What is a characteristic of branch lines in a sprinkler system?

Branch lines are specifically designed to deliver water from the main piping directly to the sprinkler heads. This function is crucial in ensuring that the sprinkler system can effectively distribute water in the event of a fire. These lines form the last segment in the water distribution network of a sprinkler system, which ultimately means they play a vital role in activating the sprinkler heads when needed.

In contrast, the other options describe roles that do not align with the function of branch lines. While cross mains serve as larger conduits that connect multiple branch lines, branch lines themselves do not supply water to these mains. Storing water for emergency use is typically a function of a tank or reservoir within a fire suppression system, not the branch lines. Lastly, branch lines do not connect to the fire hydrant system, as that is a separate infrastructure meant for firefighting by external services rather than for automated sprinkler activation.