What does the action of overhauling a fire involve?

The action of overhauling a fire primarily involves extinguishing the fire and thoroughly investigating its source. This critical phase occurs after the initial firefighting efforts have been successful in putting out the flames. Overhauling is essential because it ensures that all hot spots and smoldering materials are identified and extinguished to prevent rekindling of the fire. Investigating the source further helps in understanding how the fire started, which is vital for future prevention and safety measures. This process not only protects the area but also assists in gathering valuable information, aiding in any subsequent investigations.

The other options, while important in their own right, do not encompass the full scope of the action involved in overhauling a fire. Setting up a fire watch is a preventative measure taken after the fire is out to ensure safety; testing air quality focuses on assessing the atmosphere for hazards; securing the perimeter pertains to the safety and control of the area surrounding the fire situation. None of these actions directly address the thorough investigation and extinguishing critical to the overhauling process.