I was not exactly sure where to put this because it isnt only scenery or painting but here are my ideas for firey dammage.

Flaming Terrain- Transparent, thin orange/red/yellow cloth that is glued up. Since the cloth cant stand by itself, there could be a small fan under the "fire" that also makes the "fire" look like its moving around. For ashes, there could be some kind of black painted powder.

For blast marks- Take a model and put it on your terrain. Lightly spray directly over the model making a black blob with an unpainted area that in the middle of the blob that is shaped as the model. Then, take a brush and spread the paint outward from the center, making it look like whatever it was that made the mark exploded. Its kind of cartoony but it looked cool when I was priming my models on a piece of cardboard.

Dammaged models- Im not exaclty sure how to put flames on a model yet seeing that a fan could not fit on one but I have ideas for molten armor.

For molten shields- Create a crater or large mark on your models armour. Put a large amount of super glue around and inside the crater (this is to create a crumbly look on your model). After the glue is completely dried, paint some of the inside-sides of the crater red/orange and a metallic color with some brown mixed in. This makes the crater look like it is still hot or melted.

I was playing around with my paint and figured these out. I hope you find them useful.