The Phoenix Soul Sorcerer can ignite flammable objects like cloth with a touch. How should I handle this when a player playing such a character in one of my games ignites an enemies clothing? Specifically, what damage should being on fire deal and what should be necessary to end the effect? I'm looking for an answer that works well with existing material; it's not important that the answer be any sort of published rule.
As part of an answer, please indicate what you are balancing this use of the ability around and why in your adjustments to its function, so that I can understand where the suggestion is coming from when using that sort of approach to adjudicate the class ability.