Question

To extinguish a fire with a portable extinguisher, a person must:

Answer 1

know how to use the extinguisher and have access to it right then and there or have it nearby

Answer 2

have immediate access to the extinguisher, know how to actuate the unit, and know how to apply the agent effectively. Attempting to extinguish even a small fire carries some risk. Hopefully this is what you were looking for.