A storage area that was low value in week 1 may contain expensive plant, cable or equipment later. The site also changes at the end of each shift. Tools are put away, plant is parked and temporary compounds become quiet. That creates a predictable period when an intruder can approach without being challenged by the workforce.
The risk therefore changes with the construction phase and the assets on site. Security needs to account for the perimeter, access routes, storage areas, plant positions and the periods when the site is unoccupied.