Final answer:
After a fire is extinguished, the Fire Department Chief or their representative has the authority to close the control valve, ensuring the safety of the environment.
Step-by-step explanation:
If a fire has been completely extinguished, the Fire Department Chief or their representative may close the control valve. Once a fire is confirmed to be out, it is important that trained professionals from the fire department evaluate the situation. They will ensure that the environment is safe and that there's no risk of the fire reigniting before taking steps such as closing the control valve, which stops the flow of water from the sprinkler system or other firefighting systems. The process must be done carefully to prevent any further hazard or damage.