Controlled Immolation

 
Prerequisite(s): Exposure to fireball or delayed blast fireball spell.
 
Benefit: If you catch on fire, you take no damage from the flames. A creature striking you with its body or a handheld weapon takes 1d6 points of fire damage. The fire persists on your body for 1d4 rounds. This feat doesn't protect you from other sources of fire damage, whether magical or not, only from the effects of catching on fire. It also doesn't protect your equipment from the effects of fire.
 
Source: Unearthed Arcana