Conditional Event
A conditional event is used along with an inhibit gate, which is described in Inhibit Gate. In a fault tree with an inhibit gate, the output occurs only when the input events occur AND a conditional event is satisfied.
Example
From the fire triangle, we know that there will be fire when fuel and a heat source are present, given the presence of oxygen. The need for the presence of oxygen is the conditional event in the following tree. Inserting an inhibit gate also inserts the conditional event so that the condition that must be satisfied can be specified. The main purpose is to visually emphasize the presence of the condition, which is generally either a very rare or very common event.
