In Dying Light 2, the hero needs to get to the Central Loop to find his sister. But the tunnels have been blocked off by the Peacekeepers, due to the murder of their commander Lucas.
In the Only Way Out quest, the hero needs to enter the metro tunnels from the other side of town far away from Quarry End to get to the Peacekeepers to ask them to open the tunnels to the Central Loop. At the safehouse above the metro tunnels entrance, the hero looks below at the entrance to the metro tunnels and finds it blocked off by quite a small hoard of zombies. The hero must find ways or combat tactics to defeat these zombies, as it is one versus many.
The hero uses the distraction tactics initially.
Then the hero finds the zombies are too sound sensitive to be distracted by the coins alone. And then there are these canisters near to the entrance. So the hero decides to use them.