A little known fact is that if you are taking damage from an AOE*, like Rain of Fire, if you physically move out of the area being affected by the spell you stop taking damage almost immediately. As illustrated above our little raider turns his frown upside-down just by moving out of the rain of fire.
*AOE or Area of Effect: Many spells instead of targeting an individual target an area and do damage to everyone in that area regardless of how many people are in that area. So if 5 people are in the AOE 5 people will all take damage.
fire = bad