Right at the beginning of the story, you get a torch, which is one of the most important tools againts infected animals.
(Thanks to IDALGAME for the nice model)
It can be used in many different ways...
Standing Torch
When you light up a standing torch, the fire creates a safe place. Infected animals will not dare to get closer to the fire.
Oil
In some areas there are old and broken oil barrels, The content is spread on the ground in form of oil puddles. Light it up and the fire spreads until the whole puddle is burning. This can create you a safe passage in dangerous places.
Dry Plants
Dry plants are highly flammable. When you burn them to ashes, new passages can open.