Fire was a constant companion in medieval life. Almost every building had a fire burning, and entire towns and cities were regularly destroyed by fires that got out of control.
In this mod, villagers sometimes start accidental fires in their houses, at work or in churches. Fires will destroy building parts, trees, crops, and if you are using those mods, rubbish and stumps as well. Fires will spread to other objects within 5 metres, and eventually burn a circular area of about 20 metres in diameter. Fires won't start until you have at least 30 villagers.
When a fire starts, any Builders within 75 metres will be called on to fight the fire. They will go to a nearby well to get water in buckets, then dump the water on the fire. If the Builders arrive in time, they can put out the fire before it spreads or destroys anything. After the fire is put out or has burned itself out, Builders will return to their normal jobs. You can improve your settlement's fire-fighting ability by employing plenty of builders and having wells close by.
To help prevent fires from getting out of control, build Fire Watchtowers. When manned by a Fire Watch, these towers give you extra time to fight the fire before it spreads. Fire Watchtowers have an effective radius of 75 metres. With a Fire Watchtower, Builders and a Well nearby, it's likely that a fire will be stopped before it damages anything. Watchtowers unlock at 25 villagers.
An optional upgrade to the Watchtowers is a Fire Brigade, which must be snapped onto the tower. This provides for 3 full-time fire fighters to help the Builders contain any blaze.
You can start fires on purpose. These are useful for clearing away trees for farms, or for the fun of seeing a building or woodland burn down. Set more than one fire so that the Builders don't put out intentional fires too quickly.
Watchtowers and the part for starting fires are in the Service menu.
RaisinMuffin for the Fire particle and textures
Minotorious for teaching me how to use behaviour trees