I've been looking into fire spreading in 5e and have not seen many things that have all the details I'm looking for. Several times now in my campaign a building has been set on fire and I'm tired of not having set rules for what exactly happens. This only applies to buildings that are flammable (wood floors/walls/ceilings). If I say object I'm talking about the location the fire is currently.
Fire spreading has 4 phases
|Level||Damage||Ability to Spread||Object HP|
|1st. Smoldering||1d4||No||85% or greater|
|2nd. Growing||1d6||Yes||Between 85% and 64%|
|3rd. Burning||1d8||Yes||Between 65% and 45%|
|4th. Decaying||1d4||Yes (only down)||Less than 45%|
Object hp refers to the objects total hp.
Health of object:
This is up to the dm to decide. Normal wood flooring would be resistant so around 20 hp according to RAW. Flooring of walls of a hovel at the edge of a small camp would not be resistant so it would only have about 4 hp. Examples of hp%. 20hp floor, 1st level is down to 17, at 16 it becomes level 2, then at 12 it becomes level 3, at 9hp it becomes level 4.
Any spell that states "ignites any flammable objects in the area that aren't being worn or carried" or something similar, will set the squares in the area affected by the spell on fire at 1st level. Attempts to light fire with tinderbox, torches, etc will also start a fire at level 1. If you are physically starting the fire (torch, tinderbox, etc.) you must be in that square to start it (It would be wise to move out of said square after the fire is lit, if they do not move out they take that fire levels damage at the end of their turn). Using an accelerants (oils, alcohol, etc.) to start a fire will start it at level 2. Torches and accelerants can be thrown.
Each square of fire gets its own turn. On its turn roll for damage depending on the size of the fire, this damage applies to both creatures and burnable objects on this square. Then, if the fire is able to spread roll a d20 on a roll of 1-8 the fire spreads in a direction. In this diagram the fire is location on the number 9.
Using 2 as North is a good way to keep the direction the fire can spread. On a 9 the fire increases its level by 1 up to a maximum level of 3. If the fire is level 3 and the ceiling/floor above the square is 10 ft. or less, it lights the floor/ceiling above on fire. If the fire is level 4 and is on ceiling and/or has a floor below it the square below is set on fire, up to a maximum of 20ft distance between the floors. On a 10 – 19 the fire continues to burn without spreading. On a 20 the fire expands to 2 random directions. Roll 2 d8 and the fire spreads to both those locations (if the numbers are the same that fire starts at level 2). A floor next to a wall is able to spread to the wall and a wall next to a ceiling or floor is able to spread to it.
If a fire tries to expand to a square that already has fire on it, the fire being expanded to increases its level by one up to a maximum of 3rd level. Using accelerants (oils, alcohol, etc.) will deal max damage of its current level and increase the fire level by 1.
The fires turn is right after whatever/whoever's turn set the fire. This applies to fires started from other fires spreading.
Damage types and immunities to fire:
Objects can be of 3 varieties: wet / dry or / flammable. Wet objects are immune to the first level of fire. Hitting a wet object with a level 2 fire will only create a level 1 fire, then the object becomes dry. Dry take normal damage and flammable objects take double damage.
Putting out fires:
Players/creatures are able to put out fires in the squares next to them if they have something to put it out with (bucket of water, rug, clothing, shovel full of dirt).. Players/creatures are able to putout level 1 and level 4 fires without needed any assisting objects (ex. stomping it out). Level 2 fire is able to be smothered (ex. rugs, clothing, etc) the object used will be singed in the process or the fire can be reduced by 1 level by stomping, etc. A level 3 fire will need to be put out with water/ice/dirt or other inflammable objects/liquids. Each time a fire is attempted to be put out with an inflammable object reduce the level by 1. If a large amount of inflammable substance is used it may put out the fire completely or reduce it to level 1. Use your own digression for these instances.
Movement through fires:
Fires count as difficult terrain. Moving out of a fire you just set doesn't require a dexterity saving throw. Moving through a Level 1 and 4 fire require a dexterity save of 10 to not take damage. Level 2 is a dexterity save of 15. Level 3 is a dexterity save of 20. A fail of 10 or more may result in the player/creature falling into the fire. this is up to the dm
Please let me know what you think, as of typing this up I have not used in in our game. I will update more once it has been tested out in our campaign.
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