Final answer:
Potassium bicarbonate (PKP) portable extinguishers are primarily intended for use on Class B fires, which involve flammable liquids, and can also be used on Class C fires involving electrical equipment.
Step-by-step explanation:
A potassium bicarbonate (PKP) portable extinguisher is intended for use primarily on Class B fires. Class B fires are those that involve flammable or combustible liquids like gasoline, kerosene, grease, and oil.
Potassium bicarbonate extinguishers are effective because they work by interfering with the chemical reaction that takes place during the combustion process. This type of extinguisher can also be used on Class C fires, which involve electrical equipment, as the agent is non-conductive and does not leave a corrosive residue which would further damage the electrical appliances.