There is a Legacy version here.


Source Player Core pg. 456
Effects with the fire trait deal fire damage or either conjure or manipulate fire. Those that manipulate fire have no effect in an area without fire. Creatures with this trait consist primarily of fire or have a connection to magical fire.

Planes with this trait are composed of flames that continually burn with no fuel source. Fire planes are extremely hostile to non-fire creatures. Unprotected wood, paper, cloth, and other flammable materials catch fire almost immediately, and creatures wearing unprotected flammable clothing catch fire, typically taking 1d6 persistent fire damage. Extraplanar creatures take moderate environmental fire damage at the end of each round (sometimes minor environmental damage in safer areas, or major or massive damage in even more fiery areas). Ice creatures are extremely uncomfortable on a fire plane, assuming they don’t outright melt in the heat.