Damp wood chips. The DR is +5 without them.
Short: 1 meter per rank of Power
Create billowing clouds of black smoke.
You cause a fire, either burning or recently extinguished, to give off excessive amounts of dark, billowing, smoke, obscuring visibility and making breathing difficult in an area up to P x P meters squared, where P is the caster's Power rating.
While at this density, the smoke produces a -15 penalty to spot checks as well as completely confounding the sense of smell.
If not contained in some other way, the smoke will stay in place for a number of rounds equal to the casters Power Modifier, then expand out to an area tariff that size for ssh n additional number of rounds equal to the Power Modifier. At this point, the spot check penalty is refused to -5 with a penalty of -15 for smell related perception checks.
Beyond that, the smoke dissipates at s natural rate.