The flames travel about one-fifth as far down a tunnel lined with ICF foams as they spread down a tunnel lined with wood. Practically any organic material, be it wood or plastic, gives off emissions when it is subjected to intense heat or flame. No matter what your walls are made of, there is no sense playing with fire. Building codes require covering the inside face of exterior walls with a fire-resistant material, such as gypsum wallboard or a stout plaster. In areas prone to outdoor fires, it is wise to finish the exterior with a fire-resistant material, too.
Favorites are Portland cement stucco and masonry.
And of course the more you can design your home to limit the exposure of flammable materials like wood and fabrics, the better. Evidence suggests that ICF walls may be safer in many ways than wood frame in a fire. Including ICF walls in your next home would provide an important and effective measure of fire safety.