The good thing is that everyone around you has more critical failures in combat, the bad thing is - so do you!”— Fallout 2 In-game description
Fallout and Fallout 2Edit
All misses have 50% chance to be "upgraded" to a critical miss. This applies to every single entity in the game.
Presumably the same as in Fallout and Fallout 2, however the chance seems to be significantly lower.