Process units should have staggered access from at least two directions. The space between battery limits of adjoining units should be kept clear and open. Do not consider the clear area between units as a future area for process expansion. It should be labeled on the drawing as ‘Clear separation space not for expansion use'.

To prevent a single event from impairing the overall operation, equipment or structures common to multiple process units, such as large compressors and turbines, and central control rooms should be located carefully. (It should be based on hazard analysis and evaluation. Also refer to API RP 752 on ‘Management of Hazards Associated with Location of Process Plant Buildings' for more details). Layout the equipment within a unit in one of two general ways:

• Use grouped layout, where similar equipment is grouped together to ease operation, maintenance and control.

• Use flow line layout, where equipment is arranged in sequence similar to the PFD.

Where ever it does not conflict with loss of control, consider accessibility for maintenance and operations in determining spacing and layout. Locate equipment needing frequent overhaul, maintenance or cleaning at unit boundaries. Locate large vessels or equipment close to unit boundaries to allow easy access of cranes.