According to the 2021 International Plumbing Code, what are the required concentrations of free chlorine when disinfecting a new building's domestic water system?

The correct answer is based on the guidelines provided in the 2021 International Plumbing Code, which sets standards for disinfecting domestic water systems. When disinfecting a new building's water system, it's essential to achieve the right concentration of free chlorine to effectively eliminate potential pathogens like Legionella and ensure the water system is safe for use.

Option B specifies a concentration of 50 ppm of free chlorine maintained for 24 hours or 200 ppm for 3 hours. This option is correct because it falls within the recommended standards for disinfection processes in plumbing systems. Maintaining proper chlorine levels is crucial for effective sanitation, and the durations given in this option are also established to ensure that any residual pathogens are adequately killed, promoting a safe environment for building occupants.

In contrast, the other options present different concentrations and exposure times that do not align with the accepted directives stated in the plumbing code. For instance, concentrations that are too high for a short duration may not allow for complete contact time necessary to effectively disinfect, while lower concentrations for extended periods might not achieve the necessary pathogen level reduction. Option B appropriately balances concentration and duration, effectively ensuring both efficacy and safety in the disinfection process.