a matter of style rather than syntax in the strict sense of linguistic research. So there may not be an exact/consistent answer for it.

In short, a dangling modifier is one that is far away from the thing it modifies:

Standing in the room, I saw him over there.
If he is the one standing in the room, that is dangling, because it is too far removed.

But since it's a question of style (and not necessarily an error or really a grammatical problem, just potentially confusing!), "identifying" them is just a matter of judgment.