Ok so in the materials.json something like wood has the following.
burn_data
{ "fuel": 1, "smoke": 1, "burn": 0.01, "volume_per_turn": "200 ml" },
{ "fuel": 2, "smoke": 1, "burn": 0.02, "volume_per_turn": "825 ml" },
{ "fuel": 3, "smoke": 1, "burn": 0.03 }
what part of this determines how much time is added to a campfire?