OOC: At the very most it should be like disintegrate, in that it inflicts hit point damage, and you are turned into ash only if you are brought to below 0 hit points. Maybe Gansk can BoaA rule it as such for future pyroclastic dragons (please, please, I beg of you).
Round 705: The sloth tried to hide in corners, but Ash was able to use wingover to get close enough to breathe a cone of ash, accompanied by waves of sound. The sloth takes 16 points of fire and 16 points of sonic damage (rolled 17 Ref save). The sloth has 115 HP remaining, and is located at 0N110E. Ash is located at 20N100E20Z, flying southeast.