Final answer:
Branch lines are the pipes directly connected to sprinkler heads in a fire suppression system, essential for delivering water to extinguish flames during a fire.
Step-by-step explanation:
The type of lines that are directly connected to sprinkler heads in a fire suppression system are called branch lines. These lines are a critical component of the fire sprinkler system, supplying water to the individual sprinkler heads. The branch lines connect to larger pipes called mains, which are in turn connected to the water supply. In the event of a fire, the heat will cause the sprinkler heads to activate, releasing water from the branch lines to extinguish the flames.