The Sensitive (S) location class doesn’t seem to cause much confusion (with one minor exception).
Its intent is obvious: to identify locations where there are people who are less able to protect themselves against a pipeline failure. This includes particularly pre-schools, schools, hospitals, aged care facilities, etc. Prisons are are another instance – the inmates may be able-bodied but are nevertheless limited in their movement for other reasons. (But every case has to be considered on its merits – I know of an old 19th century gaol whose massive 6 m high stone walls provide superb radiation protection for anyone inside!)
AS 2885 requires that Sensitive areas be treated the same as T2 (High Density) areas. So if your rural pipeline passes by a little isolated country school then the section of pipeline within the measurement length from the school must be designed the same as if it is in a densely populated urban area.
Nothing complicated about that I think.
However confusion sometimes arises because of this statement at the end of the description of Sensitive location class in AS 2885:
It shall also include locations of high environmental sensitivity.
The key to correct interpretation of this is that the safety management study process in AS 2885 is about failure of pipelines while in service. It has nothing whatsoever to do with construction impacts – they are important, but are addressed through different processes. A better form of words might have been:
It shall also include locations of high environmental sensitivity to pipeline failure.
With that clarification, it should be apparent that gas pipelines will rarely if ever receive an S classification for environmental reasons (I’ve certainly never encountered one). However it may be entirely reasonable for an oil pipeline to have a number of Sensitive locations, depending on where spilled oil may spread and the environmental damage that could result.