Falling -- The Animal/Natural Attack Types Table tells you which tables to use, the OB of a fall is the distance fallen.
Fire -- This one is more difficult, but essentially, Fire does a Heat critical each round that the person is on fire. The severity of the critical should likely correspond to how much on fire the person it.
As to how to set a person on fire, that will depend on the method used. Tossing them into a campfire (Hard Maneuver Roll), hitting them with a torch (i.e. club (-10 or -20) with fire crit one less severity), Using a spell, etc. One you know the method, then you can decide, as GM, how to handle the situation (OB vs. DB, Maneuver Roll, RR, etc..).