Final answer:
Potassium bicarbonate (PKP) portable extinguishers are primarily intended for Class B and Class C fires, including those involving flammable liquids and electrical equipment, but not suitable for metal fires such as those involving magnesium.
Step-by-step explanation:
A potassium bicarbonate (PKP) portable extinguisher is primarily intended for use on Class B fires, which involve flammable liquids such as gasoline, oil, and grease, and also Class C fires that involve energized electrical equipment. Potassium bicarbonate, when deployed in a fire scenario, works by releasing carbon dioxide and potassium carbonate. These substances help to smother the fire, interrupting the chemical reaction and cooling down the burning material. CO₂ fire extinguishers, however, are not suitable for certain types of metal fires, such as magnesium, as exemplified by the reaction 2Mg(s) + CO₂(g) → 2MgO(s) + C(s), where the carbon dioxide does not effectively put out the magnesium fire.