in the context of C/AS a private deck leading to DEOP may be required to be a building element that requires a FRR but not a fire separation due to the definition of a fire separation. in my view, and i realise it might not be a popular one, is that the only part of C/AS1 that could be enacted in this scenario is paragraph 5.5, carports or similar construction, if you consider a deck to be a similar construction? you could try and shoehorn it into paragraph 4.1 but this approach falls flat when you look at the definitions, escape route/ occupied space/open path etc… common sense says that a balcony is not in or within a building, its outside, and the normal and natural meaning of within is to be inside something.
4.13.1 C/AS2 only requires fire rating of intermediate floors within the firecell so fire rating is not required for external floors such as balconies. However in some cases of large balconies with a fire risk below it may be prudent to fire rate the balcony to protect escaping occupants. Sometime you just have to use your judgement.