Catching on Fire (3.5e Variant Rule)
From D&D Wiki
Characters exposed to burning oil, bonfires, and noninstantaneous magic fires such as a wall of fire might find their clothes, hair, or equipment on fire. Spells such as fireball or flame strike don't normally set a character on fire, since the heat and flame from these come and go in a flash.
Characters at risk of catching fire are allowed a DC 15 Reflex save to avoid this fate. If a character's clothes or hair catch fire, he takes 1d6 points of damage immediately. In each subsequent round, the burning character must make another Reflex saving throw. Failure means he takes another 1d6 points of damage that round. Success means that the fire has gone out. (That is, once he succeeds on his saving throw, he's no longer on fire.)
A character on fire may automatically extinguish the flames by jumping into enough water to douse himself. If no body of water is at hand, rolling on the ground or smothering the fire with cloaks or the like permits the character another save with a +4 bonus.
Those unlucky enough to have their clothes or equipment catch fire must make DC 15 Reflex saves for each item. Flammable items that fail take the same amount of damage as the character.