Final answer:
It is safest to approach a fire with a portable fire extinguisher from a position that is against the wind to avoid having the fire-driven towards you.
Step-by-step explanation:
When operating a portable fire extinguisher, it is safest to approach the fire against the wind. This is because approaching from the leeward (downwind) side can cause the fire to be driven towards you by the wind, making it more difficult and dangerous to fight the fire. Moreover, as fires burn more intensely uphill especially if driven by wind, it's better to approach from an uphill or level direction, if possible, for safety.