Rust-hued dust hangs in the air. The dust particles conduct and amplify certain types of energy and elemental forces.
Effect: The squares containing the cloud are lightly obscured. When a burst or a blast created by a fire, force, lightning, psychic, or thunder power touches a square of blast cloud, the size of the burst or blast is increased by 1.
Usage: A blast cloud encourages the characters (and their opponents) to remain farther apart than normal to avoid the enlarged areas of effect. Use this terrain in encounters featuring monsters that can take advantage of it, or when it can allow player characters who have attacks that might benefit from the blast cloud to take up an attractive combat position that utilizes the terrain’s effect.
Published in Dungeon Master's Guide 2, page(s) 58.