According to TADS, what should be done after aiming at the base of the fire?

When using a fire extinguisher, particularly in accordance with TADS (Tactical and Strategic Firefighting Guidelines), after properly aiming at the base of the fire, the next step is to depress the thumb lever. This action allows the extinguishing agent to be released in a controlled manner, effectively targeting the flames where they are located and maximizing the chances of successfully putting the fire out.

The reason this step is crucial is that direct contact with the fuel source is necessary to eliminate the fire. Aiming at the base ensures that the agent impacts the most combustible parts of the fire. Once the extinguisher is aimed appropriately, pressing the thumb lever allows for the necessary discharge of the agent, creating a barrier and cooling effect that combats the flames.

The other options would not follow the correct operational procedure for using a fire extinguisher effectively. Withdrawing the extinguisher or turning it upside down would disrupt the firefighting effort, while setting it on the floor would prevent immediate use and could hinder the fire suppression process.