What is the first step in the procedure for re-chlorinating a full 400-gallon water trailer?

The correct course of action when re-chlorinating a full 400-gallon water trailer begins with accurately measuring the appropriate amount of chlorine to use. This ensures that the chlorine concentration is adequate for effective disinfection.

Option C emphasizes the precise preparation of chlorine, specifically calcium hypochlorite, which involves creating a solution from the prescribed amount. This step is critical because it allows for proper mixing and distribution of the chlorine throughout the water in the tank. By using a measured amount in half-gram spoonfuls and mixing it with water, you ensure a controlled dose that can effectively eradicate pathogens without introducing excessive chlorine, which could be harmful or unpleasant.

Using a precise method of preparing the chlorine solution is essential in sanitation protocols to ensure both safety and compliance with health regulations. Proper dilution and mixing fosters even distribution of chlorine in the 400-gallon tank, promoting effective disinfection while minimizing any residual effects that could alter water quality.

While other options might seem like possible steps in the process, they do not adequately ensure the proper concentration or mixing necessary for effective sanitation. For instance, some methods may risk uneven distribution of chlorine or not take into account the correct water treatment practices, which could compromise the effort to achieve safe drinking water conditions.