Establish zones for the incident.
The Hot Zone will contain the spill and any area affected by fuel runoff. Any area on fire, area where flammable vapors are present AND area expected to be affected by radiant heat or explosion is also included in this zone. Firefighters will be working in the Hot Zone during fire suppression but apparatus should be positioned in the Warm or Cold Zone.

Zones should be known by all and should change if needed.

It is difficult for all personnel grasp the same imaginary line. Use defined barriers if possible.... highway lines, signs, guardrails, or anything which is easy to describe to others.
Expand the higher danger zone into the lesser if need be.

There is no single answer for setting zones except for assuring that
life safety is the #1 priority

Zones will rarely be perfect circles.
The Hot Zone may be elongated to mactch a wind direction and speed.
Irregular shapes may be needed to account for flowing or potentially flowing fuel.

Example:
The fill points for fuel delivery trucks at this location are loacted at the South portion of the parking lot.
Leaking fuel would flow downhill, around the curb, into a drain which runs uder the road and into a ditch beside of Athen's Pizza.

A situationally aware firefighter/commander should be looking at the topography and for drains & ditches.... anywhere the fuel spill will flow to.