The standards apply under all conditions. I suggest that you read them very carefully. There is no requirement to post anything that is inaccessible. If access to an area is restricted such that personnel are prohibited entry into an area, there is no requirement to survey or post that area.
So, if part of your plant yard is a newly-created High Radiation Area, but nobody has access to that part of the yard, there is no requirement to go out and rope it off-or even to survey it for that matter.
Under most scenarios that I have run in my career, during the "accident" the entrance to the plant is locked, posted as a LHRA, and continuous RP escort is required for entry. During the recovery phase (when conditions are stabilized) the survey teams establish the postings working their way in from the site boundary.