Conflagration

Your Torso, neck, and eyes burn brightly before releasing a massive inferno around you.  This spell has no effect upon casting it,  but at the end of each of your turns, if you are still concentrating on this spell, you can release it.  The spell is released automatically if your concentration ends prematurely.  Releasing the spell causes a 25ft radius sphere around you to erupt into flames, forcing each creature within the sphere to make a Dexterity saving throw. A creature takes 5d10 fire damage on a failed save, and half as much on a successful one. Regardless of how many creatures are effected, you take fire damage equal to half the damage rolled upon releasing the spell.

For each turn that you concentrate on this spell without releasing it, the damage increases by 2d10.

The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried. 

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the base damage increases by 1d10 for each slot level above 5th.